Differential roles of low and high spatial frequency content in abnormal facial emotion perception in schizophrenia.

PubMed

McBain, Ryan; Norton, Daniel; Chen, Yue

2010-09-01

While schizophrenia patients are impaired at facial emotion perception, the role of basic visual processing in this deficit remains relatively unclear. We examined emotion perception when spatial frequency content of facial images was manipulated via high-pass and low-pass filtering. Unlike controls (n=29), patients (n=30) perceived images with low spatial frequencies as more fearful than those without this information, across emotional salience levels. Patients also perceived images with high spatial frequencies as happier. In controls, this effect was found only at low emotional salience. These results indicate that basic visual processing has an amplified modulatory effect on emotion perception in schizophrenia. (c) 2010 Elsevier B.V. All rights reserved.

Spatial frequency filtered images reveal differences between masked and unmasked processing of emotional information.

PubMed

Rohr, Michaela; Wentura, Dirk

2014-10-01

High and low spatial frequency information has been shown to contribute differently to the processing of emotional information. In three priming studies using spatial frequency filtered emotional face primes, emotional face targets, and an emotion categorization task, we investigated this issue further. Differences in the pattern of results between short and masked, and short and long unmasked presentation conditions emerged. Given long and unmasked prime presentation, high and low frequency primes triggered emotion-specific priming effects. Given brief and masked prime presentation in Experiment 2, we found a dissociation: High frequency primes caused a valence priming effect, whereas low frequency primes yielded a differentiation between low and high arousing information within the negative domain. Brief and unmasked prime presentation in Experiment 3 revealed that subliminal processing of primes was responsible for the pattern observed in Experiment 2. The implications of these findings for theories of early emotional information processing are discussed. Copyright © 2014 Elsevier Inc. All rights reserved.

A new polishing process for large-aperture and high-precision aspheric surface

NASA Astrophysics Data System (ADS)

Nie, Xuqing; Li, Shengyi; Dai, Yifan; Song, Ci

2013-07-01

The high-precision aspheric surface is hard to be achieved due to the mid-spatial frequency error in the finishing step. The influence of mid-spatial frequency error is studied through the simulations and experiments. In this paper, a new polishing process based on magnetorheological finishing (MRF), smooth polishing (SP) and ion beam figuring (IBF) is proposed. A 400mm aperture parabolic surface is polished with this new process. The smooth polishing (SP) is applied after rough machining to control the MSF error. In the middle finishing step, most of low-spatial frequency error is removed by MRF rapidly, then the mid-spatial frequency error is restricted by SP, finally ion beam figuring is used to finish the surface. The surface accuracy is improved from the initial 37.691nm (rms, 95% aperture) to the final 4.195nm. The results show that the new polishing process is effective to manufacture large-aperture and high-precision aspheric surface.

Is attention based on spatial contextual memory preferentially guided by low spatial frequency signals?

PubMed

Patai, Eva Zita; Buckley, Alice; Nobre, Anna Christina

2013-01-01

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception.

Is Attention Based on Spatial Contextual Memory Preferentially Guided by Low Spatial Frequency Signals?

PubMed Central

Patai, Eva Zita; Buckley, Alice; Nobre, Anna Christina

2013-01-01

A popular model of visual perception states that coarse information (carried by low spatial frequencies) along the dorsal stream is rapidly transmitted to prefrontal and medial temporal areas, activating contextual information from memory, which can in turn constrain detailed input carried by high spatial frequencies arriving at a slower rate along the ventral visual stream, thus facilitating the processing of ambiguous visual stimuli. We were interested in testing whether this model contributes to memory-guided orienting of attention. In particular, we asked whether global, low-spatial frequency (LSF) inputs play a dominant role in triggering contextual memories in order to facilitate the processing of the upcoming target stimulus. We explored this question over four experiments. The first experiment replicated the LSF advantage reported in perceptual discrimination tasks by showing that participants were faster and more accurate at matching a low spatial frequency version of a scene, compared to a high spatial frequency version, to its original counterpart in a forced-choice task. The subsequent three experiments tested the relative contributions of low versus high spatial frequencies during memory-guided covert spatial attention orienting tasks. Replicating the effects of memory-guided attention, pre-exposure to scenes associated with specific spatial memories for target locations (memory cues) led to higher perceptual discrimination and faster response times to identify targets embedded in the scenes. However, either high or low spatial frequency cues were equally effective; LSF signals did not selectively or preferentially contribute to the memory-driven attention benefits to performance. Our results challenge a generalized model that LSFs activate contextual memories, which in turn bias attention and facilitate perception. PMID:23776509

Design Considerations of Polishing Lap for Computer-Controlled Cylindrical Polishing Process

NASA Technical Reports Server (NTRS)

Khan, Gufran S.; Gubarev, Mikhail; Arnold, William; Ramsey, Brian D.

2009-01-01

This paper establishes a relationship between the polishing process parameters and the generation of mid spatial-frequency error. The consideration of the polishing lap design to optimize the process in order to keep residual errors to a minimum and optimization of the process (speeds, stroke, etc.) and to keep the residual mid spatial-frequency error to a minimum, is also presented.

Face Recognition Is Affected by Similarity in Spatial Frequency Range to a Greater Degree Than Within-Category Object Recognition

ERIC Educational Resources Information Center

Collin, Charles A.; Liu, Chang Hong; Troje, Nikolaus F.; McMullen, Patricia A.; Chaudhuri, Avi

2004-01-01

Previous studies have suggested that face identification is more sensitive to variations in spatial frequency content than object recognition, but none have compared how sensitive the 2 processes are to variations in spatial frequency overlap (SFO). The authors tested face and object matching accuracy under varying SFO conditions. Their results…

A multistream model of visual word recognition.

PubMed

Allen, Philip A; Smith, Albert F; Lien, Mei-Ching; Kaut, Kevin P; Canfield, Angie

2009-02-01

Four experiments are reported that test a multistream model of visual word recognition, which associates letter-level and word-level processing channels with three known visual processing streams isolated in macaque monkeys: the magno-dominated (MD) stream, the interblob-dominated (ID) stream, and the blob-dominated (BD) stream (Van Essen & Anderson, 1995). We show that mixing the color of adjacent letters of words does not result in facilitation of response times or error rates when the spatial-frequency pattern of a whole word is familiar. However, facilitation does occur when the spatial-frequency pattern of a whole word is not familiar. This pattern of results is not due to different luminance levels across the different-colored stimuli and the background because isoluminant displays were used. Also, the mixed-case, mixed-hue facilitation occurred when different display distances were used (Experiments 2 and 3), so this suggests that image normalization can adjust independently of object size differences. Finally, we show that this effect persists in both spaced and unspaced conditions (Experiment 4)--suggesting that inappropriate letter grouping by hue cannot account for these results. These data support a model of visual word recognition in which lower spatial frequencies are processed first in the more rapid MD stream. The slower ID and BD streams may process some lower spatial frequency information in addition to processing higher spatial frequency information, but these channels tend to lose the processing race to recognition unless the letter string is unfamiliar to the MD stream--as with mixed-case presentation.

Cerebral Correlates of Emotional and Action Appraisals During Visual Processing of Emotional Scenes Depending on Spatial Frequency: A Pilot Study

PubMed Central

Campagne, Aurélie; Fradcourt, Benoit; Pichat, Cédric; Baciu, Monica; Kauffmann, Louise; Peyrin, Carole

2016-01-01

Visual processing of emotional stimuli critically depends on the type of cognitive appraisal involved. The present fMRI pilot study aimed to investigate the cerebral correlates involved in the visual processing of emotional scenes in two tasks, one emotional, based on the appraisal of personal emotional experience, and the other motivational, based on the appraisal of the tendency to action. Given that the use of spatial frequency information is relatively flexible during the visual processing of emotional stimuli depending on the task’s demands, we also explored the effect of the type of spatial frequency in visual stimuli in each task by using emotional scenes filtered in low spatial frequency (LSF) and high spatial frequencies (HSF). Activation was observed in the visual areas of the fusiform gyrus for all emotional scenes in both tasks, and in the amygdala for unpleasant scenes only. The motivational task induced additional activation in frontal motor-related areas (e.g. premotor cortex, SMA) and parietal regions (e.g. superior and inferior parietal lobules). Parietal regions were recruited particularly during the motivational appraisal of approach in response to pleasant scenes. These frontal and parietal activations, respectively, suggest that motor and navigation processes play a specific role in the identification of the tendency to action in the motivational task. Furthermore, activity observed in the motivational task, in response to both pleasant and unpleasant scenes, was significantly greater for HSF than for LSF scenes, suggesting that the tendency to action is driven mainly by the detailed information contained in scenes. Results for the emotional task suggest that spatial frequencies play only a small role in the evaluation of unpleasant and pleasant emotions. Our preliminary study revealed a partial distinction between visual processing of emotional scenes during identification of the tendency to action, and during identification of personal emotional experiences. It also illustrates flexible use of the spatial frequencies contained in scenes depending on their emotional valence and on task demands. PMID:26757433

Effects of spatial frequency and location of fearful faces on human amygdala activity.

PubMed

Morawetz, Carmen; Baudewig, Juergen; Treue, Stefan; Dechent, Peter

2011-01-31

Facial emotion perception plays a fundamental role in interpersonal social interactions. Images of faces contain visual information at various spatial frequencies. The amygdala has previously been reported to be preferentially responsive to low-spatial frequency (LSF) rather than to high-spatial frequency (HSF) filtered images of faces presented at the center of the visual field. Furthermore, it has been proposed that the amygdala might be especially sensitive to affective stimuli in the periphery. In the present study we investigated the impact of spatial frequency and stimulus eccentricity on face processing in the human amygdala and fusiform gyrus using functional magnetic resonance imaging (fMRI). The spatial frequencies of pictures of fearful faces were filtered to produce images that retained only LSF or HSF information. Facial images were presented either in the left or right visual field at two different eccentricities. In contrast to previous findings, we found that the amygdala responds to LSF and HSF stimuli in a similar manner regardless of the location of the affective stimuli in the visual field. Furthermore, the fusiform gyrus did not show differential responses to spatial frequency filtered images of faces. Our findings argue against the view that LSF information plays a crucial role in the processing of facial expressions in the amygdala and of a higher sensitivity to affective stimuli in the periphery. Copyright © 2010 Elsevier B.V. All rights reserved.

Spatial Frequency Priming of Scene Perception in Adolescents with and without ASD

ERIC Educational Resources Information Center

Vanmarcke, Steven; Noens, Ilse; Steyaert, Jean; Wagemans, Johan

2017-01-01

While most typically developing (TD) participants have a coarse-to-fine processing style, people with autism spectrum disorder (ASD) seem to be less globally and more locally biased when processing visual information. The stimulus-specific spatial frequency content might be directly relevant to determine this temporal hierarchy of visual…

High-dynamic-range scene compression in humans

NASA Astrophysics Data System (ADS)

McCann, John J.

2006-02-01

Single pixel dynamic-range compression alters a particular input value to a unique output value - a look-up table. It is used in chemical and most digital photographic systems having S-shaped transforms to render high-range scenes onto low-range media. Post-receptor neural processing is spatial, as shown by the physiological experiments of Dowling, Barlow, Kuffler, and Hubel & Wiesel. Human vision does not render a particular receptor-quanta catch as a unique response. Instead, because of spatial processing, the response to a particular quanta catch can be any color. Visual response is scene dependent. Stockham proposed an approach to model human range compression using low-spatial frequency filters. Campbell, Ginsberg, Wilson, Watson, Daly and many others have developed spatial-frequency channel models. This paper describes experiments measuring the properties of desirable spatial-frequency filters for a variety of scenes. Given the radiances of each pixel in the scene and the observed appearances of objects in the image, one can calculate the visual mask for that individual image. Here, visual mask is the spatial pattern of changes made by the visual system in processing the input image. It is the spatial signature of human vision. Low-dynamic range images with many white areas need no spatial filtering. High-dynamic-range images with many blacks, or deep shadows, require strong spatial filtering. Sun on the right and shade on the left requires directional filters. These experiments show that variable scene- scenedependent filters are necessary to mimic human vision. Although spatial-frequency filters can model human dependent appearances, the problem still remains that an analysis of the scene is still needed to calculate the scene-dependent strengths of each of the filters for each frequency.

Modulation of microsaccades by spatial frequency during object categorization.

PubMed

Craddock, Matt; Oppermann, Frank; Müller, Matthias M; Martinovic, Jasna

2017-01-01

The organization of visual processing into a coarse-to-fine information processing based on the spatial frequency properties of the input forms an important facet of the object recognition process. During visual object categorization tasks, microsaccades occur frequently. One potential functional role of these eye movements is to resolve high spatial frequency information. To assess this hypothesis, we examined the rate, amplitude and speed of microsaccades in an object categorization task in which participants viewed object and non-object images and classified them as showing either natural objects, man-made objects or non-objects. Images were presented unfiltered (broadband; BB) or filtered to contain only low (LSF) or high spatial frequency (HSF) information. This allowed us to examine whether microsaccades were modulated independently by the presence of a high-level feature - the presence of an object - and by low-level stimulus characteristics - spatial frequency. We found a bimodal distribution of saccades based on their amplitude, with a split between smaller and larger microsaccades at 0.4° of visual angle. The rate of larger saccades (⩾0.4°) was higher for objects than non-objects, and higher for objects with high spatial frequency content (HSF and BB objects) than for LSF objects. No effects were observed for smaller microsaccades (<0.4°). This is consistent with a role for larger microsaccades in resolving HSF information for object identification, and previous evidence that more microsaccades are directed towards informative image regions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of chronic and acute low-frequency repetitive transcranial magnetic stimulation on spatial memory in rats.

PubMed

Li, Wei; Yang, Yuye; Ye, Qing; Yang, Bo; Wang, Zhengrong

2007-03-15

Repetitive transcranial magnetic stimulation (rTMS) is a novel, non-invasive neurological and psychiatric tool. The low-frequency (1 Hz or less) rTMS is likely to play a particular role in its mechanism of action with different effects in comparison with high-frequency (>1 Hz) rTMS. There is limited information regarding the effect of low-frequency rTMS on spatial memory. In our study, each male Wistar rat was daily given 300 stimuli (1.0 T, 200 micros) at a rate of 0.5 Hz or sham stimulation. We investigated the effects of chronic and acute rTMS on reference/working memory process in Morris water maze test with the hypothesis that the effect would differ by chronic or acute condition. Chronic low-frequency rTMS impaired the retrieval of spatial short- and long-term spatial reference memory but not acquisition process and working memory, whereas acute low-frequency rTMS predominantly induced no deficits in acquisition or short-term spatial reference memory as well as working memory except for long-term reference memory. In summary, chronic 0.5 Hz rTMS disrupts spatial short- and long-term reference memory function, but acute rTMS differently affects reference memory. Chronic low-frequency rTMS may be used to modulate reference memory. Treatment protocols using low-frequency rTMS in neurological and psychiatric disorders need to take into account the potential effect of chronic low-frequency rTMS on memory and other cognitive functions.

Parallel processing of general and specific threat during early stages of perception

PubMed Central

2016-01-01

Differential processing of threat can consummate as early as 100 ms post-stimulus. Moreover, early perception not only differentiates threat from non-threat stimuli but also distinguishes among discrete threat subtypes (e.g. fear, disgust and anger). Combining spatial-frequency-filtered images of fear, disgust and neutral scenes with high-density event-related potentials and intracranial source estimation, we investigated the neural underpinnings of general and specific threat processing in early stages of perception. Conveyed in low spatial frequencies, fear and disgust images evoked convergent visual responses with similarly enhanced N1 potentials and dorsal visual (middle temporal gyrus) cortical activity (relative to neutral cues; peaking at 156 ms). Nevertheless, conveyed in high spatial frequencies, fear and disgust elicited divergent visual responses, with fear enhancing and disgust suppressing P1 potentials and ventral visual (occipital fusiform) cortical activity (peaking at 121 ms). Therefore, general and specific threat processing operates in parallel in early perception, with the ventral visual pathway engaged in specific processing of discrete threats and the dorsal visual pathway in general threat processing. Furthermore, selectively tuned to distinctive spatial-frequency channels and visual pathways, these parallel processes underpin dimensional and categorical threat characterization, promoting efficient threat response. These findings thus lend support to hybrid models of emotion. PMID:26412811

Beyond attentional bias: a perceptual bias in a dot-probe task.

PubMed

Bocanegra, Bruno R; Huijding, Jorg; Zeelenberg, René

2012-12-01

Previous dot-probe studies indicate that threat-related face cues induce a bias in spatial attention. Independently of spatial attention, a recent psychophysical study suggests that a bilateral fearful face cue improves low spatial-frequency perception (LSF) and impairs high spatial-frequency perception (HSF). Here, we combine these separate lines of research within a single dot-probe paradigm. We found that a bilateral fearful face cue, compared with a bilateral neutral face cue, speeded up responses to LSF targets and slowed down responses to HSF targets. This finding is important, as it shows that emotional cues in dot-probe tasks not only bias where information is preferentially processed (i.e., an attentional bias in spatial location), but also bias what type of information is preferentially processed (i.e., a perceptual bias in spatial frequency). PsycINFO Database Record (c) 2012 APA, all rights reserved.

Spatial-frequency dependent binocular imbalance in amblyopia

PubMed Central

Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C.; Bex, Peter J.

2015-01-01

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy. PMID:26603125

Spatial-frequency dependent binocular imbalance in amblyopia.

PubMed

Kwon, MiYoung; Wiecek, Emily; Dakin, Steven C; Bex, Peter J

2015-11-25

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy.

Emotion improves and impairs early vision.

PubMed

Bocanegra, Bruno R; Zeelenberg, René

2009-06-01

Recent studies indicate that emotion enhances early vision, but the generality of this finding remains unknown. Do the benefits of emotion extend to all basic aspects of vision, or are they limited in scope? Our results show that the brief presentation of a fearful face, compared with a neutral face, enhances sensitivity for the orientation of subsequently presented low-spatial-frequency stimuli, but diminishes orientation sensitivity for high-spatial-frequency stimuli. This is the first demonstration that emotion not only improves but also impairs low-level vision. The selective low-spatial-frequency benefits are consistent with the idea that emotion enhances magnocellular processing. Additionally, we suggest that the high-spatial-frequency deficits are due to inhibitory interactions between magnocellular and parvocellular pathways. Our results suggest an emotion-induced trade-off in visual processing, rather than a general improvement. This trade-off may benefit perceptual dimensions that are relevant for survival at the expense of those that are less relevant.

Selective spatial attention modulates bottom-up informational masking of speech

PubMed Central

Carlile, Simon; Corkhill, Caitlin

2015-01-01

To hear out a conversation against other talkers listeners overcome energetic and informational masking. Largely attributed to top-down processes, information masking has also been demonstrated using unintelligible speech and amplitude-modulated maskers suggesting bottom-up processes. We examined the role of speech-like amplitude modulations in information masking using a spatial masking release paradigm. Separating a target talker from two masker talkers produced a 20 dB improvement in speech reception threshold; 40% of which was attributed to a release from informational masking. When across frequency temporal modulations in the masker talkers are decorrelated the speech is unintelligible, although the within frequency modulation characteristics remains identical. Used as a masker as above, the information masking accounted for 37% of the spatial unmasking seen with this masker. This unintelligible and highly differentiable masker is unlikely to involve top-down processes. These data provides strong evidence of bottom-up masking involving speech-like, within-frequency modulations and that this, presumably low level process, can be modulated by selective spatial attention. PMID:25727100

Selective spatial attention modulates bottom-up informational masking of speech.

PubMed

Carlile, Simon; Corkhill, Caitlin

2015-03-02

To hear out a conversation against other talkers listeners overcome energetic and informational masking. Largely attributed to top-down processes, information masking has also been demonstrated using unintelligible speech and amplitude-modulated maskers suggesting bottom-up processes. We examined the role of speech-like amplitude modulations in information masking using a spatial masking release paradigm. Separating a target talker from two masker talkers produced a 20 dB improvement in speech reception threshold; 40% of which was attributed to a release from informational masking. When across frequency temporal modulations in the masker talkers are decorrelated the speech is unintelligible, although the within frequency modulation characteristics remains identical. Used as a masker as above, the information masking accounted for 37% of the spatial unmasking seen with this masker. This unintelligible and highly differentiable masker is unlikely to involve top-down processes. These data provides strong evidence of bottom-up masking involving speech-like, within-frequency modulations and that this, presumably low level process, can be modulated by selective spatial attention.

A Spatial Frequency Account of the Detriment that Local Processing of Navon Letters Has on Face Recognition

ERIC Educational Resources Information Center

Hills, Peter J.; Lewis, Michael B.

2009-01-01

Five minutes of processing the local features of a Navon letter causes a detriment in subsequent face-recognition performance (Macrae & Lewis, 2002). We hypothesize a perceptual after effect explanation of this effect in which face recognition is less accurate after adapting to high-spatial frequencies at high contrasts. Five experiments were…

The role of spatial frequency information for ERP components sensitive to faces and emotional facial expression.

PubMed

Holmes, Amanda; Winston, Joel S; Eimer, Martin

2005-10-01

To investigate the impact of spatial frequency on emotional facial expression analysis, ERPs were recorded in response to low spatial frequency (LSF), high spatial frequency (HSF), and unfiltered broad spatial frequency (BSF) faces with fearful or neutral expressions, houses, and chairs. In line with previous findings, BSF fearful facial expressions elicited a greater frontal positivity than BSF neutral facial expressions, starting at about 150 ms after stimulus onset. In contrast, this emotional expression effect was absent for HSF and LSF faces. Given that some brain regions involved in emotion processing, such as amygdala and connected structures, are selectively tuned to LSF visual inputs, these data suggest that ERP effects of emotional facial expression do not directly reflect activity in these regions. It is argued that higher order neocortical brain systems are involved in the generation of emotion-specific waveform modulations. The face-sensitive N170 component was neither affected by emotional facial expression nor by spatial frequency information.

Exploring the parahippocampal cortex response to high and low spatial frequency spaces.

PubMed

Zeidman, Peter; Mullally, Sinéad L; Schwarzkopf, Dietrich Samuel; Maguire, Eleanor A

2012-05-30

The posterior parahippocampal cortex (PHC) supports a range of cognitive functions, in particular scene processing. However, it has recently been suggested that PHC engagement during functional MRI simply reflects the representation of three-dimensional local space. If so, PHC should respond to space in the absence of scenes, geometric layout, objects or contextual associations. It has also been reported that PHC activation may be influenced by low-level visual properties of stimuli such as spatial frequency. Here, we tested whether PHC was responsive to the mere sense of space in highly simplified stimuli, and whether this was affected by their spatial frequency distribution. Participants were scanned using functional MRI while viewing depictions of simple three-dimensional space, and matched control stimuli that did not depict a space. Half the stimuli were low-pass filtered to ascertain the impact of spatial frequency. We observed a significant interaction between space and spatial frequency in bilateral PHC. Specifically, stimuli depicting space (more than nonspatial stimuli) engaged the right PHC when they featured high spatial frequencies. In contrast, the interaction in the left PHC did not show a preferential response to space. We conclude that a simple depiction of three-dimensional space that is devoid of objects, scene layouts or contextual associations is sufficient to robustly engage the right PHC, at least when high spatial frequencies are present. We suggest that coding for the presence of space may be a core function of PHC, and could explain its engagement in a range of tasks, including scene processing, where space is always present.

Age effects on visual-perceptual processing and confrontation naming.

PubMed

Gutherie, Audrey H; Seely, Peter W; Beacham, Lauren A; Schuchard, Ronald A; De l'Aune, William A; Moore, Anna Bacon

2010-03-01

The impact of age-related changes in visual-perceptual processing on naming ability has not been reported. The present study investigated the effects of 6 levels of spatial frequency and 6 levels of contrast on accuracy and latency to name objects in 14 young and 13 older neurologically normal adults with intact lexical-semantic functioning. Spatial frequency and contrast manipulations were made independently. Consistent with the hypotheses, variations in these two visual parameters impact naming ability in young and older subjects differently. The results from the spatial frequency-manipulations revealed that, in general, young vs. older subjects are faster and more accurate to name. However, this age-related difference is dependent on the spatial frequency on the image; differences were only seen for images presented at low (e.g., 0.25-1 c/deg) or high (e.g., 8-16 c/deg) spatial frequencies. Contrary to predictions, the results from the contrast manipulations revealed that overall older vs. young adults are more accurate to name. Again, however, differences were only seen for images presented at the lower levels of contrast (i.e., 1.25%). Both age groups had shorter latencies on the second exposure of the contrast-manipulated images, but this possible advantage of exposure was not seen for spatial frequency. Category analyses conducted on the data from this study indicate that older vs. young adults exhibit a stronger nonliving-object advantage for naming spatial frequency-manipulated images. Moreover, the findings suggest that bottom-up visual-perceptual variables integrate with top-down category information in different ways. Potential implications on the aging and naming (and recognition) literature are discussed.

Experimental power spectral density analysis for mid- to high-spatial frequency surface error control.

PubMed

Hoyo, Javier Del; Choi, Heejoo; Burge, James H; Kim, Geon-Hee; Kim, Dae Wook

2017-06-20

The control of surface errors as a function of spatial frequency is critical during the fabrication of modern optical systems. A large-scale surface figure error is controlled by a guided removal process, such as computer-controlled optical surfacing. Smaller-scale surface errors are controlled by polishing process parameters. Surface errors of only a few millimeters may degrade the performance of an optical system, causing background noise from scattered light and reducing imaging contrast for large optical systems. Conventionally, the microsurface roughness is often given by the root mean square at a high spatial frequency range, with errors within a 0.5×0.5  mm local surface map with 500×500 pixels. This surface specification is not adequate to fully describe the characteristics for advanced optical systems. The process for controlling and minimizing mid- to high-spatial frequency surface errors with periods of up to ∼2-3  mm was investigated for many optical fabrication conditions using the measured surface power spectral density (PSD) of a finished Zerodur optical surface. Then, the surface PSD was systematically related to various fabrication process parameters, such as the grinding methods, polishing interface materials, and polishing compounds. The retraceable experimental polishing conditions and processes used to produce an optimal optical surface PSD are presented.

Basic abnormalities in visual processing affect face processing at an early age in autism spectrum disorder.

PubMed

Vlamings, Petra Hendrika Johanna Maria; Jonkman, Lisa Marthe; van Daalen, Emma; van der Gaag, Rutger Jan; Kemner, Chantal

2010-12-15

A detailed visual processing style has been noted in autism spectrum disorder (ASD); this contributes to problems in face processing and has been directly related to abnormal processing of spatial frequencies (SFs). Little is known about the early development of face processing in ASD and the relation with abnormal SF processing. We investigated whether young ASD children show abnormalities in low spatial frequency (LSF, global) and high spatial frequency (HSF, detailed) processing and explored whether these are crucially involved in the early development of face processing. Three- to 4-year-old children with ASD (n = 22) were compared with developmentally delayed children without ASD (n = 17). Spatial frequency processing was studied by recording visual evoked potentials from visual brain areas while children passively viewed gratings (HSF/LSF). In addition, children watched face stimuli with different expressions, filtered to include only HSF or LSF. Enhanced activity in visual brain areas was found in response to HSF versus LSF information in children with ASD, in contrast to control subjects. Furthermore, facial-expression processing was also primarily driven by detail in ASD. Enhanced visual processing of detailed (HSF) information is present early in ASD and occurs for neutral (gratings), as well as for socially relevant stimuli (facial expressions). These data indicate that there is a general abnormality in visual SF processing in early ASD and are in agreement with suggestions that a fast LSF subcortical face processing route might be affected in ASD. This could suggest that abnormal visual processing is causative in the development of social problems in ASD. Copyright © 2010 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Abnormalities of Object Visual Processing in Body Dysmorphic Disorder

PubMed Central

Feusner, Jamie D.; Hembacher, Emily; Moller, Hayley; Moody, Teena D.

2013-01-01

Background Individuals with body dysmorphic disorder may have perceptual distortions for their appearance. Previous studies suggest imbalances in detailed relative to configural/holistic visual processing when viewing faces. No study has investigated the neural correlates of processing non-symptom-related stimuli. The objective of this study was to determine whether individuals with body dysmorphic disorder have abnormal patterns of brain activation when viewing non-face/non-body object stimuli. Methods Fourteen medication-free participants with DSM-IV body dysmorphic disorder and 14 healthy controls participated. We performed functional magnetic resonance imaging while participants matched photographs of houses that were unaltered, contained only high spatial frequency (high detail) information, or only low spatial frequency (low detail) information. The primary outcome was group differences in blood oxygen level-dependent signal changes. Results The body dysmorphic disorder group showed lesser activity in the parahippocampal gyrus, lingual gyrus, and precuneus for low spatial frequency images. There were greater activations in medial prefrontal regions for high spatial frequency images, although no significant differences when compared to a low-level baseline. Greater symptom severity was associated with lesser activity in dorsal occipital cortex and ventrolateral prefrontal cortex for normal and high spatial frequency images. Conclusions Individuals with body dysmorphic disorder have abnormal brain activation patterns when viewing objects. Hypoactivity in visual association areas for configural and holistic (low detail) elements and abnormal allocation of prefrontal systems for details is consistent with a model of imbalances in global vs. local processing. This may occur not only for appearance but also for general stimuli unrelated to their symptoms. PMID:21557897

Spatial frequency supports the emergence of categorical representations in visual cortex during natural scene perception.

PubMed

Dima, Diana C; Perry, Gavin; Singh, Krish D

2018-06-11

In navigating our environment, we rapidly process and extract meaning from visual cues. However, the relationship between visual features and categorical representations in natural scene perception is still not well understood. Here, we used natural scene stimuli from different categories and filtered at different spatial frequencies to address this question in a passive viewing paradigm. Using representational similarity analysis (RSA) and cross-decoding of magnetoencephalography (MEG) data, we show that categorical representations emerge in human visual cortex at ∼180 ms and are linked to spatial frequency processing. Furthermore, dorsal and ventral stream areas reveal temporally and spatially overlapping representations of low and high-level layer activations extracted from a feedforward neural network. Our results suggest that neural patterns from extrastriate visual cortex switch from low-level to categorical representations within 200 ms, highlighting the rapid cascade of processing stages essential in human visual perception. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

FIND: difFerential chromatin INteractions Detection using a spatial Poisson process

PubMed Central

Chen, Yang; Zhang, Michael Q.

2018-01-01

Polymer-based simulations and experimental studies indicate the existence of a spatial dependency between the adjacent DNA fibers involved in the formation of chromatin loops. However, the existing strategies for detecting differential chromatin interactions assume that the interacting segments are spatially independent from the other segments nearby. To resolve this issue, we developed a new computational method, FIND, which considers the local spatial dependency between interacting loci. FIND uses a spatial Poisson process to detect differential chromatin interactions that show a significant difference in their interaction frequency and the interaction frequency of their neighbors. Simulation and biological data analysis show that FIND outperforms the widely used count-based methods and has a better signal-to-noise ratio. PMID:29440282

Recognition memory for low- and high-frequency-filtered emotional faces: Low spatial frequencies drive emotional memory enhancement, whereas high spatial frequencies drive the emotion-induced recognition bias.

PubMed

Rohr, Michaela; Tröger, Johannes; Michely, Nils; Uhde, Alarith; Wentura, Dirk

2017-07-01

This article deals with two well-documented phenomena regarding emotional stimuli: emotional memory enhancement-that is, better long-term memory for emotional than for neutral stimuli-and the emotion-induced recognition bias-that is, a more liberal response criterion for emotional than for neutral stimuli. Studies on visual emotion perception and attention suggest that emotion-related processes can be modulated by means of spatial-frequency filtering of the presented emotional stimuli. Specifically, low spatial frequencies are assumed to play a primary role for the influence of emotion on attention and judgment. Given this theoretical background, we investigated whether spatial-frequency filtering also impacts (1) the memory advantage for emotional faces and (2) the emotion-induced recognition bias, in a series of old/new recognition experiments. Participants completed incidental-learning tasks with high- (HSF) and low- (LSF) spatial-frequency-filtered emotional and neutral faces. The results of the surprise recognition tests showed a clear memory advantage for emotional stimuli. Most importantly, the emotional memory enhancement was significantly larger for face images containing only low-frequency information (LSF faces) than for HSF faces across all experiments, suggesting that LSF information plays a critical role in this effect, whereas the emotion-induced recognition bias was found only for HSF stimuli. We discuss our findings in terms of both the traditional account of different processing pathways for HSF and LSF information and a stimulus features account. The double dissociation in the results favors the latter account-that is, an explanation in terms of differences in the characteristics of HSF and LSF stimuli.

Frequency conversion of structured light.

PubMed

Steinlechner, Fabian; Hermosa, Nathaniel; Pruneri, Valerio; Torres, Juan P

2016-02-15

Coherent frequency conversion of structured light, i.e. the ability to manipulate the carrier frequency of a wave front without distorting its spatial phase and intensity profile, provides the opportunity for numerous novel applications in photonic technology and fundamental science. In particular, frequency conversion of spatial modes carrying orbital angular momentum can be exploited in sub-wavelength resolution nano-optics and coherent imaging at a wavelength different from that used to illuminate an object. Moreover, coherent frequency conversion will be crucial for interfacing information stored in the high-dimensional spatial structure of single and entangled photons with various constituents of quantum networks. In this work, we demonstrate frequency conversion of structured light from the near infrared (803 nm) to the visible (527 nm). The conversion scheme is based on sum-frequency generation in a periodically poled lithium niobate crystal pumped with a 1540-nm Gaussian beam. We observe frequency-converted fields that exhibit a high degree of similarity with the input field and verify the coherence of the frequency-conversion process via mode projection measurements with a phase mask and a single-mode fiber. Our results demonstrate the suitability of exploiting the technique for applications in quantum information processing and coherent imaging.

The highs and lows of object impossibility: effects of spatial frequency on holistic processing of impossible objects.

PubMed

Freud, Erez; Avidan, Galia; Ganel, Tzvi

2015-02-01

Holistic processing, the decoding of a stimulus as a unified whole, is a basic characteristic of object perception. Recent research using Garner's speeded classification task has shown that this processing style is utilized even for impossible objects that contain an inherent spatial ambiguity. In particular, similar Garner interference effects were found for possible and impossible objects, indicating similar holistic processing styles for the two object categories. In the present study, we further investigated the perceptual mechanisms that mediate such holistic representation of impossible objects. We relied on the notion that, whereas information embedded in the high-spatial-frequency (HSF) content supports fine-detailed processing of object features, the information conveyed by low spatial frequencies (LSF) is more crucial for the emergence of a holistic shape representation. To test the effects of image frequency on the holistic processing of impossible objects, participants performed the Garner speeded classification task on images of possible and impossible cubes filtered for their LSF and HSF information. For images containing only LSF, similar interference effects were observed for possible and impossible objects, indicating that the two object categories were processed in a holistic manner. In contrast, for the HSF images, Garner interference was obtained only for possible, but not for impossible objects. Importantly, we provided evidence to show that this effect could not be attributed to a lack of sensitivity to object possibility in the LSF images. Particularly, even for full-spectrum images, Garner interference was still observed for both possible and impossible objects. Additionally, performance in an object classification task revealed high sensitivity to object possibility, even for LSF images. Taken together, these findings suggest that the visual system can tolerate the spatial ambiguity typical to impossible objects by relying on information embedded in LSF, whereas HSF information may underlie the visual system's susceptibility to distortions in objects' spatial layouts.

Effect of Temporal Constraints on Hemispheric Asymmetries during Spatial Frequency Processing

ERIC Educational Resources Information Center

Peyrin, Carole; Mermillod, Martial; Chokron, Sylvie; Marendaz, Christian

2006-01-01

Studies on functional hemispheric asymmetries have suggested that the right vs. left hemisphere should be predominantly involved in low vs. high spatial frequency (SF) analysis, respectively. By manipulating exposure duration of filtered natural scene images, we examined whether the temporal characteristics of SF analysis (i.e., the temporal…

High spatial resolution distributed optical fiber dynamic strain sensor with enhanced frequency and strain resolution.

PubMed

Masoudi, Ali; Newson, Trevor P

2017-01-15

A distributed optical fiber dynamic strain sensor with high spatial and frequency resolution is demonstrated. The sensor, which uses the ϕ-OTDR interrogation technique, exhibited a higher sensitivity thanks to an improved optical arrangement and a new signal processing procedure. The proposed sensing system is capable of fully quantifying multiple dynamic perturbations along a 5 km long sensing fiber with a frequency and spatial resolution of 5 Hz and 50 cm, respectively. The strain resolution of the sensor was measured to be 40 nε.

EEG source reconstruction reveals frontal-parietal dynamics of spatial conflict processing.

PubMed

Cohen, Michael X; Ridderinkhof, K Richard

2013-01-01

Cognitive control requires the suppression of distracting information in order to focus on task-relevant information. We applied EEG source reconstruction via time-frequency linear constrained minimum variance beamforming to help elucidate the neural mechanisms involved in spatial conflict processing. Human subjects performed a Simon task, in which conflict was induced by incongruence between spatial location and response hand. We found an early (∼200 ms post-stimulus) conflict modulation in stimulus-contralateral parietal gamma (30-50 Hz), followed by a later alpha-band (8-12 Hz) conflict modulation, suggesting an early detection of spatial conflict and inhibition of spatial location processing. Inter-regional connectivity analyses assessed via cross-frequency coupling of theta (4-8 Hz), alpha, and gamma power revealed conflict-induced shifts in cortical network interactions: Congruent trials (relative to incongruent trials) had stronger coupling between frontal theta and stimulus-contrahemifield parietal alpha/gamma power, whereas incongruent trials had increased theta coupling between medial frontal and lateral frontal regions. These findings shed new light into the large-scale network dynamics of spatial conflict processing, and how those networks are shaped by oscillatory interactions.

FIND: difFerential chromatin INteractions Detection using a spatial Poisson process.

PubMed

Djekidel, Mohamed Nadhir; Chen, Yang; Zhang, Michael Q

2018-02-12

Polymer-based simulations and experimental studies indicate the existence of a spatial dependency between the adjacent DNA fibers involved in the formation of chromatin loops. However, the existing strategies for detecting differential chromatin interactions assume that the interacting segments are spatially independent from the other segments nearby. To resolve this issue, we developed a new computational method, FIND, which considers the local spatial dependency between interacting loci. FIND uses a spatial Poisson process to detect differential chromatin interactions that show a significant difference in their interaction frequency and the interaction frequency of their neighbors. Simulation and biological data analysis show that FIND outperforms the widely used count-based methods and has a better signal-to-noise ratio. © 2018 Djekidel et al.; Published by Cold Spring Harbor Laboratory Press.

The spatial unmasking of speech: evidence for within-channel processing of interaural time delay.

PubMed

Edmonds, Barrie A; Culling, John F

2005-05-01

Across-frequency processing by common interaural time delay (ITD) in spatial unmasking was investigated by measuring speech reception thresholds (SRTs) for high- and low-frequency bands of target speech presented against concurrent speech or a noise masker. Experiment 1 indicated that presenting one of these target bands with an ITD of +500 micros and the other with zero ITD (like the masker) provided some release from masking, but full binaural advantage was only measured when both target bands were given an ITD of + 500 micros. Experiment 2 showed that full binaural advantage could also be achieved when the high- and low-frequency bands were presented with ITDs of equal but opposite magnitude (+/- 500 micros). In experiment 3, the masker was also split into high- and low-frequency bands with ITDs of equal but opposite magnitude (+/-500 micros). The ITD of the low-frequency target band matched that of the high-frequency masking band and vice versa. SRTs indicated that, as long as the target and masker differed in ITD within each frequency band, full binaural advantage could be achieved. These results suggest that the mechanism underlying spatial unmasking exploits differences in ITD independently within each frequency channel.

Audio-visual synchrony and spatial attention enhance processing of dynamic visual stimulation independently and in parallel: A frequency-tagging study.

PubMed

Covic, Amra; Keitel, Christian; Porcu, Emanuele; Schröger, Erich; Müller, Matthias M

2017-11-01

The neural processing of a visual stimulus can be facilitated by attending to its position or by a co-occurring auditory tone. Using frequency-tagging, we investigated whether facilitation by spatial attention and audio-visual synchrony rely on similar neural processes. Participants attended to one of two flickering Gabor patches (14.17 and 17 Hz) located in opposite lower visual fields. Gabor patches further "pulsed" (i.e. showed smooth spatial frequency variations) at distinct rates (3.14 and 3.63 Hz). Frequency-modulating an auditory stimulus at the pulse-rate of one of the visual stimuli established audio-visual synchrony. Flicker and pulsed stimulation elicited stimulus-locked rhythmic electrophysiological brain responses that allowed tracking the neural processing of simultaneously presented Gabor patches. These steady-state responses (SSRs) were quantified in the spectral domain to examine visual stimulus processing under conditions of synchronous vs. asynchronous tone presentation and when respective stimulus positions were attended vs. unattended. Strikingly, unique patterns of effects on pulse- and flicker driven SSRs indicated that spatial attention and audiovisual synchrony facilitated early visual processing in parallel and via different cortical processes. We found attention effects to resemble the classical top-down gain effect facilitating both, flicker and pulse-driven SSRs. Audio-visual synchrony, in turn, only amplified synchrony-producing stimulus aspects (i.e. pulse-driven SSRs) possibly highlighting the role of temporally co-occurring sights and sounds in bottom-up multisensory integration. Copyright © 2017 Elsevier Inc. All rights reserved.

A task-irrelevant stimulus attribute affects perception and short-term memory

PubMed Central

Huang, Jie; Kahana, Michael J.; Sekuler, Robert

2010-01-01

Selective attention protects cognition against intrusions of task-irrelevant stimulus attributes. This protective function was tested in coordinated psychophysical and memory experiments. Stimuli were superimposed, horizontally and vertically oriented gratings of varying spatial frequency; only one orientation was task relevant. Experiment 1 demonstrated that a task-irrelevant spatial frequency interfered with visual discrimination of the task-relevant spatial frequency. Experiment 2 adopted a two-item Sternberg task, using stimuli that had been scaled to neutralize interference at the level of vision. Despite being visually neutralized, the task-irrelevant attribute strongly influenced recognition accuracy and associated reaction times (RTs). This effect was sharply tuned, with the task-irrelevant spatial frequency having an impact only when the task-relevant spatial frequencies of the probe and study items were highly similar to one another. Model-based analyses of judgment accuracy and RT distributional properties converged on the point that the irrelevant orientation operates at an early stage in memory processing, not at a later one that supports decision making. PMID:19933454

Object Categorization in Finer Levels Relies More on Higher Spatial Frequencies and Takes Longer.

PubMed

Ashtiani, Matin N; Kheradpisheh, Saeed R; Masquelier, Timothée; Ganjtabesh, Mohammad

2017-01-01

The human visual system contains a hierarchical sequence of modules that take part in visual perception at different levels of abstraction, i.e., superordinate, basic, and subordinate levels. One important question is to identify the "entry" level at which the visual representation is commenced in the process of object recognition. For a long time, it was believed that the basic level had a temporal advantage over two others. This claim has been challenged recently. Here we used a series of psychophysics experiments, based on a rapid presentation paradigm, as well as two computational models, with bandpass filtered images of five object classes to study the processing order of the categorization levels. In these experiments, we investigated the type of visual information required for categorizing objects in each level by varying the spatial frequency bands of the input image. The results of our psychophysics experiments and computational models are consistent. They indicate that the different spatial frequency information had different effects on object categorization in each level. In the absence of high frequency information, subordinate and basic level categorization are performed less accurately, while the superordinate level is performed well. This means that low frequency information is sufficient for superordinate level, but not for the basic and subordinate levels. These finer levels rely more on high frequency information, which appears to take longer to be processed, leading to longer reaction times. Finally, to avoid the ceiling effect, we evaluated the robustness of the results by adding different amounts of noise to the input images and repeating the experiments. As expected, the categorization accuracy decreased and the reaction time increased significantly, but the trends were the same. This shows that our results are not due to a ceiling effect. The compatibility between our psychophysical and computational results suggests that the temporal advantage of the superordinate (resp. basic) level to basic (resp. subordinate) level is mainly due to the computational constraints (the visual system processes higher spatial frequencies more slowly, and categorization in finer levels depends more on these higher spatial frequencies).

Object Categorization in Finer Levels Relies More on Higher Spatial Frequencies and Takes Longer

PubMed Central

Ashtiani, Matin N.; Kheradpisheh, Saeed R.; Masquelier, Timothée; Ganjtabesh, Mohammad

2017-01-01

The human visual system contains a hierarchical sequence of modules that take part in visual perception at different levels of abstraction, i.e., superordinate, basic, and subordinate levels. One important question is to identify the “entry” level at which the visual representation is commenced in the process of object recognition. For a long time, it was believed that the basic level had a temporal advantage over two others. This claim has been challenged recently. Here we used a series of psychophysics experiments, based on a rapid presentation paradigm, as well as two computational models, with bandpass filtered images of five object classes to study the processing order of the categorization levels. In these experiments, we investigated the type of visual information required for categorizing objects in each level by varying the spatial frequency bands of the input image. The results of our psychophysics experiments and computational models are consistent. They indicate that the different spatial frequency information had different effects on object categorization in each level. In the absence of high frequency information, subordinate and basic level categorization are performed less accurately, while the superordinate level is performed well. This means that low frequency information is sufficient for superordinate level, but not for the basic and subordinate levels. These finer levels rely more on high frequency information, which appears to take longer to be processed, leading to longer reaction times. Finally, to avoid the ceiling effect, we evaluated the robustness of the results by adding different amounts of noise to the input images and repeating the experiments. As expected, the categorization accuracy decreased and the reaction time increased significantly, but the trends were the same. This shows that our results are not due to a ceiling effect. The compatibility between our psychophysical and computational results suggests that the temporal advantage of the superordinate (resp. basic) level to basic (resp. subordinate) level is mainly due to the computational constraints (the visual system processes higher spatial frequencies more slowly, and categorization in finer levels depends more on these higher spatial frequencies). PMID:28790954

Effect of scanning velocity on femtosecond laser-induced periodic surface structures on HgCdTe crystal

NASA Astrophysics Data System (ADS)

Gu, Hongan; Dai, Ye; Wang, Haodong; Yan, Xiaona; Ma, Guohong

2017-12-01

In this paper, a femtosecond laser line-scanning irradiation was used to induce the periodic surface microstructure on HgCdTe crystal. Low spatial frequency laser induced periodic surface structures of 650-770 nm and high spatial frequency laser induced periodic surface structures of 152-246 nm were respectively found with different scanning speeds. The evolution process from low spatial frequency laser induced periodic surface structures to high spatial frequency laser induced periodic surface structures is characterized by scanning electron microscope. Their spatial periods deduced by using a two-dimensional Fourier transformation partly agree with the predictions of the Sipe-Drude theory. Confocal micro-Raman spectral show that the atomic arrangement of induced low spatial frequency laser-induced structures are basically consistent with the crystal in the central area of laser-scanning line, however a new peak at 164 cm-1 for the CdTe-like mode becomes evident due to the Hg vaporization when strong laser ablation happens. The obtained surface periodic ripples may have applications in fabricating advanced infrared detector.

Comparison of the results of refractometric measurements in the process of diffusion, obtained by means of the backgroundoriented schlieren method and the holographic interferometry method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraiskii, A V; Mironova, T V

2015-08-31

The results of the study of interdiffusion of two liquids, obtained using the holographic recording scheme with a nonstationary reference wave with the frequency linearly varying in space and time are compared with the results of correlation processing of digital photographs, made with a random background screen. The spatio-temporal behaviour of the signal in four basic representations ('space – temporal frequency', 'space – time', 'spatial frequency – temporal frequency' and 'spatial frequency – time') is found in the holographic experiment and calculated (in the appropriate coordinates) based on the background-oriented schlieren method. Practical coincidence of the results of the correlationmore » analysis and the holographic double-exposure interferometry is demonstrated. (interferometry)« less

Real-time optical image processing techniques

NASA Technical Reports Server (NTRS)

Liu, Hua-Kuang

1988-01-01

Nonlinear real-time optical processing on spatial pulse frequency modulation has been pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the modification of micro-channel spatial light modulators (MSLMs). Micro-channel spatial light modulators are modified via the Fabry-Perot method to achieve the high gamma operation required for non-linear operation. Real-time nonlinear processing was performed using the halftone screen and MSLM. The experiments showed the effectiveness of the thresholding and also showed the needs of higher SBP for image processing. The Hughes LCLV has been characterized and found to yield high gamma (about 1.7) when operated in low frequency and low bias mode. Cascading of two LCLVs should also provide enough gamma for nonlinear processing. In this case, the SBP of the LCLV is sufficient but the uniformity of the LCLV needs improvement. These include image correlation, computer generation of holograms, pseudo-color image encoding for image enhancement, and associative-retrieval in neural processing. The discovery of the only known optical method for dynamic range compression of an input image in real-time by using GaAs photorefractive crystals is reported. Finally, a new architecture for non-linear multiple sensory, neural processing has been suggested.

Spatial frequency characteristics at image decision-point locations for observers with different radiological backgrounds in lung nodule detection

NASA Astrophysics Data System (ADS)

Pietrzyk, Mariusz W.; Manning, David J.; Dix, Alan; Donovan, Tim

2009-02-01

Aim: The goal of the study is to determine the spatial frequency characteristics at locations in the image of overt and covert observers' decisions and find out if there are any similarities in different observers' groups: the same radiological experience group or the same accuracy scored level. Background: The radiological task is described as a visual searching decision making procedure involving visual perception and cognitive processing. Humans perceive the world through a number of spatial frequency channels, each sensitive to visual information carried by different spatial frequency ranges and orientations. Recent studies have shown that particular physical properties of local and global image-based elements are correlated with the performance and the level of experience of human observers in breast cancer and lung nodule detections. Neurological findings in visual perception were an inspiration for wavelet applications in vision research because the methodology tries to mimic the brain processing algorithms. Methods: The wavelet approach to the set of postero-anterior chest radiographs analysis has been used to characterize perceptual preferences observers with different levels of experience in the radiological task. Psychophysical methodology has been applied to track eye movements over the image, where particular ROIs related to the observers' fixation clusters has been analysed in the spaces frame by Daubechies functions. Results: Significance differences have been found between the spatial frequency characteristics at the location of different decisions.

Priming Facial Gender and Emotional Valence: The Influence of Spatial Frequency on Face Perception in ASD

ERIC Educational Resources Information Center

Vanmarcke, Steven; Wagemans, Johan

2017-01-01

Adolescents with and without autism spectrum disorder (ASD) performed two priming experiments in which they implicitly processed a prime stimulus, containing high and/or low spatial frequency information, and then explicitly categorized a target face either as male/female (gender task) or as positive/negative (Valence task). Adolescents with ASD…

Newborns' Face Recognition Is Based on Spatial Frequencies below 0.5 Cycles per Degree

ERIC Educational Resources Information Center

de Heering, Adelaide; Turati, Chiara; Rossion, Bruno; Bulf, Hermann; Goffaux, Valerie; Simion, Francesca

2008-01-01

A critical question in Cognitive Science concerns how knowledge of specific domains emerges during development. Here we examined how limitations of the visual system during the first days of life may shape subsequent development of face processing abilities. By manipulating the bands of spatial frequencies of face images, we investigated what is…

EEG Source Reconstruction Reveals Frontal-Parietal Dynamics of Spatial Conflict Processing

PubMed Central

Cohen, Michael X; Ridderinkhof, K. Richard

2013-01-01

Cognitive control requires the suppression of distracting information in order to focus on task-relevant information. We applied EEG source reconstruction via time-frequency linear constrained minimum variance beamforming to help elucidate the neural mechanisms involved in spatial conflict processing. Human subjects performed a Simon task, in which conflict was induced by incongruence between spatial location and response hand. We found an early (∼200 ms post-stimulus) conflict modulation in stimulus-contralateral parietal gamma (30–50 Hz), followed by a later alpha-band (8–12 Hz) conflict modulation, suggesting an early detection of spatial conflict and inhibition of spatial location processing. Inter-regional connectivity analyses assessed via cross-frequency coupling of theta (4–8 Hz), alpha, and gamma power revealed conflict-induced shifts in cortical network interactions: Congruent trials (relative to incongruent trials) had stronger coupling between frontal theta and stimulus-contrahemifield parietal alpha/gamma power, whereas incongruent trials had increased theta coupling between medial frontal and lateral frontal regions. These findings shed new light into the large-scale network dynamics of spatial conflict processing, and how those networks are shaped by oscillatory interactions. PMID:23451201

Definition of SMOS Level 3 Land Products for the Villafranca del Castillo Data Processing Centre (CP34)

NASA Astrophysics Data System (ADS)

Lopez-Baeza, E.; Monsoriu Torres, A.; Font, J.; Alonso, O.

2009-04-01

The ESA SMOS (Soil Moisture and Ocean Salinity) Mission is planned to be launched in July 2009. The satellite will measure soil moisture over the continents and surface salinity of the oceans at resolutions that are sufficient for climatological-type studies. This paper describes the procedure to be used at the Spanish SMOS Level 3 and 4 Data Processing Centre (CP34) to generate Soil Moisture and other Land Surface Product maps from SMOS Level 2 data. This procedure can be used to map Soil Moisture, Vegetation Water Content and Soil Dielectric Constant data into different pre-defined spatial grids with fixed temporal frequency. The L3 standard Land Surface Products to be generated at CP34 are: Soil Moisture products: maximum spatial resolution with no spatial averaging, temporal averaging of 3 days, daily generation maximum spatial resolution with no spatial averaging, temporal averaging of 10 days, generation frequency of once every 10 days. b': maximum spatial resolution with no spatial averaging, temporal averaging of monthly decades (1st to 10th of the month, 11th to 20th of the month, 21st to last day of the month), generation frequency of once every decade monthly average, temporal averaging from L3 decade averages, monthly generation Seasonal average, temporal averaging from L3 monthly averages, seasonally generation yearly average, temporal averaging from L3 monthly averages, yearly generation Vegetation Water Content products: maximum spatial resolution with no spatial averaging, temporal averaging of 10 days, generation frequency of once every 10 days. a': maximum spatial resolution with no spatial averaging, temporal averaging of monthly decades (1st to 10th of the month, 11th to 20th of the month, 21st to last day of the month) using simple averaging method over the L2 products in ISEA grid, generation frequency of once every decade monthly average, temporal averaging from L3 decade averages, monthly generation seasonal average, temporal averaging from L3 monthly averages, seasonally generation yearly average, temporal averaging from L3 monthly averages, yearly generation Dielectric Constant products: (the dielectric constant products are delivered together with soil moisture products, with the same averaging periods and generation frequency): maximum spatial resolution with no spatial averaging, temporal averaging of 3 days, daily generation maximum spatial resolution with no spatial averaging, temporal averaging of 10 days, generation frequency of once every 10 days. b': maximum spatial resolution with no spatial averaging, temporal averaging of monthly decades (1st to 10th of the month, 11th to 20th of the month, 21st to last day of the month), generation frequency of once every decade monthly average, temporal averaging from L3 decade averages, monthly generation seasonal average, temporal averaging from L3 monthly averages, seasonally generation yearly average, temporal averaging from L3 monthly averages, yearly generation.

Multi-scale Slip Inversion Based on Simultaneous Spatial and Temporal Domain Wavelet Transform

NASA Astrophysics Data System (ADS)

Liu, W.; Yao, H.; Yang, H. Y.

2017-12-01

Finite fault inversion is a widely used method to study earthquake rupture processes. Some previous studies have proposed different methods to implement finite fault inversion, including time-domain, frequency-domain, and wavelet-domain methods. Many previous studies have found that different frequency bands show different characteristics of the seismic rupture (e.g., Wang and Mori, 2011; Yao et al., 2011, 2013; Uchide et al., 2013; Yin et al., 2017). Generally, lower frequency waveforms correspond to larger-scale rupture characteristics while higher frequency data are representative of smaller-scale ones. Therefore, multi-scale analysis can help us understand the earthquake rupture process thoroughly from larger scale to smaller scale. By the use of wavelet transform, the wavelet-domain methods can analyze both the time and frequency information of signals in different scales. Traditional wavelet-domain methods (e.g., Ji et al., 2002) implement finite fault inversion with both lower and higher frequency signals together to recover larger-scale and smaller-scale characteristics of the rupture process simultaneously. Here we propose an alternative strategy with a two-step procedure, i.e., firstly constraining the larger-scale characteristics with lower frequency signals, and then resolving the smaller-scale ones with higher frequency signals. We have designed some synthetic tests to testify our strategy and compare it with the traditional one. We also have applied our strategy to study the 2015 Gorkha Nepal earthquake using tele-seismic waveforms. Both the traditional method and our two-step strategy only analyze the data in different temporal scales (i.e., different frequency bands), while the spatial distribution of model parameters also shows multi-scale characteristics. A more sophisticated strategy is to transfer the slip model into different spatial scales, and then analyze the smooth slip distribution (larger scales) with lower frequency data firstly and more detailed slip distribution (smaller scales) with higher frequency data subsequently. We are now implementing the slip inversion using both spatial and temporal domain wavelets. This multi-scale analysis can help us better understand frequency-dependent rupture characteristics of large earthquakes.

Spatial auditory processing in pinnipeds

NASA Astrophysics Data System (ADS)

Holt, Marla M.

Given the biological importance of sound for a variety of activities, pinnipeds must be able to obtain spatial information about their surroundings thorough acoustic input in the absence of other sensory cues. The three chapters of this dissertation address spatial auditory processing capabilities of pinnipeds in air given that these amphibious animals use acoustic signals for reproduction and survival on land. Two chapters are comparative lab-based studies that utilized psychophysical approaches conducted in an acoustic chamber. Chapter 1 addressed the frequency-dependent sound localization abilities at azimuth of three pinniped species (the harbor seal, Phoca vitulina, the California sea lion, Zalophus californianus, and the northern elephant seal, Mirounga angustirostris). While performances of the sea lion and harbor seal were consistent with the duplex theory of sound localization, the elephant seal, a low-frequency hearing specialist, showed a decreased ability to localize the highest frequencies tested. In Chapter 2 spatial release from masking (SRM), which occurs when a signal and masker are spatially separated resulting in improvement in signal detectability relative to conditions in which they are co-located, was determined in a harbor seal and sea lion. Absolute and masked thresholds were measured at three frequencies and azimuths to determine the detection advantages afforded by this type of spatial auditory processing. Results showed that hearing sensitivity was enhanced by up to 19 and 12 dB in the harbor seal and sea lion, respectively, when the signal and masker were spatially separated. Chapter 3 was a field-based study that quantified both sender and receiver variables of the directional properties of male northern elephant seal calls produce within communication system that serves to delineate dominance status. This included measuring call directivity patterns, observing male-male vocally-mediated interactions, and an acoustic playback study. Results showed that males produce calls that were highly directional that together with social status influenced the response of receivers. Results from the playback study were able to confirm that the isolated acoustic components of this display resulted in similar responses among males. These three chapters provide further information about comparative aspects of spatial auditory processing in pinnipeds.

A discrepancy within primate spatial vision and its bearing on the definition of edge detection processes in machine vision

NASA Technical Reports Server (NTRS)

Jobson, Daniel J.

1990-01-01

The visual perception of form information is considered to be based on the functioning of simple and complex neurons in the primate striate cortex. However, a review of the physiological data on these brain cells cannot be harmonized with either the perceptual spatial frequency performance of primates or the performance which is necessary for form perception in humans. This discrepancy together with recent interest in cortical-like and perceptual-like processing in image coding and machine vision prompted a series of image processing experiments intended to provide some definition of the selection of image operators. The experiments were aimed at determining operators which could be used to detect edges in a computational manner consistent with the visual perception of structure in images. Fundamental issues were the selection of size (peak spatial frequency) and circular versus oriented operators (or some combination). In a previous study, circular difference-of-Gaussian (DOG) operators, with peak spatial frequency responses at about 11 and 33 cyc/deg were found to capture the primary structural information in images. Here larger scale circular DOG operators were explored and led to severe loss of image structure and introduced spatial dislocations (due to blur) in structure which is not consistent with visual perception. Orientation sensitive operators (akin to one class of simple cortical neurons) introduced ambiguities of edge extent regardless of the scale of the operator. For machine vision schemes which are functionally similar to natural vision form perception, two circularly symmetric very high spatial frequency channels appear to be necessary and sufficient for a wide range of natural images. Such a machine vision scheme is most similar to the physiological performance of the primate lateral geniculate nucleus rather than the striate cortex.

Real-Time Optical Image Processing Techniques

DTIC Science & Technology

1988-10-31

pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the modification of micro-chan- nel spatial...required for non-linear operation. Real-time nonlinear processing was performed using the halftone screen and MSLM. The experiments showed the effectiveness...pulse frequency modulation has been pursued through the analysis, design, and fabrication of pulse frequency modulated halftone screens and the

Top-Down Beta Enhances Bottom-Up Gamma

PubMed Central

Thompson, William H.

2017-01-01

Several recent studies have demonstrated that the bottom-up signaling of a visual stimulus is subserved by interareal gamma-band synchronization, whereas top-down influences are mediated by alpha-beta band synchronization. These processes may implement top-down control of stimulus processing if top-down and bottom-up mediating rhythms are coupled via cross-frequency interaction. To test this possibility, we investigated Granger-causal influences among awake macaque primary visual area V1, higher visual area V4, and parietal control area 7a during attentional task performance. Top-down 7a-to-V1 beta-band influences enhanced visually driven V1-to-V4 gamma-band influences. This enhancement was spatially specific and largest when beta-band activity preceded gamma-band activity by ∼0.1 s, suggesting a causal effect of top-down processes on bottom-up processes. We propose that this cross-frequency interaction mechanistically subserves the attentional control of stimulus selection. SIGNIFICANCE STATEMENT Contemporary research indicates that the alpha-beta frequency band underlies top-down control, whereas the gamma-band mediates bottom-up stimulus processing. This arrangement inspires an attractive hypothesis, which posits that top-down beta-band influences directly modulate bottom-up gamma band influences via cross-frequency interaction. We evaluate this hypothesis determining that beta-band top-down influences from parietal area 7a to visual area V1 are correlated with bottom-up gamma frequency influences from V1 to area V4, in a spatially specific manner, and that this correlation is maximal when top-down activity precedes bottom-up activity. These results show that for top-down processes such as spatial attention, elevated top-down beta-band influences directly enhance feedforward stimulus-induced gamma-band processing, leading to enhancement of the selected stimulus. PMID:28592697

A 3D THz image processing methodology for a fully integrated, semi-automatic and near real-time operational system

NASA Astrophysics Data System (ADS)

Brook, A.; Cristofani, E.; Vandewal, M.; Matheis, C.; Jonuscheit, J.; Beigang, R.

2012-05-01

The present study proposes a fully integrated, semi-automatic and near real-time mode-operated image processing methodology developed for Frequency-Modulated Continuous-Wave (FMCW) THz images with the center frequencies around: 100 GHz and 300 GHz. The quality control of aeronautics composite multi-layered materials and structures using Non-Destructive Testing is the main focus of this work. Image processing is applied on the 3-D images to extract useful information. The data is processed by extracting areas of interest. The detected areas are subjected to image analysis for more particular investigation managed by a spatial model. Finally, the post-processing stage examines and evaluates the spatial accuracy of the extracted information.

Advanced Image Processing Techniques for Maximum Information Recovery

DTIC Science & Technology

2006-11-01

0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision...available information from an image. Some radio frequency and optical sensors collect large-scale sets of spatial imagery data whose content is often...Some radio frequency and optical sensors collect large- scale sets of spatial imagery data whose content is often obscured by fog, clouds, foliage

Lost in the Forest, Stuck in the Trees: Dispositional Global/Local Bias Is Resistant to Exposure to High and Low Spatial Frequencies

PubMed Central

Dale, Gillian; Arnell, Karen M.

2014-01-01

Visual stimuli can be perceived at a broad, “global” level, or at a more focused, “local” level. While research has shown that many individuals demonstrate a preference for global information, there are large individual differences in the degree of global/local bias, such that some individuals show a large global bias, some show a large local bias, and others show no bias. The main purpose of the current study was to examine whether these dispositional differences in global/local bias could be altered through various manipulations of high/low spatial frequency. Through 5 experiments, we examined various measures of dispositional global/local bias and whether performance on these measures could be altered by manipulating previous exposure to high or low spatial frequency information (with high/low spatial frequency faces, gratings, and Navon letters). Ultimately, there was little evidence of change from pre-to-post manipulation on the dispositional measures, and dispositional global/local bias was highly reliable pre- to post-manipulation. The results provide evidence that individual differences in global/local bias or preference are relatively resistant to exposure to spatial frequency information, and suggest that the processing mechanisms underlying high/low spatial frequency use and global/local bias may be more independent than previously thought. PMID:24992321

Anorexia nervosa and body dysmorphic disorder are associated with abnormalities in processing visual information.

PubMed

Li, W; Lai, T M; Bohon, C; Loo, S K; McCurdy, D; Strober, M; Bookheimer, S; Feusner, J

2015-07-01

Anorexia nervosa (AN) and body dysmorphic disorder (BDD) are characterized by distorted body image and are frequently co-morbid with each other, although their relationship remains little studied. While there is evidence of abnormalities in visual and visuospatial processing in both disorders, no study has directly compared the two. We used two complementary modalities--event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI)--to test for abnormal activity associated with early visual signaling. We acquired fMRI and ERP data in separate sessions from 15 unmedicated individuals in each of three groups (weight-restored AN, BDD, and healthy controls) while they viewed images of faces and houses of different spatial frequencies. We used joint independent component analyses to compare activity in visual systems. AN and BDD groups demonstrated similar hypoactivity in early secondary visual processing regions and the dorsal visual stream when viewing low spatial frequency faces, linked to the N170 component, as well as in early secondary visual processing regions when viewing low spatial frequency houses, linked to the P100 component. Additionally, the BDD group exhibited hyperactivity in fusiform cortex when viewing high spatial frequency houses, linked to the N170 component. Greater activity in this component was associated with lower attractiveness ratings of faces. Results provide preliminary evidence of similar abnormal spatiotemporal activation in AN and BDD for configural/holistic information for appearance- and non-appearance-related stimuli. This suggests a common phenotype of abnormal early visual system functioning, which may contribute to perceptual distortions.

Hybrid Discrete Wavelet Transform and Gabor Filter Banks Processing for Features Extraction from Biomedical Images

PubMed Central

Lahmiri, Salim; Boukadoum, Mounir

2013-01-01

A new methodology for automatic feature extraction from biomedical images and subsequent classification is presented. The approach exploits the spatial orientation of high-frequency textural features of the processed image as determined by a two-step process. First, the two-dimensional discrete wavelet transform (DWT) is applied to obtain the HH high-frequency subband image. Then, a Gabor filter bank is applied to the latter at different frequencies and spatial orientations to obtain new Gabor-filtered image whose entropy and uniformity are computed. Finally, the obtained statistics are fed to a support vector machine (SVM) binary classifier. The approach was validated on mammograms, retina, and brain magnetic resonance (MR) images. The obtained classification accuracies show better performance in comparison to common approaches that use only the DWT or Gabor filter banks for feature extraction. PMID:27006906

Detection and recognition of simple spatial forms

NASA Technical Reports Server (NTRS)

Watson, A. B.

1983-01-01

A model of human visual sensitivity to spatial patterns is constructed. The model predicts the visibility and discriminability of arbitrary two-dimensional monochrome images. The image is analyzed by a large array of linear feature sensors, which differ in spatial frequency, phase, orientation, and position in the visual field. All sensors have one octave frequency bandwidths, and increase in size linearly with eccentricity. Sensor responses are processed by an ideal Bayesian classifier, subject to uncertainty. The performance of the model is compared to that of the human observer in detecting and discriminating some simple images.

Efficient visual object and word recognition relies on high spatial frequency coding in the left posterior fusiform gyrus: evidence from a case-series of patients with ventral occipito-temporal cortex damage.

PubMed

Roberts, Daniel J; Woollams, Anna M; Kim, Esther; Beeson, Pelagie M; Rapcsak, Steven Z; Lambon Ralph, Matthew A

2013-11-01

Recent visual neuroscience investigations suggest that ventral occipito-temporal cortex is retinotopically organized, with high acuity foveal input projecting primarily to the posterior fusiform gyrus (pFG), making this region crucial for coding high spatial frequency information. Because high spatial frequencies are critical for fine-grained visual discrimination, we hypothesized that damage to the left pFG should have an adverse effect not only on efficient reading, as observed in pure alexia, but also on the processing of complex non-orthographic visual stimuli. Consistent with this hypothesis, we obtained evidence that a large case series (n = 20) of patients with lesions centered on left pFG: 1) Exhibited reduced sensitivity to high spatial frequencies; 2) demonstrated prolonged response latencies both in reading (pure alexia) and object naming; and 3) were especially sensitive to visual complexity and similarity when discriminating between novel visual patterns. These results suggest that the patients' dual reading and non-orthographic recognition impairments have a common underlying mechanism and reflect the loss of high spatial frequency visual information normally coded in the left pFG.

The edge of awareness: Mask spatial density, but not color, determines optimal temporal frequency for continuous flash suppression.

PubMed

Drewes, Jan; Zhu, Weina; Melcher, David

2018-01-01

The study of how visual processing functions in the absence of visual awareness has become a major research interest in the vision-science community. One of the main sources of evidence that stimuli that do not reach conscious awareness-and are thus "invisible"-are still processed to some degree by the visual system comes from studies using continuous flash suppression (CFS). Why and how CFS works may provide more general insight into how stimuli access awareness. As spatial and temporal properties of stimuli are major determinants of visual perception, we hypothesized that these properties of the CFS masks would be of significant importance to the achieved suppression depth. In previous studies however, the spatial and temporal properties of the masks themselves have received little study, and masking parameters vary widely across studies, making a metacomparison difficult. To investigate the factors that determine the effectiveness of CFS, we varied both the temporal frequency and the spatial density of Mondrian-style masks. We consistently found the longest suppression duration for a mask temporal frequency of around 6 Hz. In trials using masks with reduced spatial density, suppression was weaker and frequency tuning was less precise. In contrast, removing color reduced mask effectiveness but did not change the pattern of suppression strength as a function of frequency. Overall, this pattern of results stresses the importance of CFS mask parameters and is consistent with the idea that CFS works by disrupting the spatiotemporal mechanisms that underlie conscious access to visual input.

Faster processing of multiple spatially-heterodyned direct to digital holograms

DOEpatents

Hanson, Gregory R.; Bingham, Philip R.

2006-10-03

Systems and methods are described for faster processing of multiple spatially-heterodyned direct to digital holograms. A method includes of obtaining multiple spatially-heterodyned holograms, includes: digitally recording a first spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis; digitally recording a second spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis; Fourier analyzing the recorded first spatially-heterodyned hologram by shifting a first original origin of the recorded first spatially-heterodyned hologram including spatial heterodyne fringes in Fourier space to sit on top of a spatial-heterodyne carrier frequency defined as a first angle between a first reference beam and a first, object beam; applying a first digital filter to cut off signals around the first original origin and performing an inverse Fourier transform on the result; Fourier analyzing the recorded second spatially-heterodyned hologram by shifting a second original origin of the recorded second spatially-heterodyned hologram including spatial heterodyne fringes in Fourier space to sit on top of a spatial-heterodyne carrier frequency defined as a second angle between a second reference beam and a second object beam; and applying a second digital filter to cut off signals around the second original origin and performing an inverse Fourier transform on the result, wherein digitally recording the first spatially-heterodyned hologram is completed before digitally recording the second spatially-heterodyned hologram and a single digital image includes both the first spatially-heterodyned hologram and the second spatially-heterodyned hologram.

Faster processing of multiple spatially-heterodyned direct to digital holograms

DOEpatents

Hanson, Gregory R [Clinton, TN; Bingham, Philip R [Knoxville, TN

2008-09-09

Systems and methods are described for faster processing of multiple spatially-heterodyned direct to digital holograms. A method includes of obtaining multiple spatially-heterodyned holograms, includes: digitally recording a first spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis; digitally recording a second spatially-heterodyned hologram including spatial heterodyne fringes for Fourier analysis; Fourier analyzing the recorded first spatially-heterodyned hologram by shifting a first original origin of the recorded first spatially-heterodyned hologram including spatial heterodyne fringes in Fourier space to sit on top of a spatial-heterodyne carrier frequency defined as a first angle between a first reference beam and a first object beam; applying a first digital filter to cut off signals around the first original origin and performing an inverse Fourier transform on the result; Fourier analyzing the recorded second spatially-heterodyned hologram by shifting a second original origin of the recorded second spatially-heterodyned hologram including spatial heterodyne fringes in Fourier space to sit on top of a spatial-heterodyne carrier frequency defined as a second angle between a second reference beam and a second object beam; and applying a second digital filter to cut off signals around the second original origin and performing an inverse Fourier transform on the result, wherein digitally recording the first spatially-heterodyned hologram is completed before digitally recording the second spatially-heterodyned hologram and a single digital image includes both the first spatially-heterodyned hologram and the second spatially-heterodyned hologram.

SPECIAL ISSUE ON OPTICAL PROCESSING OF INFORMATION: Optical information processing with transformation of the spatial coherence of light

NASA Astrophysics Data System (ADS)

Bykovskii, Yurii A.; Markilov, A. A.; Rodin, V. G.; Starikov, S. N.

1995-10-01

A description is given of systems with spatially incoherent illumination, intended for spectral and correlation analysis, and for the recording of Fourier holograms. These systems make use of transformation of the degree of the spatial coherence of light. The results are given of the processing of images and signals, including those transmitted by a bundle of fibre-optic waveguides both as monochromatic light and as quasimonochromatic radiation from a cathode-ray tube. The feasibility of spatial frequency filtering and of correlation analysis of images with a bipolar impulse response is considered for systems with spatially incoherent illumination where these tasks are performed by double transformation of the spatial coherence of light. A description is given of experimental systems and the results of image processing are reported.

Deconstruction of spatial integrity in visual stimulus detected by modulation of synchronized activity in cat visual cortex.

PubMed

Zhou, Zhiyi; Bernard, Melanie R; Bonds, A B

2008-04-02

Spatiotemporal relationships among contour segments can influence synchronization of neural responses in the primary visual cortex. We performed a systematic study to dissociate the impact of spatial and temporal factors in the signaling of contour integration via synchrony. In addition, we characterized the temporal evolution of this process to clarify potential underlying mechanisms. With a 10 x 10 microelectrode array, we recorded the simultaneous activity of multiple cells in the cat primary visual cortex while stimulating with drifting sine-wave gratings. We preserved temporal integrity and systematically degraded spatial integrity of the sine-wave gratings by adding spatial noise. Neural synchronization was analyzed in the time and frequency domains by conducting cross-correlation and coherence analyses. The general association between neural spike trains depends strongly on spatial integrity, with coherence in the gamma band (35-70 Hz) showing greater sensitivity to the change of spatial structure than other frequency bands. Analysis of the temporal dynamics of synchronization in both time and frequency domains suggests that spike timing synchronization is triggered nearly instantaneously by coherent structure in the stimuli, whereas frequency-specific oscillatory components develop more slowly, presumably through network interactions. Our results suggest that, whereas temporal integrity is required for the generation of synchrony, spatial integrity is critical in triggering subsequent gamma band synchronization.

A Rapid Subcortical Amygdala Route for Faces Irrespective of Spatial Frequency and Emotion.

PubMed

McFadyen, Jessica; Mermillod, Martial; Mattingley, Jason B; Halász, Veronika; Garrido, Marta I

2017-04-05

There is significant controversy over the existence and function of a direct subcortical visual pathway to the amygdala. It is thought that this pathway rapidly transmits low spatial frequency information to the amygdala independently of the cortex, and yet the directionality of this function has never been determined. We used magnetoencephalography to measure neural activity while human participants discriminated the gender of neutral and fearful faces filtered for low or high spatial frequencies. We applied dynamic causal modeling to demonstrate that the most likely underlying neural network consisted of a pulvinar-amygdala connection that was uninfluenced by spatial frequency or emotion, and a cortical-amygdala connection that conveyed high spatial frequencies. Crucially, data-driven neural simulations revealed a clear temporal advantage of the subcortical connection over the cortical connection in influencing amygdala activity. Thus, our findings support the existence of a rapid subcortical pathway that is nonselective in terms of the spatial frequency or emotional content of faces. We propose that that the "coarseness" of the subcortical route may be better reframed as "generalized." SIGNIFICANCE STATEMENT The human amygdala coordinates how we respond to biologically relevant stimuli, such as threat or reward. It has been postulated that the amygdala first receives visual input via a rapid subcortical route that conveys "coarse" information, namely, low spatial frequencies. For the first time, the present paper provides direction-specific evidence from computational modeling that the subcortical route plays a generalized role in visual processing by rapidly transmitting raw, unfiltered information directly to the amygdala. This calls into question a widely held assumption across human and animal research that fear responses are produced faster by low spatial frequencies. Our proposed mechanism suggests organisms quickly generate fear responses to a wide range of visual properties, heavily implicating future research on anxiety-prevention strategies. Copyright © 2017 the authors 0270-6474/17/373864-11$15.00/0.

Comparison of Frequency-Domain Array Methods for Studying Earthquake Rupture Process

NASA Astrophysics Data System (ADS)

Sheng, Y.; Yin, J.; Yao, H.

2014-12-01

Seismic array methods, in both time- and frequency- domains, have been widely used to study the rupture process and energy radiation of earthquakes. With better spatial resolution, the high-resolution frequency-domain methods, such as Multiple Signal Classification (MUSIC) (Schimdt, 1986; Meng et al., 2011) and the recently developed Compressive Sensing (CS) technique (Yao et al., 2011, 2013), are revealing new features of earthquake rupture processes. We have performed various tests on the methods of MUSIC, CS, minimum-variance distortionless response (MVDR) Beamforming and conventional Beamforming in order to better understand the advantages and features of these methods for studying earthquake rupture processes. We use the ricker wavelet to synthesize seismograms and use these frequency-domain techniques to relocate the synthetic sources we set, for instance, two sources separated in space but, their waveforms completely overlapping in the time domain. We also test the effects of the sliding window scheme on the recovery of a series of input sources, in particular, some artifacts that are caused by the sliding window scheme. Based on our tests, we find that CS, which is developed from the theory of sparsity inversion, has relatively high spatial resolution than the other frequency-domain methods and has better performance at lower frequencies. In high-frequency bands, MUSIC, as well as MVDR Beamforming, is more stable, especially in the multi-source situation. Meanwhile, CS tends to produce more artifacts when data have poor signal-to-noise ratio. Although these techniques can distinctly improve the spatial resolution, they still produce some artifacts along with the sliding of the time window. Furthermore, we propose a new method, which combines both the time-domain and frequency-domain techniques, to suppress these artifacts and obtain more reliable earthquake rupture images. Finally, we apply this new technique to study the 2013 Okhotsk deep mega earthquake in order to better capture the rupture characteristics (e.g., rupture area and velocity) of this earthquake.

Perceptual Simulations and Linguistic Representations Have Differential Effects on Speeded Relatedness Judgments and Recognition Memory

PubMed Central

Tse, Chi-Shing; Kurby, Christopher A.; Du, Feng

2010-01-01

We examined the effect of spatial iconicity (a perceptual simulation of canonical locations of objects) and word-order frequency on language processing and episodic memory of orientation. Participants made speeded relatedness judgments to pairs of words presented in locations typical to their real world arrangements (e.g., ceiling on top and floor on bottom). They then engaged in a surprise orientation recognition task for the word pairs. We replicated Louwerse’s finding (2008) that word-order frequency has a stronger effect on semantic relatedness judgments than spatial iconicity. This is consistent with recent suggestions that linguistic representations have a stronger impact on immediate decisions about verbal materials than perceptual simulations. In contrast, spatial iconicity enhanced episodic memory of orientation to a greater extent than word-order frequency did. This new finding indicates that perceptual simulations have an important role in episodic memory. Results are discussed with respect to theories of perceptual representation and linguistic processing. PMID:19742388

Evaluate error correction ability of magnetorheological finishing by smoothing spectral function

NASA Astrophysics Data System (ADS)

Wang, Jia; Fan, Bin; Wan, Yongjian; Shi, Chunyan; Zhuo, Bin

2014-08-01

Power Spectral Density (PSD) has been entrenched in optics design and manufacturing as a characterization of mid-high spatial frequency (MHSF) errors. Smoothing Spectral Function (SSF) is a newly proposed parameter that based on PSD to evaluate error correction ability of computer controlled optical surfacing (CCOS) technologies. As a typical deterministic and sub-aperture finishing technology based on CCOS, magnetorheological finishing (MRF) leads to MHSF errors inevitably. SSF is employed to research different spatial frequency error correction ability of MRF process. The surface figures and PSD curves of work-piece machined by MRF are presented. By calculating SSF curve, the correction ability of MRF for different spatial frequency errors will be indicated as a normalized numerical value.

Every photon counts: improving low, mid, and high-spatial frequency errors on astronomical optics and materials with MRF

NASA Astrophysics Data System (ADS)

Maloney, Chris; Lormeau, Jean Pierre; Dumas, Paul

2016-07-01

Many astronomical sensing applications operate in low-light conditions; for these applications every photon counts. Controlling mid-spatial frequencies and surface roughness on astronomical optics are critical for mitigating scattering effects such as flare and energy loss. By improving these two frequency regimes higher contrast images can be collected with improved efficiency. Classically, Magnetorheological Finishing (MRF) has offered an optical fabrication technique to correct low order errors as well has quilting/print-through errors left over in light-weighted optics from conventional polishing techniques. MRF is a deterministic, sub-aperture polishing process that has been used to improve figure on an ever expanding assortment of optical geometries, such as planos, spheres, on and off axis aspheres, primary mirrors and freeform optics. Precision optics are routinely manufactured by this technology with sizes ranging from 5-2,000mm in diameter. MRF can be used for form corrections; turning a sphere into an asphere or free form, but more commonly for figure corrections achieving figure errors as low as 1nm RMS while using careful metrology setups. Recent advancements in MRF technology have improved the polishing performance expected for astronomical optics in low, mid and high spatial frequency regimes. Deterministic figure correction with MRF is compatible with most materials, including some recent examples on Silicon Carbide and RSA905 Aluminum. MRF also has the ability to produce `perfectly-bad' compensating surfaces, which may be used to compensate for measured or modeled optical deformation from sources such as gravity or mounting. In addition, recent advances in MRF technology allow for corrections of mid-spatial wavelengths as small as 1mm simultaneously with form error correction. Efficient midspatial frequency corrections make use of optimized process conditions including raster polishing in combination with a small tool size. Furthermore, a novel MRF fluid, called C30, has been developed to finish surfaces to ultra-low roughness (ULR) and has been used as the low removal rate fluid required for fine figure correction of mid-spatial frequency errors. This novel MRF fluid is able to achieve <4Å RMS on Nickel-plated Aluminum and even <1.5Å RMS roughness on Silicon, Fused Silica and other materials. C30 fluid is best utilized within a fine figure correction process to target mid-spatial frequency errors as well as smooth surface roughness 'for free' all in one step. In this paper we will discuss recent advancements in MRF technology and the ability to meet requirements for precision optics in low, mid and high spatial frequency regimes and how improved MRF performance addresses the need for achieving tight specifications required for astronomical optics.

Testing the generality of the zoom-lens model: Evidence for visual-pathway specific effects of attended-region size on perception.

PubMed

Goodhew, Stephanie C; Lawrence, Rebecca K; Edwards, Mark

2017-05-01

There are volumes of information available to process in visual scenes. Visual spatial attention is a critically important selection mechanism that prevents these volumes from overwhelming our visual system's limited-capacity processing resources. We were interested in understanding the effect of the size of the attended area on visual perception. The prevailing model of attended-region size across cognition, perception, and neuroscience is the zoom-lens model. This model stipulates that the magnitude of perceptual processing enhancement is inversely related to the size of the attended region, such that a narrow attended-region facilitates greater perceptual enhancement than a wider region. Yet visual processing is subserved by two major visual pathways (magnocellular and parvocellular) that operate with a degree of independence in early visual processing and encode contrasting visual information. Historically, testing of the zoom-lens has used measures of spatial acuity ideally suited to parvocellular processing. This, therefore, raises questions about the generality of the zoom-lens model to different aspects of visual perception. We found that while a narrow attended-region facilitated spatial acuity and the perception of high spatial frequency targets, it had no impact on either temporal acuity or the perception of low spatial frequency targets. This pattern also held up when targets were not presented centrally. This supports the notion that visual attended-region size has dissociable effects on magnocellular versus parvocellular mediated visual processing.

Combining Temporal and Spectral Information with Spatial Mapping to Identify Differences between Phonological and Semantic Networks: A Magnetoencephalographic Approach.

PubMed

McNab, Fiona; Hillebrand, Arjan; Swithenby, Stephen J; Rippon, Gina

2012-01-01

Early, lesion-based models of language processing suggested that semantic and phonological processes are associated with distinct temporal and parietal regions respectively, with frontal areas more indirectly involved. Contemporary spatial brain mapping techniques have not supported such clear-cut segregation, with strong evidence of activation in left temporal areas by both processes and disputed evidence of involvement of frontal areas in both processes. We suggest that combining spatial information with temporal and spectral data may allow a closer scrutiny of the differential involvement of closely overlapping cortical areas in language processing. Using beamforming techniques to analyze magnetoencephalography data, we localized the neuronal substrates underlying primed responses to nouns requiring either phonological or semantic processing, and examined the associated measures of time and frequency in those areas where activation was common to both tasks. Power changes in the beta (14-30 Hz) and gamma (30-50 Hz) frequency bands were analyzed in pre-selected time windows of 350-550 and 500-700 ms In left temporal regions, both tasks elicited power changes in the same time window (350-550 ms), but with different spectral characteristics, low beta (14-20 Hz) for the phonological task and high beta (20-30 Hz) for the semantic task. In frontal areas (BA10), both tasks elicited power changes in the gamma band (30-50 Hz), but in different time windows, 500-700 ms for the phonological task and 350-550 ms for the semantic task. In the left inferior parietal area (BA40), both tasks elicited changes in the 20-30 Hz beta frequency band but in different time windows, 350-550 ms for the phonological task and 500-700 ms for the semantic task. Our findings suggest that, where spatial measures may indicate overlapping areas of involvement, additional beamforming techniques can demonstrate differential activation in time and frequency domains.

Observations on the effects of image processing functions on fingermark data in the Fourier domain

NASA Astrophysics Data System (ADS)

Bramble, Simon K.; Fabrizi, Paola M.

1995-09-01

One of the image processing functions used for the enhancement of laten fingermark images is the Fourier transform. This paper describes some effects of spatial resolution, zero-filling and windowing on fingermark data in the Fourier domain. It is shown that with an understanding of the fingermark structure it is possible to determine the approximate prosition of the frequency data in the Fourier domain corresponding to the fingermark image detail. The effect of attenuation of frequency data on a zero-filled image is shown to be different to the same attenuation on a non-zero-filled image. The effects of windowing spatial data on the frequency data are also highlighted and compared with the same data after the application of a Hanning window.

The Role of Global and Local Visual Information during Gaze-Cued Orienting of Attention.

PubMed

Munsters, Nicolette M; van den Boomen, Carlijn; Hooge, Ignace T C; Kemner, Chantal

2016-01-01

Gaze direction is an important social communication tool. Global and local visual information are known to play specific roles in processing socially relevant information from a face. The current study investigated whether global visual information has a primary role during gaze-cued orienting of attention and, as such, may influence quality of interaction. Adults performed a gaze-cueing task in which a centrally presented face cued (valid or invalid) the location of a peripheral target through a gaze shift. We measured brain activity (electroencephalography) towards the cue and target and behavioral responses (manual and saccadic reaction times) towards the target. The faces contained global (i.e. lower spatial frequencies), local (i.e. higher spatial frequencies), or a selection of both global and local (i.e. mid-band spatial frequencies) visual information. We found a gaze cue-validity effect (i.e. valid versus invalid), but no interaction effects with spatial frequency content. Furthermore, behavioral responses towards the target were in all cue conditions slower when lower spatial frequencies were not present in the gaze cue. These results suggest that whereas gaze-cued orienting of attention can be driven by both global and local visual information, global visual information determines the speed of behavioral responses towards other entities appearing in the surrounding of gaze cue stimuli.

Binocular rivalry after right-hemisphere stroke: Effects of attention impairment on perceptual dominance patterns.

PubMed

Walle, Kjersti Mæhlum; Kyler, Hillary Lynn; Nordvik, Jan Egil; Becker, Frank; Laeng, Bruno

2017-10-01

Binocular rivalry is when perception fluctuates while the stimuli, consisting of different images presented to each eye, remain unchanged. The fluctuation rate and predominance ratio of these images are regarded as information source for understanding properties of consciousness and perception. We administered a binocular rivalry task to 26 right-hemisphere stroke patients and 26 healthy control participants, using stimuli such as simple Gabor anaglyphs. Each single Gabor image was of unequal spatial frequency compared to its counterpart, allowing assessment of the effect of relative spatial frequency on rivalry predominance. Results revealed that patients had significantly decreased alternation rate compared to healthy controls, with severity of patients' attention impairment predicting alternation rates. The patient group had higher predominance ratio for high compared to low relative spatial frequency stimuli consistent with the hypothesis that damage to the right hemisphere may disrupt processing of relatively low spatial frequencies. Degree of attention impairment also predicted the effect of relative spatial frequencies. Lastly, both groups showed increased predominance rates in the right eye compared to the left eye. This right eye dominance was more pronounced in patients than controls, suggesting that right hemisphere stroke may additionally affect eye predominance ratios. Copyright © 2017 Elsevier Inc. All rights reserved.

Exploiting spectral content for image segmentation in GPR data

NASA Astrophysics Data System (ADS)

Wang, Patrick K.; Morton, Kenneth D., Jr.; Collins, Leslie M.; Torrione, Peter A.

2011-06-01

Ground-penetrating radar (GPR) sensors provide an effective means for detecting changes in the sub-surface electrical properties of soils, such as changes indicative of landmines or other buried threats. However, most GPR-based pre-screening algorithms only localize target responses along the surface of the earth, and do not provide information regarding an object's position in depth. As a result, feature extraction algorithms are forced to process data from entire cubes of data around pre-screener alarms, which can reduce feature fidelity and hamper performance. In this work, spectral analysis is investigated as a method for locating subsurface anomalies in GPR data. In particular, a 2-D spatial/frequency decomposition is applied to pre-screener flagged GPR B-scans. Analysis of these spatial/frequency regions suggests that aspects (e.g. moments, maxima, mode) of the frequency distribution of GPR energy can be indicative of the presence of target responses. After translating a GPR image to a function of the spatial/frequency distributions at each pixel, several image segmentation approaches can be applied to perform segmentation in this new transformed feature space. To illustrate the efficacy of the approach, a performance comparison between feature processing with and without the image segmentation algorithm is provided.

Calibration of a spatial light modulator containing dual frequency liquid crystal

NASA Astrophysics Data System (ADS)

Gu, Dong-Feng; Winker, Bruce; Wen, Bing; Taber, Don; Brackley, Andrew; Wirth, Allan; Albanese, Marc; Landers, Frank

2005-08-01

Characterization and calibration process for a liquid crystal (LC) spatial light modulator (SLM) containing dual frequency liquid crystal is described. Special care was taken when dealing with LC cell gap non-uniformity and defect pixels. The calibration results were fed into a closed loop control algorithm to demonstrate correction of wavefront distortions. The performance characteristics of the device were reported. Substantial improvements were made in speed (bandwidth), resolution, power consumption and system weight/volume.

Orientation tuning of binocular summation: a comparison of colour to achromatic contrast

PubMed Central

Gheiratmand, Mina; Cherniawsky, Avital S.; Mullen, Kathy T.

2016-01-01

A key function of the primary visual cortex is to combine the input from the two eyes into a unified binocular percept. At low, near threshold, contrasts a process of summation occurs if the visual inputs from the two eyes are similar. Here we measure the orientation tuning of binocular summation for chromatic and equivalent achromatic contrast. We derive estimates of orientation tuning by measuring binocular summation as a function of the orientation difference between two sinusoidal gratings presented dichoptically to different eyes. We then use a model to estimate the orientation bandwidth of the neural detectors underlying the binocular combination. We find that orientation bandwidths are similar for chromatic and achromatic stimuli at both low (0.375 c/deg) and mid (1.5 c/deg) spatial frequencies, with an overall average of 29 ± 3 degs (HWHH, s.e.m). This effect occurs despite the overall greater binocular summation found for the low spatial frequency chromatic stimuli. These results suggest that similar, oriented processes underlie both chromatic and achromatic binocular contrast combination. The non-oriented detection process found in colour vision at low spatial frequencies under monocular viewing is not evident at the binocular combination stage. PMID:27168119

Multi-mode of Four and Six Wave Parametric Amplified Process

NASA Astrophysics Data System (ADS)

Zhu, Dayu; Yang, Yiheng; Zhang, Da; Liu, Ruizhou; Ma, Danmeng; Li, Changbiao; Zhang, Yanpeng

2017-03-01

Multiple quantum modes in correlated fields are essential for future quantum information processing and quantum computing. Here we report the generation of multi-mode phenomenon through parametric amplified four- and six-wave mixing processes in a rubidium atomic ensemble. The multi-mode properties in both frequency and spatial domains are studied. On one hand, the multi-mode behavior is dominantly controlled by the intensity of external dressing effect, or nonlinear phase shift through internal dressing effect, in frequency domain; on the other hand, the multi-mode behavior is visually demonstrated from the images of the biphoton fields directly, in spatial domain. Besides, the correlation of the two output fields is also demonstrated in both domains. Our approach supports efficient applications for scalable quantum correlated imaging.

Multi-mode of Four and Six Wave Parametric Amplified Process.

PubMed

Zhu, Dayu; Yang, Yiheng; Zhang, Da; Liu, Ruizhou; Ma, Danmeng; Li, Changbiao; Zhang, Yanpeng

2017-03-03

Multiple quantum modes in correlated fields are essential for future quantum information processing and quantum computing. Here we report the generation of multi-mode phenomenon through parametric amplified four- and six-wave mixing processes in a rubidium atomic ensemble. The multi-mode properties in both frequency and spatial domains are studied. On one hand, the multi-mode behavior is dominantly controlled by the intensity of external dressing effect, or nonlinear phase shift through internal dressing effect, in frequency domain; on the other hand, the multi-mode behavior is visually demonstrated from the images of the biphoton fields directly, in spatial domain. Besides, the correlation of the two output fields is also demonstrated in both domains. Our approach supports efficient applications for scalable quantum correlated imaging.

Computational models of human vision with applications

NASA Technical Reports Server (NTRS)

Wandell, B. A.

1985-01-01

Perceptual problems in aeronautics were studied. The mechanism by which color constancy is achieved in human vision was examined. A computable algorithm was developed to model the arrangement of retinal cones in spatial vision. The spatial frequency spectra are similar to the spectra of actual cone mosaics. The Hartley transform as a tool of image processing was evaluated and it is suggested that it could be used in signal processing applications, GR image processing.

New prototype of acousto-optical radio-wave spectrometer with parallel frequency processing for astrophysical applications

NASA Astrophysics Data System (ADS)

Shcherbakov, Alexandre S.; Chavez Dagostino, Miguel; Arellanes, Adan O.; Aguirre Lopez, Arturo

2016-09-01

We develop a multi-band spectrometer with a few spatially parallel optical arms for the combined processing of their data flow. Such multi-band capability has various applications in astrophysical scenarios at different scales: from objects in the distant universe to planetary atmospheres in the Solar system. Each optical arm exhibits original performances to provide parallel multi-band observations with different scales simultaneously. Similar possibility is based on designing each optical arm individually via exploiting different materials for acousto-optical cells operating within various regimes, frequency ranges and light wavelengths from independent light sources. Individual beam shapers provide both the needed incident light polarization and the required apodization to increase the dynamic range of a system. After parallel acousto-optical processing, data flows are united by the joint CCD matrix on the stage of the combined electronic data processing. At the moment, the prototype combines still three bands, i.e. includes three spatial optical arms. The first low-frequency arm operates at the central frequencies 60-80 MHz with frequency bandwidth 40 MHz. The second arm is oriented to middle-frequencies 350-500 MHz with frequency bandwidth 200-300 MHz. The third arm is intended for ultra-high-frequency radio-wave signals about 1.0-1.5 GHz with frequency bandwidth <300 MHz. To-day, this spectrometer has the following preliminary performances. The first arm exhibits frequency resolution 20 KHz; while the second and third arms give the resolution 150-200 KHz. The numbers of resolvable spots are 1500- 2000 depending on the regime of operation. The fourth optical arm at the frequency range 3.5 GHz is currently under construction.

Power spectra comparison between GOLF and spatially masked MDI velocity signals

NASA Astrophysics Data System (ADS)

Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.; Bush, R. I.; Scherrer, P. H.; Cortés, T. Roca; Turck-Chièze, S.

1999-08-01

The Global Oscillations at Low Frequency (GOLF) and the Michelson Doppler Imager (MDI) instruments aboard the Solar and Heliospheric Observatory (SOHO) give an excellent opportunity to search for solar low frequency oscillation modes previously undetected from ground based experiments. Presented here is a comparison of the velocity power spectra between the two instruments. In addition, this paper outlines work towards creating a GOLF-simulated signal utilizing MDI velocity images. The simulation of the GOLF signal is achieved by integrating spatially weighted masks with MDI full-disk Doppler images. The GOLF-simulated signal and a selection of additional spatially masked MDI velocity signals are compared with the observed GOLF signal for a 759 day period from May 25, 1996 through June 22, 1998. Ultimately, a cross-analysis process between GOLF and MDI signals could lead to an enhancement of our ability to detect low frequency solar oscillations. For low degree (l<= 3) and low frequency acoustic modes, the signal-to-background ratio between GOLF and the spatially masked MDI velocity data is compared here.

Combined fabrication technique for high-precision aspheric optical windows

NASA Astrophysics Data System (ADS)

Hu, Hao; Song, Ci; Xie, Xuhui

2016-07-01

Specifications made on optical components are becoming more and more stringent with the performance improvement of modern optical systems. These strict requirements not only involve low spatial frequency surface accuracy, mid-and-high spatial frequency surface errors, but also surface smoothness and so on. This presentation mainly focuses on the fabrication process for square aspheric window which combines accurate grinding, magnetorheological finishing (MRF) and smoothing polishing (SP). In order to remove the low spatial frequency surface errors and subsurface defects after accurate grinding, the deterministic polishing method MRF with high convergence and stable material removal rate is applied. Then the SP technology with pseudo-random path is adopted to eliminate the mid-and-high spatial frequency surface ripples and high slope errors which is the defect for MRF. Additionally, the coordinate measurement method and interferometry are combined in different phase. Acid-etched method and ion beam figuring (IBF) are also investigated on observing and reducing the subsurface defects. Actual fabrication result indicates that the combined fabrication technique can lead to high machining efficiency on manufaturing the high-precision and high-quality optical aspheric windows.

Attentional selection of relative SF mediates global versus local processing: evidence from EEG.

PubMed

Flevaris, Anastasia V; Bentin, Shlomo; Robertson, Lynn C

2011-06-13

Previous research on functional hemispheric differences in visual processing has associated global perception with low spatial frequency (LSF) processing biases of the right hemisphere (RH) and local perception with high spatial frequency (HSF) processing biases of the left hemisphere (LH). The Double Filtering by Frequency (DFF) theory expanded this hypothesis by proposing that visual attention selects and is directed to relatively LSFs by the RH and relatively HSFs by the LH, suggesting a direct causal relationship between SF selection and global versus local perception. We tested this idea in the current experiment by comparing activity in the EEG recorded at posterior right and posterior left hemisphere sites while participants' attention was directed to global or local levels of processing after selection of relatively LSFs versus HSFs in a previous stimulus. Hemispheric asymmetry in the alpha band (8-12 Hz) during preparation for global versus local processing was modulated by the selected SF. In contrast, preparatory activity associated with selection of SF was not modulated by the previously attended level (global/local). These results support the DFF theory that top-down attentional selection of SF mediates global and local processing.

Evidence for Separate Contributions of High and Low Spatial Frequencies during Visual Word Recognition.

PubMed

Winsler, Kurt; Holcomb, Phillip J; Midgley, Katherine J; Grainger, Jonathan

2017-01-01

Previous studies have shown that different spatial frequency information processing streams interact during the recognition of visual stimuli. However, it is a matter of debate as to the contributions of high and low spatial frequency (HSF and LSF) information for visual word recognition. This study examined the role of different spatial frequencies in visual word recognition using event-related potential (ERP) masked priming. EEG was recorded from 32 scalp sites in 30 English-speaking adults in a go/no-go semantic categorization task. Stimuli were white characters on a neutral gray background. Targets were uppercase five letter words preceded by a forward-mask (#######) and a 50 ms lowercase prime. Primes were either the same word (repeated) or a different word (un-repeated) than the subsequent target and either contained only high, only low, or full spatial frequency information. Additionally within each condition, half of the prime-target pairs were high lexical frequency, and half were low. In the full spatial frequency condition, typical ERP masked priming effects were found with an attenuated N250 (sub-lexical) and N400 (lexical-semantic) for repeated compared to un-repeated primes. For HSF primes there was a weaker N250 effect which interacted with lexical frequency, a significant reversal of the effect around 300 ms, and an N400-like effect for only high lexical frequency word pairs. LSF primes did not produce any of the classic ERP repetition priming effects, however they did elicit a distinct early effect around 200 ms in the opposite direction of typical repetition effects. HSF information accounted for many of the masked repetition priming ERP effects and therefore suggests that HSFs are more crucial for word recognition. However, LSFs did produce their own pattern of priming effects indicating that larger scale information may still play a role in word recognition.

Differential effects of exogenous and endogenous attention on second-order texture contrast sensitivity

PubMed Central

Barbot, Antoine; Landy, Michael S.; Carrasco, Marisa

2012-01-01

The visual system can use a rich variety of contours to segment visual scenes into distinct perceptually coherent regions. However, successfully segmenting an image is a computationally expensive process. Previously we have shown that exogenous attention—the more automatic, stimulus-driven component of spatial attention—helps extract contours by enhancing contrast sensitivity for second-order, texture-defined patterns at the attended location, while reducing sensitivity at unattended locations, relative to a neutral condition. Interestingly, the effects of exogenous attention depended on the second-order spatial frequency of the stimulus. At parafoveal locations, attention enhanced second-order contrast sensitivity to relatively high, but not to low second-order spatial frequencies. In the present study we investigated whether endogenous attention—the more voluntary, conceptually-driven component of spatial attention—affects second-order contrast sensitivity, and if so, whether its effects are similar to those of exogenous attention. To that end, we compared the effects of exogenous and endogenous attention on the sensitivity to second-order, orientation-defined, texture patterns of either high or low second-order spatial frequencies. The results show that, like exogenous attention, endogenous attention enhances second-order contrast sensitivity at the attended location and reduces it at unattended locations. However, whereas the effects of exogenous attention are a function of the second-order spatial frequency content, endogenous attention affected second-order contrast sensitivity independent of the second-order spatial frequency content. This finding supports the notion that both exogenous and endogenous attention can affect second-order contrast sensitivity, but that endogenous attention is more flexible, benefitting performance under different conditions. PMID:22895879

Quantum image median filtering in the spatial domain

NASA Astrophysics Data System (ADS)

Li, Panchi; Liu, Xiande; Xiao, Hong

2018-03-01

Spatial filtering is one principal tool used in image processing for a broad spectrum of applications. Median filtering has become a prominent representation of spatial filtering because its performance in noise reduction is excellent. Although filtering of quantum images in the frequency domain has been described in the literature, and there is a one-to-one correspondence between linear spatial filters and filters in the frequency domain, median filtering is a nonlinear process that cannot be achieved in the frequency domain. We therefore investigated the spatial filtering of quantum image, focusing on the design method of the quantum median filter and applications in image de-noising. To this end, first, we presented the quantum circuits for three basic modules (i.e., Cycle Shift, Comparator, and Swap), and then, we design two composite modules (i.e., Sort and Median Calculation). We next constructed a complete quantum circuit that implements the median filtering task and present the results of several simulation experiments on some grayscale images with different noise patterns. Although experimental results show that the proposed scheme has almost the same noise suppression capacity as its classical counterpart, the complexity analysis shows that the proposed scheme can reduce the computational complexity of the classical median filter from the exponential function of image size n to the second-order polynomial function of image size n, so that the classical method can be speeded up.

Computer-Controlled Cylindrical Polishing Process for Large X-Ray Mirror Mandrels

NASA Technical Reports Server (NTRS)

Khan, Gufran S.; Gubarev, Mikhail; Speegle, Chet; Ramsey, Brian

2010-01-01

We are developing high-energy grazing incidence shell optics for hard-x-ray telescopes. The resolution of a mirror shells depends on the quality of cylindrical mandrel from which they are being replicated. Mid-spatial-frequency axial figure error is a dominant contributor in the error budget of the mandrel. This paper presents our efforts to develop a deterministic cylindrical polishing process in order to keep the mid-spatial-frequency axial figure errors to a minimum. Simulation software is developed to model the residual surface figure errors of a mandrel due to the polishing process parameters and the tools used, as well as to compute the optical performance of the optics. The study carried out using the developed software was focused on establishing a relationship between the polishing process parameters and the mid-spatial-frequency error generation. The process parameters modeled are the speeds of the lap and the mandrel, the tool s influence function, the contour path (dwell) of the tools, their shape and the distribution of the tools on the polishing lap. Using the inputs from the mathematical model, a mandrel having conical approximated Wolter-1 geometry, has been polished on a newly developed computer-controlled cylindrical polishing machine. The preliminary results of a series of polishing experiments demonstrate a qualitative agreement with the developed model. We report our first experimental results and discuss plans for further improvements in the polishing process. The ability to simulate the polishing process is critical to optimize the polishing process, improve the mandrel quality and significantly reduce the cost of mandrel production

Modes of Visual Recognition and Perceptually Relevant Sketch-based Coding for Images

NASA Technical Reports Server (NTRS)

Jobson, Daniel J.

1991-01-01

A review of visual recognition studies is used to define two levels of information requirements. These two levels are related to two primary subdivisions of the spatial frequency domain of images and reflect two distinct different physical properties of arbitrary scenes. In particular, pathologies in recognition due to cerebral dysfunction point to a more complete split into two major types of processing: high spatial frequency edge based recognition vs. low spatial frequency lightness (and color) based recognition. The former is more central and general while the latter is more specific and is necessary for certain special tasks. The two modes of recognition can also be distinguished on the basis of physical scene properties: the highly localized edges associated with reflectance and sharp topographic transitions vs. smooth topographic undulation. The extreme case of heavily abstracted images is pursued to gain an understanding of the minimal information required to support both modes of recognition. Here the intention is to define the semantic core of transmission. This central core of processing can then be fleshed out with additional image information and coding and rendering techniques.

Priming Facial Gender and Emotional Valence: The Influence of Spatial Frequency on Face Perception in ASD.

PubMed

Vanmarcke, Steven; Wagemans, Johan

2017-04-01

Adolescents with and without autism spectrum disorder (ASD) performed two priming experiments in which they implicitly processed a prime stimulus, containing high and/or low spatial frequency information, and then explicitly categorized a target face either as male/female (gender task) or as positive/negative (Valence task). Adolescents with ASD made more categorization errors than typically developing adolescents. They also showed an age-dependent improvement in categorization speed and had more difficulties with categorizing facial expressions than gender. However, in neither of the categorization tasks, we found group differences in the processing of coarse versus fine prime information. This contradicted our expectations, and indicated that the perceptual differences between adolescents with and without ASD critically depended on the processing time available for the primes.

Joint Estimation of Time-Frequency Signature and DOA Based on STFD for Multicomponent Chirp Signals

PubMed Central

Zhao, Ziyue; Liu, Congfeng

2014-01-01

In the study of the joint estimation of time-frequency signature and direction of arrival (DOA) for multicomponent chirp signals, an estimation method based on spatial time-frequency distributions (STFDs) is proposed in this paper. Firstly, array signal model for multicomponent chirp signals is presented and then array processing is applied in time-frequency analysis to mitigate cross-terms. According to the results of the array processing, Hough transform is performed and the estimation of time-frequency signature is obtained. Subsequently, subspace method for DOA estimation based on STFD matrix is achieved. Simulation results demonstrate the validity of the proposed method. PMID:27382610

Joint Estimation of Time-Frequency Signature and DOA Based on STFD for Multicomponent Chirp Signals.

PubMed

Zhao, Ziyue; Liu, Congfeng

2014-01-01

In the study of the joint estimation of time-frequency signature and direction of arrival (DOA) for multicomponent chirp signals, an estimation method based on spatial time-frequency distributions (STFDs) is proposed in this paper. Firstly, array signal model for multicomponent chirp signals is presented and then array processing is applied in time-frequency analysis to mitigate cross-terms. According to the results of the array processing, Hough transform is performed and the estimation of time-frequency signature is obtained. Subsequently, subspace method for DOA estimation based on STFD matrix is achieved. Simulation results demonstrate the validity of the proposed method.

Method for extracting long-equivalent wavelength interferometric information

NASA Technical Reports Server (NTRS)

Hochberg, Eric B. (Inventor)

1991-01-01

A process for extracting long-equivalent wavelength interferometric information from a two-wavelength polychromatic or achromatic interferometer. The process comprises the steps of simultaneously recording a non-linear sum of two different frequency visible light interferograms on a high resolution film and then placing the developed film in an optical train for Fourier transformation, low pass spatial filtering and inverse transformation of the film image to produce low spatial frequency fringes corresponding to a long-equivalent wavelength interferogram. The recorded non-linear sum irradiance derived from the two-wavelength interferometer is obtained by controlling the exposure so that the average interferogram irradiance is set at either the noise level threshold or the saturation level threshold of the film.

[Study of Image Quality Comparison Based on the MTF Method Between Different Medical Rigid Endoscopes in an In Vitro Model].

PubMed

Wang, Yunlong; Ji, Jun; Jiang, Changsong; Huang, Zengyue

2015-04-01

This study was aimed to use the method of modulation transfer function (MTF) to compare image quality among three different Olympus medical rigid cystoscopes in an in vitro model. During the experimental processes, we firstly used three different types of cystoscopes (i. e. OLYMPUS cystourethroscopy with FOV of 12 degrees, OLYMPUS Germany A22003A and OLYMPUS A2013A) to collect raster images at different brightness with industrial camera and computer from the resolution target which is with different spatial frequency, and then we processed the collected images using MALAB software with the optical transfer function MTF to obtain the values of MTF at different brightness and different spatial frequency. We then did data mathematical statistics and compared imaging quality. The statistical data showed that all three MTF values were smaller than 1. MTF values with the spatial frequency gradually increasing would decrease approaching 0 at the same brightness. When the brightness enhanced in the same process at the same spatial frequency, MTF values showed a slowly increasing trend. The three endoscopes' MTF values were completely different. In some cases the MTF values had a large difference, and the maximum difference could reach 0.7. Conclusion can be derived from analysis of experimental data that three Olympus medical rigid cystoscopes have completely different imaging quality abilities. The No. 3 endoscope OLYMPUS A2013A has low resolution but high contrast. The No. 1 endoscope OLYMPUS cystourethroscopy with FOV of 12 degrees, on the contrary, had high resolution and lower contrast. The No. 2 endoscope OLYMPUS Germany A22003A had high contrast and high resolution, and its image quality was the best.

Cross-scale analysis of fire regimes

Treesearch

Donald A. Falk; Carol Miller; Donald McKenzie; Anne E. Black

2007-01-01

Cross-scale spatial and temporal perspectives are important for studying contagious landscape disturbances such as fire, which are controlled by myriad processes operating at different scales. We examine fire regimes in forests of western North America, focusing on how observed patterns of fire frequency change across spatial scales. To quantify changes in fire...

Selective loss of orientation column maps in visual cortex during brief elevation of intraocular pressure.

PubMed

Chen, Xin; Sun, Chao; Huang, Luoxiu; Shou, Tiande

2003-01-01

To compare the orientation column maps elicited by different spatial frequency gratings in cortical area 17 of cats before and during brief elevation of intraocular pressure (IOP). IOP was elevated by injecting saline into the anterior chamber of a cat's eye through a syringe needle. The IOP was elevated enough to cause a retinal perfusion pressure (arterial pressure minus IOP) of approximately 30 mm Hg during a brief elevation of IOP. The visual stimulus gratings were varied in spatial frequency, whereas other parameters were kept constant. The orientation column maps of the cortical area 17 were monocularly elicited by drifting gratings of different spatial frequencies and revealed by a brain intrinsic signal optical imaging system. These maps were compared before and during short-term elevation of IOP. The response amplitude of the orientation maps in area 17 decreased during a brief elevation of IOP. This decrease was dependent on the retinal perfusion pressure but not on the absolute IOP. The location of the most visible maps was spatial-frequency dependent. The blurring or loss of the pattern of the orientation maps was most severe when high-spatial-frequency gratings were used and appeared most significantly on the posterior part of the exposed cortex while IOP was elevated. However, the basic patterns of the maps remained unchanged. Changes in cortical signal were not due to changes in the optics of the eye with elevation of IOP. A stable normal IOP is essential for maintaining normal visual cortical functions. During a brief and high elevation of IOP, the cortical processing of high-spatial-frequency visual information was diminished because of a selectively functional decline of the retinogeniculocortical X pathway by a mechanism of retinal circulation origin.

Contributions of Low and High Spatial Frequency Processing to Impaired Object Recognition Circuitry in Schizophrenia

PubMed Central

Calderone, Daniel J.; Hoptman, Matthew J.; Martínez, Antígona; Nair-Collins, Sangeeta; Mauro, Cristina J.; Bar, Moshe; Javitt, Daniel C.; Butler, Pamela D.

2013-01-01

Patients with schizophrenia exhibit cognitive and sensory impairment, and object recognition deficits have been linked to sensory deficits. The “frame and fill” model of object recognition posits that low spatial frequency (LSF) information rapidly reaches the prefrontal cortex (PFC) and creates a general shape of an object that feeds back to the ventral temporal cortex to assist object recognition. Visual dysfunction findings in schizophrenia suggest a preferential loss of LSF information. This study used functional magnetic resonance imaging (fMRI) and resting state functional connectivity (RSFC) to investigate the contribution of visual deficits to impaired object “framing” circuitry in schizophrenia. Participants were shown object stimuli that were intact or contained only LSF or high spatial frequency (HSF) information. For controls, fMRI revealed preferential activation to LSF information in precuneus, superior temporal, and medial and dorsolateral PFC areas, whereas patients showed a preference for HSF information or no preference. RSFC revealed a lack of connectivity between early visual areas and PFC for patients. These results demonstrate impaired processing of LSF information during object recognition in schizophrenia, with patients instead displaying increased processing of HSF information. This is consistent with findings of a preference for local over global visual information in schizophrenia. PMID:22735157

Dissociation of sensitivity to spatial frequency in word and face preferential areas of the fusiform gyrus.

PubMed

Woodhead, Zoe Victoria Joan; Wise, Richard James Surtees; Sereno, Marty; Leech, Robert

2011-10-01

Different cortical regions within the ventral occipitotemporal junction have been reported to show preferential responses to particular objects. Thus, it is argued that there is evidence for a left-lateralized visual word form area and a right-lateralized fusiform face area, but the unique specialization of these areas remains controversial. Words are characterized by greater power in the high spatial frequency (SF) range, whereas faces comprise a broader range of high and low frequencies. We investigated how these high-order visual association areas respond to simple sine-wave gratings that varied in SF. Using functional magnetic resonance imaging, we demonstrated lateralization of activity that was concordant with the low-level visual property of words and faces; left occipitotemporal cortex is more strongly activated by high than by low SF gratings, whereas the right occipitotemporal cortex responded more to low than high spatial frequencies. Therefore, the SF of a visual stimulus may bias the lateralization of processing irrespective of its higher order properties.

Interaction of an electromagnetic wave with a rapidly created spatially periodic plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuo, S.P.; Faith, J.

1997-08-01

The interaction of electromagnetic waves with rapidly created time-varying spatially periodic plasmas is studied. The numerical results of the collisionless case show that both frequency upshifted and frequency downshifted waves are generated. Moreover, the frequency downshifted waves are trapped by the plasma when the plasma frequency is larger than the wave frequency. The trapping has the effect of dramatically enhancing the efficiency of the frequency downshift conversion process, by accumulating incident wave energy during the plasma transition period. A theory based on the wave impedance of each Floquet mode of the periodic structure is formulated, incorporating with the collisional dampingmore » of the plasma. Such a theory explains the recent experimental observations [Faith, Kuo, and Huang, Phys. Rev. E {bold 55}, 1843 (1997)] where the frequency downshifted signals were detected repetitively with considerably enhanced spectral intensities while the frequency upshifted signals were missing. {copyright} {ital 1997} {ital The American Physical Society}« less

Combining Temporal and Spectral Information with Spatial Mapping to Identify Differences between Phonological and Semantic Networks: A Magnetoencephalographic Approach

PubMed Central

McNab, Fiona; Hillebrand, Arjan; Swithenby, Stephen J.; Rippon, Gina

2012-01-01

Early, lesion-based models of language processing suggested that semantic and phonological processes are associated with distinct temporal and parietal regions respectively, with frontal areas more indirectly involved. Contemporary spatial brain mapping techniques have not supported such clear-cut segregation, with strong evidence of activation in left temporal areas by both processes and disputed evidence of involvement of frontal areas in both processes. We suggest that combining spatial information with temporal and spectral data may allow a closer scrutiny of the differential involvement of closely overlapping cortical areas in language processing. Using beamforming techniques to analyze magnetoencephalography data, we localized the neuronal substrates underlying primed responses to nouns requiring either phonological or semantic processing, and examined the associated measures of time and frequency in those areas where activation was common to both tasks. Power changes in the beta (14–30 Hz) and gamma (30–50 Hz) frequency bands were analyzed in pre-selected time windows of 350–550 and 500–700 ms In left temporal regions, both tasks elicited power changes in the same time window (350–550 ms), but with different spectral characteristics, low beta (14–20 Hz) for the phonological task and high beta (20–30 Hz) for the semantic task. In frontal areas (BA10), both tasks elicited power changes in the gamma band (30–50 Hz), but in different time windows, 500–700 ms for the phonological task and 350–550 ms for the semantic task. In the left inferior parietal area (BA40), both tasks elicited changes in the 20–30 Hz beta frequency band but in different time windows, 350–550 ms for the phonological task and 500–700 ms for the semantic task. Our findings suggest that, where spatial measures may indicate overlapping areas of involvement, additional beamforming techniques can demonstrate differential activation in time and frequency domains. PMID:22908001

Exogenous attention enhances 2nd-order contrast sensitivity

PubMed Central

Barbot, Antoine; Landy, Michael S.; Carrasco, Marisa

2011-01-01

Natural scenes contain a rich variety of contours that the visual system extracts to segregrate the retinal image into perceptually coherent regions. Covert spatial attention helps extract contours by enhancing contrast sensitivity for 1st-order, luminance-defined patterns at attended locations, while reducing sensitivity at unattended locations, relative to neutral attention allocation. However, humans are also sensitive to 2nd-order patterns such as spatial variations of texture, which are predominant in natural scenes and cannot be detected by linear mechanisms. We assess whether and how exogenous attention—the involuntary and transient capture of spatial attention—affects the contrast sensitivity of channels sensitive to 2nd-order, texture-defined patterns. Using 2nd-order, texture-defined stimuli, we demonstrate that exogenous attention increases 2nd-order contrast sensitivity at the attended location, while decreasing it at unattended locations, relative to a neutral condition. By manipulating both 1st- and 2nd-order spatial frequency, we find that the effects of attention depend both on 2nd-order spatial frequency of the stimulus and the observer’s 2nd-order spatial resolution at the target location. At parafoveal locations, attention enhances 2nd-order contrast sensitivity to high, but not to low 2nd-order spatial frequencies; at peripheral locations attention also enhances sensitivity to low 2nd-order spatial frequencies. Control experiments rule out the possibility that these effects might be due to an increase in contrast sensitivity at the 1st-order stage of visual processing. Thus, exogenous attention affects 2nd-order contrast sensitivity at both attended and unattended locations. PMID:21356228

Die Fledermaus: Regarding Optokinetic Contrast Sensitivity and Light-Adaptation, Chicks Are Mice with Wings

PubMed Central

Shi, Qing; Stell, William K.

2013-01-01

Background Through adaptation, animals can function visually under an extremely broad range of light intensities. Light adaptation starts in the retina, through shifts in photoreceptor sensitivity and kinetics plus modulation of visual processing in retinal circuits. Although considerable research has been conducted on retinal adaptation in nocturnal species with rod-dominated retinas, such as the mouse, little is known about how cone-dominated avian retinas adapt to changes in mean light intensity. Methodology/Principal Findings We used the optokinetic response to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. We found that: 1) daytime, cone-driven CS was tuned to spatial frequency; 2) nighttime, presumably rod-driven CS was tuned to temporal frequency and spatial frequency; 3) daytime, presumably cone-driven CS at threshold intensity was invariant with temporal and spatial frequency; and 4) daytime photopic CS was invariant with clock time. Conclusion/Significance Light- and dark-adaptational changes in CS were investigated comprehensively for the first time in the cone-dominated retina of an avian, diurnal species. The chick retina, like the mouse retina, adapts by using a “day/night” or “cone/rod” switch in tuning preference during changes in lighting conditions. The chick optokinetic response is an attractive model for noninvasive, behavioral studies of adaptation in retinal circuitry in health and disease. PMID:24098693

Modalities of Thinking: State and Trait Effects on Cross-Frequency Functional Independent Brain Networks.

PubMed

Milz, Patricia; Pascual-Marqui, Roberto D; Lehmann, Dietrich; Faber, Pascal L

2016-05-01

Functional states of the brain are constituted by the temporally attuned activity of spatially distributed neural networks. Such networks can be identified by independent component analysis (ICA) applied to frequency-dependent source-localized EEG data. This methodology allows the identification of networks at high temporal resolution in frequency bands of established location-specific physiological functions. EEG measurements are sensitive to neural activity changes in cortical areas of modality-specific processing. We tested effects of modality-specific processing on functional brain networks. Phasic modality-specific processing was induced via tasks (state effects) and tonic processing was assessed via modality-specific person parameters (trait effects). Modality-specific person parameters and 64-channel EEG were obtained from 70 male, right-handed students. Person parameters were obtained using cognitive style questionnaires, cognitive tests, and thinking modality self-reports. EEG was recorded during four conditions: spatial visualization, object visualization, verbalization, and resting. Twelve cross-frequency networks were extracted from source-localized EEG across six frequency bands using ICA. RMANOVAs, Pearson correlations, and path modelling examined effects of tasks and person parameters on networks. Results identified distinct state- and trait-dependent functional networks. State-dependent networks were characterized by decreased, trait-dependent networks by increased alpha activity in sub-regions of modality-specific pathways. Pathways of competing modalities showed opposing alpha changes. State- and trait-dependent alpha were associated with inhibitory and automated processing, respectively. Antagonistic alpha modulations in areas of competing modalities likely prevent intruding effects of modality-irrelevant processing. Considerable research suggested alpha modulations related to modality-specific states and traits. This study identified the distinct electrophysiological cortical frequency-dependent networks within which they operate.

Joint Entropy for Space and Spatial Frequency Domains Estimated from Psychometric Functions of Achromatic Discrimination

PubMed Central

Silveira, Vladímir de Aquino; Souza, Givago da Silva; Gomes, Bruno Duarte; Rodrigues, Anderson Raiol; Silveira, Luiz Carlos de Lima

2014-01-01

We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4π or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint entropy for these stimulus conditions when contrast was raised. PMID:24466158

Joint entropy for space and spatial frequency domains estimated from psychometric functions of achromatic discrimination.

PubMed

Silveira, Vladímir de Aquino; Souza, Givago da Silva; Gomes, Bruno Duarte; Rodrigues, Anderson Raiol; Silveira, Luiz Carlos de Lima

2014-01-01

We used psychometric functions to estimate the joint entropy for space discrimination and spatial frequency discrimination. Space discrimination was taken as discrimination of spatial extent. Seven subjects were tested. Gábor functions comprising unidimensionalsinusoidal gratings (0.4, 2, and 10 cpd) and bidimensionalGaussian envelopes (1°) were used as reference stimuli. The experiment comprised the comparison between reference and test stimulithat differed in grating's spatial frequency or envelope's standard deviation. We tested 21 different envelope's standard deviations around the reference standard deviation to study spatial extent discrimination and 19 different grating's spatial frequencies around the reference spatial frequency to study spatial frequency discrimination. Two series of psychometric functions were obtained for 2%, 5%, 10%, and 100% stimulus contrast. The psychometric function data points for spatial extent discrimination or spatial frequency discrimination were fitted with Gaussian functions using the least square method, and the spatial extent and spatial frequency entropies were estimated from the standard deviation of these Gaussian functions. Then, joint entropy was obtained by multiplying the square root of space extent entropy times the spatial frequency entropy. We compared our results to the theoretical minimum for unidimensional Gábor functions, 1/4π or 0.0796. At low and intermediate spatial frequencies and high contrasts, joint entropy reached levels below the theoretical minimum, suggesting non-linear interactions between two or more visual mechanisms. We concluded that non-linear interactions of visual pathways, such as the M and P pathways, could explain joint entropy values below the theoretical minimum at low and intermediate spatial frequencies and high contrasts. These non-linear interactions might be at work at intermediate and high contrasts at all spatial frequencies once there was a substantial decrease in joint entropy for these stimulus conditions when contrast was raised.

Symmetry-protected zero-mode laser with a tunable spatial profile

NASA Astrophysics Data System (ADS)

Ge, Li

Majorana zero modes in condense matter systems have attracted considerable interest in topological quantum computation. In contrast, while robust zero modes have been observed in various photonic lattices, it remains an open question whether they can be used for the same purpose. To advance significantly the state-of-the-art in zero-mode photonics, new inspirations are needed for a better design and control of photonic systems. Using the zero modes protected by non-Hermitian particle-hole symmetry in a photonic lattice and the spatial degrees of freedom they offer, we propose a single-mode, fixed-frequency, and spatially tunable zero-mode laser. The system does not need to have zero modes before a localized pump is applied; they are created by the spontaneous restoration of particle-hole symmetry. By modifying this process using different pump configurations, we present a versatile way to tune the spatial profile of our zero-mode laser, with its lasing frequency pinned at the zero energy. Such a zero-mode laser may find applications in telecommunication, where spatial encoding is held by some to be last frontier of signal processing. This project is supported by the NSF under Grant No. DMR-1506987.

Soliton triads ensemble in frequency conversion: from inverse scattering theory to experimental observation.

PubMed

Baronio, Fabio; Andreana, Marco; Conforti, Matteo; Manili, Gabriele; Couderc, Vincent; De Angelis, Costantino; Barthélémy, Alain

2011-07-04

We consider the spectral theory of three-wave interactions to predict the initiation, formation and dynamics of an ensemble of bright-dark-bright soliton triads in frequency conversion processes. Spatial observation of non-interacting triads ensemble in a KTP crystal confirms theoretical prediction and numerical simulations.

Analysis of PVA/AA based photopolymers at the zero spatial frequency limit using interferometric methods.

PubMed

Gallego, Sergi; Márquez, Andrés; Méndez, David; Ortuño, Manuel; Neipp, Cristian; Fernández, Elena; Pascual, Inmaculada; Beléndez, Augusto

2008-05-10

One of the problems associated with photopolymers as optical recording media is the thickness variation during the recording process. Different values of shrinkages or swelling are reported in the literature for photopolymers. Furthermore, these variations depend on the spatial frequencies of the gratings stored in the materials. Thickness variations can be measured using different methods: studying the deviation from the Bragg's angle for nonslanted gratings, using MicroXAM S/N 8038 interferometer, or by the thermomechanical analysis experiments. In a previous paper, we began the characterization of the properties of a polyvinyl alcohol/acrylamide based photopolymer at the lowest end of recorded spatial frequencies. In this work, we continue analyzing the thickness variations of these materials using a reflection interferometer. With this technique we are able to obtain the variations of the layers refractive index and, therefore, a direct estimation of the polymer refractive index.

Paradoxical Cross-Over Due to Attention to High or Low Spatial Frequencies

ERIC Educational Resources Information Center

Niemeier, Matthias; Stojanoski, Boge; Singh, Vaughan W. A.; Chu, Eddie

2008-01-01

The mechanisms underlying the right hemisphere's dominance for spatial and attentional functions lacks a comprehensively explanation. For example, perceptual biases, as observed in line bisection and related tasks, might be caused by an attentional asymmetry or by perceptual processes such as a specialization of the left and right hemisphere for…

(abstract) Topographic Signatures in Geology

NASA Technical Reports Server (NTRS)

Farr, Tom G.; Evans, Diane L.

1996-01-01

Topographic information is required for many Earth Science investigations. For example, topography is an important element in regional and global geomorphic studies because it reflects the interplay between the climate-driven processes of erosion and the tectonic processes of uplift. A number of techniques have been developed to analyze digital topographic data, including Fourier texture analysis. A Fourier transform of the topography of an area allows the spatial frequency content of the topography to be analyzed. Band-pass filtering of the transform produces images representing the amplitude of different spatial wavelengths. These are then used in a multi-band classification to map units based on their spatial frequency content. The results using a radar image instead of digital topography showed good correspondence to a geologic map, however brightness variations in the image unrelated to topography caused errors. An additional benefit to the use of Fourier band-pass images for the classification is that the textural signatures of the units are quantative measures of the spatial characteristics of the units that may be used to map similar units in similar environments.

Spatial Resolution Characterization for QuickBird Image Products 2003-2004 Season

NASA Technical Reports Server (NTRS)

Blonski, Slawomir

2006-01-01

This presentation focuses on spatial resolution characterization for QuickBird panochromatic images in 2003-2004 and presents data measurements and analysis of SSC edge target deployment and edge response extraction and modeling. The results of the characterization are shown as values of the Modulation Transfer Function (MTF) at the Nyquist spatial frequency and as the Relative Edge Response (RER) components. The results show that RER is much less sensitive to accuracy of the curve fitting than the value of MTF at Nyquist frequency. Therefore, the RER/edge response slope is a more robust estimator of the digital image spatial resolution than the MTF. For the QuickBird panochromatic images, the RER is consistently equal to 0.5 for images processed with the Cubic Convolution resampling and to 0.8 for the MTF resampling.

Beyond time and space: The effect of a lateralized sustained attention task and brain stimulation on spatial and selective attention.

PubMed

Shalev, Nir; De Wandel, Linde; Dockree, Paul; Demeyere, Nele; Chechlacz, Magdalena

2017-10-03

The Theory of Visual Attention (TVA) provides a mathematical formalisation of the "biased competition" account of visual attention. Applying this model to individual performance in a free recall task allows the estimation of 5 independent attentional parameters: visual short-term memory (VSTM) capacity, speed of information processing, perceptual threshold of visual detection; attentional weights representing spatial distribution of attention (spatial bias), and the top-down selectivity index. While the TVA focuses on selection in space, complementary accounts of attention describe how attention is maintained over time, and how temporal processes interact with selection. A growing body of evidence indicates that different facets of attention interact and share common neural substrates. The aim of the current study was to modulate a spatial attentional bias via transfer effects, based on a mechanistic understanding of the interplay between spatial, selective and temporal aspects of attention. Specifically, we examined here: (i) whether a single administration of a lateralized sustained attention task could prime spatial orienting and lead to transferable changes in attentional weights (assigned to the left vs right hemi-field) and/or other attentional parameters assessed within the framework of TVA (Experiment 1); (ii) whether the effects of such spatial-priming on TVA parameters could be further enhanced by bi-parietal high frequency transcranial random noise stimulation (tRNS) (Experiment 2). Our results demonstrate that spatial attentional bias, as assessed within the TVA framework, was primed by sustaining attention towards the right hemi-field, but this spatial-priming effect did not occur when sustaining attention towards the left. Furthermore, we show that bi-parietal high-frequency tRNS combined with the rightward spatial-priming resulted in an increased attentional selectivity. To conclude, we present a novel, theory-driven method for attentional modulation providing important insights into how the spatial and temporal processes in attention interact with attentional selection. Copyright © 2017 Elsevier Ltd. All rights reserved.

Limitations of contrast enhancement for infrared target identification

NASA Astrophysics Data System (ADS)

Du Bosq, Todd W.; Fanning, Jonathan D.

2009-05-01

Contrast enhancement and dynamic range compression are currently being used to improve the performance of infrared imagers by increasing the contrast between the target and the scene content. Automatic contrast enhancement techniques do not always achieve this improvement. In some cases, the contrast can increase to a level of target saturation. This paper assesses the range-performance effects of contrast enhancement for target identification as a function of image saturation. Human perception experiments were performed to determine field performance using contrast enhancement on the U.S. Army RDECOM CERDEC NVESD standard military eight target set using an un-cooled LWIR camera. The experiments compare the identification performance of observers viewing contrast enhancement processed images at various levels of saturation. Contrast enhancement is modeled in the U.S. Army thermal target acquisition model (NVThermIP) by changing the scene contrast temperature. The model predicts improved performance based on any improved target contrast, regardless of specific feature saturation or enhancement. The measured results follow the predicted performance based on the target task difficulty metric used in NVThermIP for the non-saturated cases. The saturated images reduce the information contained in the target and performance suffers. The model treats the contrast of the target as uniform over spatial frequency. As the contrast is enhanced, the model assumes that the contrast is enhanced uniformly over the spatial frequencies. After saturation, the spatial cues that differentiate one tank from another are located in a limited band of spatial frequencies. A frequency dependent treatment of target contrast is needed to predict performance of over-processed images.

Simultaneous storage of medical images in the spatial and frequency domain: a comparative study.

PubMed

Nayak, Jagadish; Bhat, P Subbanna; Acharya U, Rajendra; Uc, Niranjan

2004-06-05

Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. The patient information is encrypted before interleaving with images to ensure greater security. The bio-signals are compressed and subsequently interleaved with the image. This interleaving is carried out in the spatial domain and Frequency domain. The performance of interleaving in the spatial, Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) coefficients is studied. Differential pulse code modulation (DPCM) is employed for data compression as well as encryption and results are tabulated for a specific example. It can be seen from results, the process does not affect the picture quality. This is attributed to the fact that the change in LSB of a pixel changes its brightness by 1 part in 256. Spatial and DFT domain interleaving gave very less %NRMSE as compared to DCT and DWT domain. The Results show that spatial domain the interleaving, the %NRMSE was less than 0.25% for 8-bit encoded pixel intensity. Among the frequency domain interleaving methods, DFT was found to be very efficient.

An Observation-based Assessment of Instrument Requirements for a Future Precipitation Process Observing System

NASA Astrophysics Data System (ADS)

Nelson, E.; L'Ecuyer, T. S.; Wood, N.; Smalley, M.; Kulie, M.; Hahn, W.

2017-12-01

Global models exhibit substantial biases in the frequency, intensity, duration, and spatial scales of precipitation systems. Much of this uncertainty stems from an inadequate representation of the processes by which water is cycled between the surface and atmosphere and, in particular, those that govern the formation and maintenance of cloud systems and their propensity to form the precipitation. Progress toward improving precipitation process models requires observing systems capable of quantifying the coupling between the ice content, vertical mass fluxes, and precipitation yield of precipitating cloud systems. Spaceborne multi-frequency, Doppler radar offers a unique opportunity to address this need but the effectiveness of such a mission is heavily dependent on its ability to actually observe the processes of interest in the widest possible range of systems. Planning for a next generation precipitation process observing system should, therefore, start with a fundamental evaluation of the trade-offs between sensitivity, resolution, sampling, cost, and the overall potential scientific yield of the mission. Here we provide an initial assessment of the scientific and economic trade-space by evaluating hypothetical spaceborne multi-frequency radars using a combination of current real-world and model-derived synthetic observations. Specifically, we alter the field of view, vertical resolution, and sensitivity of a hypothetical Ka- and W-band radar system and propagate those changes through precipitation detection and intensity retrievals. The results suggest that sampling biases introduced by reducing sensitivity disproportionately affect the light rainfall and frozen precipitation regimes that are critical for warm cloud feedbacks and ice sheet mass balance, respectively. Coarser spatial resolution observations introduce regime-dependent biases in both precipitation occurrence and intensity that depend on cloud regime, with even the sign of the bias varying within a single storm system. It is suggested that the next generation spaceborne radar have a minimum sensitivity of -5 dBZ and spatial resolution of at least 3 km at all frequencies to adequately sample liquid and ice phase precipitation processes globally.

A Spatial and Temporal Frequency Based Figure-Ground Processor

NASA Astrophysics Data System (ADS)

Weisstein, Namoi; Wong, Eva

1990-03-01

Recent findings in visual psychophysics have shown that figure-ground perception can be specified by the spatial and temporal response characteristics of the visual system. Higher spatial frequency regions of the visual field are perceived as figure and lower spatial frequency regions are perceived as background/ (Klymenko and Weisstein, 1986, Wong and Weisstein, 1989). Higher temporal frequency regions are seen as background and lower temporal frequency regions are seen as figure (Wong and Weisstein, 1987, Klymenko, Weisstein, Topolski, and Hsieh, 1988). Thus, high spatial and low temporal frequencies appear to be associated with figure and low spatial and high temporal frequencies appear to be associated with background.

Spatiotemporal analysis of brightness induction

PubMed Central

McCourt, Mark E.

2011-01-01

Brightness induction refers to a class of visual illusions in which the perceived intensity of a region of space is influenced by the luminance of surrounding regions. These illusions are significant because they provide insight into the neural organization of the visual system. A novel quadrature-phase motion cancelation technique was developed to measure the magnitude of the grating induction brightness illusion across a wide range of spatial frequencies, temporal frequencies and test field heights. Canceling contrast is greatest at low frequencies and declines with increasing frequency in both dimensions, and with increasing test field height. Canceling contrast scales as the product of inducing grating spatial frequency and test field height (the number of inducing grating cycles per test field height). When plotted using a spatial axis which indexes this product, the spatiotemporal induction surfaces for four test field heights can be described as four partially overlapping sections of a single larger surface. These properties of brightness induction are explained in the context of multiscale spatial filtering. The present study is the first to measure the magnitude of grating induction as a function of temporal frequency. Taken in conjunction with several other studies (Blakeslee & McCourt, 2008; Robinson & de Sa, 2008; Magnussen & Glad, 1975) the results of this study illustrate that at least one form of brightness induction is very much faster than that reported by DeValois et al. (1986) and Rossi and Paradiso (1996), and are inconsistent with the proposition that brightness induction results from a slow “filling in” process. PMID:21763339

Input-dependent frequency modulation of cortical gamma oscillations shapes spatial synchronization and enables phase coding.

PubMed

Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter

2015-02-01

Fine-scale temporal organization of cortical activity in the gamma range (∼25-80Hz) may play a significant role in information processing, for example by neural grouping ('binding') and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency codes or slower oscillation phase codes, may resolve conflicting experimental observations on gamma phase coding. Our modeling results offer clear testable experimental predictions. We conclude that input-dependency of gamma frequencies could be essential rather than detrimental for meaningful gamma-mediated temporal organization of cortical activity.

Input-Dependent Frequency Modulation of Cortical Gamma Oscillations Shapes Spatial Synchronization and Enables Phase Coding

PubMed Central

Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter

2015-01-01

Fine-scale temporal organization of cortical activity in the gamma range (∼25–80Hz) may play a significant role in information processing, for example by neural grouping (‘binding’) and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency codes or slower oscillation phase codes, may resolve conflicting experimental observations on gamma phase coding. Our modeling results offer clear testable experimental predictions. We conclude that input-dependency of gamma frequencies could be essential rather than detrimental for meaningful gamma-mediated temporal organization of cortical activity. PMID:25679780

Importance of phase alignment for interocular suppression.

PubMed

Maehara, Goro; Huang, Pi-Chun; Hess, Robert F

2009-07-01

We measured contrast thresholds for Gabor targets in the presence of maskers which had higher or lower spatial frequencies than the targets. A high-pass fractal masker elevated target contrast thresholds at low and intermediate pedestal contrasts in both monocular and dichoptic modes of presentation, suggesting that the masking occurs after a monocular processing stage. Moreover we found that a high-pass checkerboard masker elevated thresholds at the low and intermediate pedestal contrasts and that most of this threshold elevation disappeared when the phase of the masker's spatial components were scrambled. This masking was effective only in the dichoptic presentation, not in the monocular presentation. These results indicate that phase alignment of the high spatial frequency components plays a crucial role for interocular suppression. We speculate that phase alignments signal the existence of a luminance contour in the monocular image and that this signal suppresses processing of information in the other eye when there is no corresponding signal in that eye.

Review of image processing fundamentals

NASA Technical Reports Server (NTRS)

Billingsley, F. C.

1985-01-01

Image processing through convolution, transform coding, spatial frequency alterations, sampling, and interpolation are considered. It is postulated that convolution in one domain (real or frequency) is equivalent to multiplication in the other (frequency or real), and that the relative amplitudes of the Fourier components must be retained to reproduce any waveshape. It is suggested that all digital systems may be considered equivalent, with a frequency content approximately at the Nyquist limit, and with a Gaussian frequency response. An optimized cubic version of the interpolation continuum image is derived as a set of cubic spines. Pixel replication has been employed to enlarge the visable area of digital samples, however, suitable elimination of the extraneous high frequencies involved in the visable edges, by defocusing, is necessary to allow the underlying object represented by the data values to be seen.

Infrared and visual image fusion method based on discrete cosine transform and local spatial frequency in discrete stationary wavelet transform domain

NASA Astrophysics Data System (ADS)

Jin, Xin; Jiang, Qian; Yao, Shaowen; Zhou, Dongming; Nie, Rencan; Lee, Shin-Jye; He, Kangjian

2018-01-01

In order to promote the performance of infrared and visual image fusion and provide better visual effects, this paper proposes a hybrid fusion method for infrared and visual image by the combination of discrete stationary wavelet transform (DSWT), discrete cosine transform (DCT) and local spatial frequency (LSF). The proposed method has three key processing steps. Firstly, DSWT is employed to decompose the important features of the source image into a series of sub-images with different levels and spatial frequencies. Secondly, DCT is used to separate the significant details of the sub-images according to the energy of different frequencies. Thirdly, LSF is applied to enhance the regional features of DCT coefficients, and it can be helpful and useful for image feature extraction. Some frequently-used image fusion methods and evaluation metrics are employed to evaluate the validity of the proposed method. The experiments indicate that the proposed method can achieve good fusion effect, and it is more efficient than other conventional image fusion methods.

System for generating pluralities of optical pulses with predetermined frequencies in a temporally and spatially overlapped relationship

DOEpatents

Meyerhofer, David D.; Schmid, Ansgar W.; Chuang, Yung-ho

1992-01-01

Ultra short (pico second and shorter) laser pulses having components of different frequency which are overlapped coherently in space and with a predetermined constant relationship in time, are generated and may be used in applications where plural spectrally separate, time-synchronized pulses are needed as in wave-length resolved spectroscopy and spectral pump probe measurements for characterization of materials. A Chirped Pulse Amplifier (CPA), such as a regenerative amplifier, which provides amplified, high intensity pulses at the output thereof which have the same spatial intensity profile, is used to process a series of chirped pulses, each with a different central frequency (the desired frequencies contained in the output pulses). Each series of chirped pulses is obtained from a single chirped pulse by spectral windowing with a mask in a dispersive expansion stage ahead of the laser amplifier. The laser amplifier amplifies the pulses and provides output pulses with like spatial and temporal profiles. A compression stage then compresses the amplified pulses. All the individual pulses of different frequency, which originated in each single chirped pulse, are compressed and thereby coherently overlapped in space and time. The compressed pulses may be used for the foregoing purposes and other purposes wherien pulses having a plurality of discrete frequency components are required.

System for generating pluralities of optical pulses with predetermined frequencies in a temporally and spatially overlapped relationship

DOEpatents

Meyerhofer, D.D.; Schmid, A.W.; Chuang, Y.

1992-03-10

Ultrashort (pico second and shorter) laser pulses having components of different frequency which are overlapped coherently in space and with a predetermined constant relationship in time, are generated and may be used in applications where plural spectrally separate, time-synchronized pulses are needed as in wave-length resolved spectroscopy and spectral pump probe measurements for characterization of materials. A Chirped Pulse Amplifier (CPA), such as a regenerative amplifier, which provides amplified, high intensity pulses at the output thereof which have the same spatial intensity profile, is used to process a series of chirped pulses, each with a different central frequency (the desired frequencies contained in the output pulses). Each series of chirped pulses is obtained from a single chirped pulse by spectral windowing with a mask in a dispersive expansion stage ahead of the laser amplifier. The laser amplifier amplifies the pulses and provides output pulses with like spatial and temporal profiles. A compression stage then compresses the amplified pulses. All the individual pulses of different frequency, which originated in each single chirped pulse, are compressed and thereby coherently overlapped in space and time. The compressed pulses may be used for the foregoing purposes and other purposes wherien pulses having a plurality of discrete frequency components are required. 4 figs.

Coherent dual-frequency lidar system design for distance and speed measurements

NASA Astrophysics Data System (ADS)

Zheng, Xingyuan; Zhao, Changming; Zhang, Haiyang; Zheng, Zheng; Yang, Hongzhi

2018-01-01

Lidars have a wide range of applications in military detection and civilian remote sensing. Coherent Dual-Frequency Lidar (CDFL) is a new concept of laser radar that is using electrical coherence instead of optical coherence. It uses laser with two coherent frequency components as transmitting wave. The method is based on the use of an optically-carried radio frequency (RF) signal, which is the frequency difference between the two components, which is specially designed for distance and speed measurements. It not only ensures the system has the characteristics of high spatial resolution, high ranging and velocity precision of laser radar, but also can use mature signal processing technology of microwave radar, and it is a research direction that attracts more concern in recent years. A CDFL detection system is constructed and field experiment is carried out. In the system, a narrow linewidth fiber laser with a wavelength of 1064nm is adopted. The dual-frequency laser with frequency difference of 200MHz and 200.6MHz is obtained by acousto-optic frequency shift and recombination. The maximum output power of dual frequency laser is 200mW. The receiver consists of all-fiber balanced InGaAs photo-detector and homemade analog signal processing board. The experimental results show that the distance resolution and velocity resolution of the system are 0.1m and 0.1m/s separately when the working distance is greater than 200m, and the spatial resolution is 0.5mrad.

Eliminating spiral waves pinned to an anatomical obstacle in cardiac myocytes by high-frequency stimuli.

PubMed

Isomura, Akihiro; Hörning, Marcel; Agladze, Konstantin; Yoshikawa, Kenichi

2008-12-01

The unpinning of spiral waves by the application of high-frequency wave trains was studied in cultured cardiac myocytes. Successful unpinning was observed when the frequency of the paced waves exceeded a critical level. The unpinning process was analyzed by a numerical simulation with a model of cardiac tissue. The mechanism of unpinning by high-frequency stimuli is discussed in terms of local entrainment failure, through a reduction of the two-dimensional spatial characteristics into one dimension.

Comparison of different spatial transformations applied to EEG data: A case study of error processing.

PubMed

Cohen, Michael X

2015-09-01

The purpose of this paper is to compare the effects of different spatial transformations applied to the same scalp-recorded EEG data. The spatial transformations applied are two referencing schemes (average and linked earlobes), the surface Laplacian, and beamforming (a distributed source localization procedure). EEG data were collected during a speeded reaction time task that provided a comparison of activity between error vs. correct responses. Analyses focused on time-frequency power, frequency band-specific inter-electrode connectivity, and within-subject cross-trial correlations between EEG activity and reaction time. Time-frequency power analyses showed similar patterns of midfrontal delta-theta power for errors compared to correct responses across all spatial transformations. Beamforming additionally revealed error-related anterior and lateral prefrontal beta-band activity. Within-subject brain-behavior correlations showed similar patterns of results across the spatial transformations, with the correlations being the weakest after beamforming. The most striking difference among the spatial transformations was seen in connectivity analyses: linked earlobe reference produced weak inter-site connectivity that was attributable to volume conduction (zero phase lag), while the average reference and Laplacian produced more interpretable connectivity results. Beamforming did not reveal any significant condition modulations of connectivity. Overall, these analyses show that some findings are robust to spatial transformations, while other findings, particularly those involving cross-trial analyses or connectivity, are more sensitive and may depend on the use of appropriate spatial transformations. Copyright © 2014 Elsevier B.V. All rights reserved.

SPECIAL ISSUE ON OPTICAL PROCESSING OF INFORMATION: Realisation of video-frequency filters on the basis of a new mode of operation of an acousto-optical correlator with spatial integration

NASA Astrophysics Data System (ADS)

Ushakov, V. N.

1995-10-01

A video-frequency acousto-optical correlator with spatial integration, which widens the functional capabilities of correlation-type acousto-optical processors, is described. The correlator is based on a two-dimensional reference transparency and it can filter arbitrary video signals of spectral width limited by the pass band of an acousto-optical modulator. The calculated pulse characteristic is governed by the structure of the reference transparency. A procedure for the synthesis of this transparency is considered and experimental results are reported.

Cholinergic enhancement of visual attention and neural oscillations in the human brain.

PubMed

Bauer, Markus; Kluge, Christian; Bach, Dominik; Bradbury, David; Heinze, Hans Jochen; Dolan, Raymond J; Driver, Jon

2012-03-06

Cognitive processes such as visual perception and selective attention induce specific patterns of brain oscillations. The neurochemical bases of these spectral changes in neural activity are largely unknown, but neuromodulators are thought to regulate processing. The cholinergic system is linked to attentional function in vivo, whereas separate in vitro studies show that cholinergic agonists induce high-frequency oscillations in slice preparations. This has led to theoretical proposals that cholinergic enhancement of visual attention might operate via gamma oscillations in visual cortex, although low-frequency alpha/beta modulation may also play a key role. Here we used MEG to record cortical oscillations in the context of administration of a cholinergic agonist (physostigmine) during a spatial visual attention task in humans. This cholinergic agonist enhanced spatial attention effects on low-frequency alpha/beta oscillations in visual cortex, an effect correlating with a drug-induced speeding of performance. By contrast, the cholinergic agonist did not alter high-frequency gamma oscillations in visual cortex. Thus, our findings show that cholinergic neuromodulation enhances attentional selection via an impact on oscillatory synchrony in visual cortex, for low rather than high frequencies. We discuss this dissociation between high- and low-frequency oscillations in relation to proposals that lower-frequency oscillations are generated by feedback pathways within visual cortex. Copyright © 2012 Elsevier Ltd. All rights reserved.

Wide-field motion tuning in nocturnal hawkmoths

PubMed Central

Theobald, Jamie C.; Warrant, Eric J.; O'Carroll, David C.

2010-01-01

Nocturnal hawkmoths are known for impressive visually guided behaviours in dim light, such as hovering while feeding from nectar-bearing flowers. This requires tight visual feedback to estimate and counter relative motion. Discrimination of low velocities, as required for stable hovering flight, is fundamentally limited by spatial resolution, yet in the evolution of eyes for nocturnal vision, maintenance of high spatial acuity compromises absolute sensitivity. To investigate these trade-offs, we compared responses of wide-field motion-sensitive neurons in three species of hawkmoth: Manduca sexta (a crepuscular hoverer), Deilephila elpenor (a fully nocturnal hoverer) and Acherontia atropos (a fully nocturnal hawkmoth that does not hover as it feeds uniquely from honey in bees' nests). We show that despite smaller eyes, the motion pathway of D. elpenor is tuned to higher spatial frequencies and lower temporal frequencies than A. atropos, consistent with D. elpenor's need to detect low velocities for hovering. Acherontia atropos, however, presumably evolved low-light sensitivity without sacrificing temporal acuity. Manduca sexta, active at higher light levels, is tuned to the highest spatial frequencies of the three and temporal frequencies comparable with A. atropos. This yields similar tuning to low velocities as in D. elpenor, but with the advantage of shorter neural delays in processing motion. PMID:19906663

Impaired recognition of facial emotions from low-spatial frequencies in Asperger syndrome.

PubMed

Kätsyri, Jari; Saalasti, Satu; Tiippana, Kaisa; von Wendt, Lennart; Sams, Mikko

2008-01-01

The theory of 'weak central coherence' [Happe, F., & Frith, U. (2006). The weak coherence account: Detail-focused cognitive style in autism spectrum disorders. Journal of Autism and Developmental Disorders, 36(1), 5-25] implies that persons with autism spectrum disorders (ASDs) have a perceptual bias for local but not for global stimulus features. The recognition of emotional facial expressions representing various different levels of detail has not been studied previously in ASDs. We analyzed the recognition of four basic emotional facial expressions (anger, disgust, fear and happiness) from low-spatial frequencies (overall global shapes without local features) in adults with an ASD. A group of 20 participants with Asperger syndrome (AS) was compared to a group of non-autistic age- and sex-matched controls. Emotion recognition was tested from static and dynamic facial expressions whose spatial frequency contents had been manipulated by low-pass filtering at two levels. The two groups recognized emotions similarly from non-filtered faces and from dynamic vs. static facial expressions. In contrast, the participants with AS were less accurate than controls in recognizing facial emotions from very low-spatial frequencies. The results suggest intact recognition of basic facial emotions and dynamic facial information, but impaired visual processing of global features in ASDs.

Distortions in recall from visual memory: two classes of attractors at work.

PubMed

Huang, Jie; Sekuler, Robert

2010-02-24

In a trio of experiments, a matching procedure generated direct, analogue measures of short-term memory for the spatial frequency of Gabor stimuli. Experiment 1 showed that when just a single Gabor was presented for study, a retention interval of just a few seconds was enough to increase the variability of matches, suggesting that noise in memory substantially exceeds that in vision. Experiment 2 revealed that when a pair of Gabors was presented on each trial, the remembered appearance of one of the Gabors was influenced by: (1) the relationship between its spatial frequency and the spatial frequency of the accompanying, task-irrelevant non-target stimulus; and (2) the average spatial frequency of Gabors seen on previous trials. These two influences, which work on very different time scales, were approximately additive in their effects, each operating as an attractor for remembered appearance. Experiment 3 showed that a timely pre-stimulus cue allowed selective attention to curtail the influence of a task-irrelevant non-target, without diminishing the impact of the stimuli seen on previous trials. It appears that these two separable attractors influence distinct processes, with perception being influenced by the non-target stimulus and memory being influenced by stimuli seen on previous trials.

Real-time and quantitative isotropic spatial resolution susceptibility imaging for magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Pi, Shiqiang; Liu, Wenzhong; Jiang, Tao

2018-03-01

The magnetic transparency of biological tissue allows the magnetic nanoparticle (MNP) to be a promising functional sensor and contrast agent. The complex susceptibility of MNPs, strongly influenced by particle concentration, excitation magnetic field and their surrounding microenvironment, provides significant implications for biomedical applications. Therefore, magnetic susceptibility imaging of high spatial resolution will give more detailed information during the process of MNP-aided diagnosis and therapy. In this study, we present a novel spatial magnetic susceptibility extraction method for MNPs under a gradient magnetic field, a low-frequency drive magnetic field, and a weak strength high-frequency magnetic field. Based on this novel method, a magnetic particle susceptibility imaging (MPSI) of millimeter-level spatial resolution (<3 mm) was achieved using our homemade imaging system. Corroborated by the experimental results, the MPSI shows real-time (1 s per frame acquisition) and quantitative abilities, and isotropic high resolution.

Radiographic applications of spatial frequency multiplexing

NASA Technical Reports Server (NTRS)

Macovski, A.

1981-01-01

The application of spacial frequency encoding techniques which allow different regions of the X-ray spectrum to be encoded on conventional radiographs was studied. Clinical considerations were reviewed, as were experimental studies involving the encoding and decoding of X-ray images at different energies and the subsequent processing of the data to produce images of specific materials in the body.

Modelling the dependence of contrast sensitivity on grating area and spatial frequency.

PubMed

Rovamo, J; Luntinen, O; Näsänen, R

1993-12-01

We modelled the human foveal visual system in a detection task as a simple image processor comprising (i) low-pass filtering due to the optical transfer function of the eye, (ii) high-pass filtering of neural origin, (iii) addition of internal neural noise, and (iv) detection by a local matched filter. Its detection efficiency for gratings was constant up to a critical area but then decreased with increasing area. To test the model we measured Michelson contrast sensitivity as a function of grating area at spatial frequencies of 0.125-32 c/deg for simple vertical and circular cosine gratings. In circular gratings luminance was sinusoidally modulated as a function of the radius of the grating field. In agreement with the model, contrast sensitivity at all spatial frequencies increased in proportion to the square-root of grating area at small areas. When grating area exceeded critical area, the increase saturated and contrast sensitivity became independent of area at large grating areas. Spatial integration thus obeyed Piper's law at small grating areas. The critical area of spatial integration, marking the cessation of Piper's law, was constant in solid degrees at low spatial frequencies but inversely proportional to spatial frequency squared at medium and high spatial frequencies. At low spatial frequencies the maximum contrast sensitivity obtainable by spatial integration increased in proportion to spatial frequency but at high spatial frequencies it decreased in proportion to the cube of the increasing spatial frequency. The increase was due to high-pass filtering of neural origin (lateral inhibition) and the decrease was mainly due to the optical transfer function of the eye. Our model explained 95% of the total variance of the contrast sensitivity data.

Spatially-Heterodyned Holography

DOEpatents

Thomas, Clarence E [Knoxville, TN; Hanson, Gregory R [Clinton, TN

2006-02-21

A method of recording a spatially low-frequency heterodyne hologram, including spatially heterodyne fringes for Fourier analysis, includes: splitting a laser beam into a reference beam and an object beam; interacting the object beam with an object; focusing the reference beam and the object beam at a focal plane of a digital recorder to form a spatially low-frequency heterodyne hologram including spatially heterodyne fringes for Fourier analysis; digital recording the spatially low-frequency heterodyne hologram; Fourier transforming axes of the recorded spatially low-frequency heterodyne hologram including spatially heterodyne fringes in Fourier space to sit on top of a heterodyne carrier frequency defined by an angle between the reference beam and the object beam; cutting off signals around an origin; and performing an inverse Fourier transform.

Design trade-off between spatial resolution and power consumption in CMOS biosensor circuit based on millimeter-wave LC oscillator array

NASA Astrophysics Data System (ADS)

Matsunaga, Maya; Kobayashi, Atsuki; Nakazato, Kazuo; Niitsu, Kiichi

2018-03-01

In this paper, we describe a trade-off between spatial resolution and power consumption in an LC oscillator-based CMOS biosensor, which can detect biomolecules by observing the resonance frequency shift due to changes in the complex permittivity of the biomolecules. The optimal operating frequency and improvement in the image resolution of the sensor output require a reduction in the size of the inductor. However, it is necessary to increase the transconductance of the cross-coupling transistor to achieve the oscillation condition, although the power consumption increases. We confirmed the trade-off between the spatial resolution and the power consumption of this sensor using SPICE simulation. A test chip was fabricated using a 65 nm CMOS process, and the transition in the peak frequency and the power consumption were measured. When the outer diameter of the inductor was 46 µm, the power consumption was 31.2 mW, which matched well with the simulation results.

Statistical analysis of the surface figure of the James Webb Space Telescope

NASA Astrophysics Data System (ADS)

Lightsey, Paul A.; Chaney, David; Gallagher, Benjamin B.; Brown, Bob J.; Smith, Koby; Schwenker, John

2012-09-01

The performance of an optical system is best characterized by either the point spread function (PSF) or the optical transfer function (OTF). However, for system budgeting purposes, it is convenient to use a single scalar metric, or a combination of a few scalar metrics to track performance. For the James Webb Space Telescope, the Observatory level requirements were expressed in metrics of Strehl Ratio, and Encircled Energy. These in turn were converted to the metrics of total rms WFE and rms WFE within spatial frequency domains. The 18 individual mirror segments for the primary mirror segment assemblies (PMSA), the secondary mirror (SM), tertiary mirror (TM), and Fine Steering Mirror have all been fabricated. They are polished beryllium mirrors with a protected gold reflective coating. The statistical analysis of the resulting Surface Figure Error of these mirrors has been analyzed. The average spatial frequency distribution and the mirror-to-mirror consistency of the spatial frequency distribution are reported. The results provide insight to system budgeting processes for similar optical systems.

Spectral and energy characteristics of four-photon parametric scattering in sodium vapor

NASA Astrophysics Data System (ADS)

Vaicaitis, V.; Ignatavicius, M.; Kudriashov, V. A.; Pimenov, Iu. N.; Jakyte, R.

1987-04-01

Consideration is given to processes of four-photon interaction upon two-photon resonance excitation of the 3d level of sodium by two-frequency radiation from a monopulse picosecond YAG:Nd laser with frequency doubling and an optical parametric oscillator utilizing KDP crystrals. The spatial and frequency spectra of the four-photon parametric scattering (FPS) are recorded and studied at different sodium vapor concentrations (10 to the 15th to 10 to the 17th/cu cm) and upon both collinear and noncollinear excitation. It is shown that the observed conical structure of the FPS radiation can be interpreted from an analysis of the realization of the frequency and spatial phase-matching conditions. The dependences of the FPS radiation intensity on the exciting radiation intensity, the sodium vapor concentration, and the mismatching of the exciting radiation from the two-photon resonance are obtained.

Local sensitivity to stimulus orientation and spatial frequency within the receptive fields of neurons in visual area 2 of macaque monkeys

PubMed Central

Tao, X.; Zhang, B.; Smith, E. L.; Nishimoto, S.; Ohzawa, I.

2012-01-01

We used dynamic dense noise stimuli and local spectral reverse correlation methods to reveal the local sensitivities of neurons in visual area 2 (V2) of macaque monkeys to orientation and spatial frequency within their receptive fields. This minimized the potentially confounding assumptions that are inherent in stimulus selections. The majority of neurons exhibited a relatively high degree of homogeneity for the preferred orientations and spatial frequencies in the spatial matrix of facilitatory subfields. However, about 20% of all neurons showed maximum orientation differences between neighboring subfields that were greater than 25 deg. The neurons preferring horizontal or vertical orientations showed less inhomogeneity in space than the neurons preferring oblique orientations. Over 50% of all units also exhibited suppressive profiles, and those were more heterogeneous than facilitatory profiles. The preferred orientation and spatial frequency of suppressive profiles differed substantially from those of facilitatory profiles, and the neurons with suppressive subfields had greater orientation selectivity than those without suppressive subfields. The peak suppression occurred with longer delays than the peak facilitation. These results suggest that the receptive field profiles of the majority of V2 neurons reflect the orderly convergence of V1 inputs over space, but that a subset of V2 neurons exhibit more complex response profiles having both suppressive and facilitatory subfields. These V2 neurons with heterogeneous subfield profiles could play an important role in the initial processing of complex stimulus features. PMID:22114163

Simultaneous storage of medical images in the spatial and frequency domain: A comparative study

PubMed Central

Nayak, Jagadish; Bhat, P Subbanna; Acharya U, Rajendra; UC, Niranjan

2004-01-01

Background Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. Methods The patient information is encrypted before interleaving with images to ensure greater security. The bio-signals are compressed and subsequently interleaved with the image. This interleaving is carried out in the spatial domain and Frequency domain. The performance of interleaving in the spatial, Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) coefficients is studied. Differential pulse code modulation (DPCM) is employed for data compression as well as encryption and results are tabulated for a specific example. Results It can be seen from results, the process does not affect the picture quality. This is attributed to the fact that the change in LSB of a pixel changes its brightness by 1 part in 256. Spatial and DFT domain interleaving gave very less %NRMSE as compared to DCT and DWT domain. Conclusion The Results show that spatial domain the interleaving, the %NRMSE was less than 0.25% for 8-bit encoded pixel intensity. Among the frequency domain interleaving methods, DFT was found to be very efficient. PMID:15180899

Arrhythmia Mechanism and Scaling Effect on the Spectral Properties of Electroanatomical Maps With Manifold Harmonics.

PubMed

Sanroman-Junquera, Margarita; Mora-Jimenez, Inmaculada; Garcia-Alberola, Arcadio; Caamano, Antonio J; Trenor, Beatriz; Rojo-Alvarez, Jose L

2018-04-01

Spatial and temporal processing of intracardiac electrograms provides relevant information to support the arrhythmia ablation during electrophysiological studies. Current cardiac navigation systems (CNS) and electrocardiographic imaging (ECGI) build detailed 3-D electroanatomical maps (EAM), which represent the spatial anatomical distribution of bioelectrical features, such as activation time or voltage. We present a principled methodology for spectral analysis of both EAM geometry and bioelectrical feature in CNS or ECGI, including their spectral representation, cutoff frequency, or spatial sampling rate (SSR). Existing manifold harmonic techniques for spectral mesh analysis are adapted to account for a fourth dimension, corresponding to the EAM bioelectrical feature. Appropriate scaling is required to address different magnitudes and units. With our approach, simulated and real EAM showed strong SSR dependence on both the arrhythmia mechanism and the cardiac anatomical shape. For instance, high frequencies increased significantly the SSR because of the "early-meets-late" in flutter EAM, compared with the sinus rhythm. Besides, higher frequency components were obtained for the left atrium (more complex anatomy) than for the right atrium in sinus rhythm. The proposed manifold harmonics methodology opens the field toward new signal processing tools for principled EAM spatiofeature analysis in CNS and ECGI, and to an improved knowledge on arrhythmia mechanisms.

GPS data processing of networks with mixed single- and dual-frequency receivers for deformation monitoring

NASA Astrophysics Data System (ADS)

Zou, X.; Deng, Z.; Ge, M.; Dick, G.; Jiang, W.; Liu, J.

2010-07-01

In order to obtain crustal deformations of higher spatial resolution, existing GPS networks must be densified. This densification can be carried out using single-frequency receivers at moderate costs. However, ionospheric delay handling is required in the data processing. We adapt the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) for GPS networks with mixed single- and dual-frequency receivers. The SEID model is modified to utilize the observations from the three nearest dual-frequency reference stations in order to avoid contaminations from more remote stations. As data of only three stations are used, an efficient missing data constructing approach with polynomial fitting is implemented to minimize data losses. Data from large scale reference networks extended with single-frequency receivers can now be processed, based on the adapted SEID model. A new data processing scheme is developed in order to make use of existing GPS data processing software packages without any modifications. This processing scheme is evaluated using a sub-network of the German SAPOS network. The results verify that the new scheme provides an efficient way to densify existing GPS networks with single-frequency receivers.

Evolution of spatial and temporal correlations in the solar wind - Observations and interpretation

NASA Technical Reports Server (NTRS)

Klein, L. W.; Matthaeus, W. H.; Roberts, D. A.; Goldstein, M. L.

1992-01-01

Observations of solar wind magnetic field spectra from 1-22 AU indicate a distinctive structure in frequency which evolves with increasing heliocentric distance. At 1 AU extremely low frequency correlations are associated with temporal variations at the solar period and its first few harmonics. For periods of l2-96 hours, a l/f distribution is observed, which we interpret as an aggregate of uncorrelated coronal structures which have not dynamically interacted by 1 AU. At higher frequencies the familiar Kolmogorov-like power law is seen. Farther from the sun the frequency break point between the shallow l/f and the steeper Kolmogorov spectrum evolves systematically towards lower frequencies. We suggest that the Kolmogorov-like spectra emerge due to in situ turbulence that generates spatial correlations associated with the turbulent cascade and that the background l/f noise is a largely temporal phenomenon, not associated with in situ dynamical processes. In this paper we discuss these ideas from the standpoint of observations from several interplanetary spacecraft.

Basic data features and results from a spatially dense seismic array on the San Jacinto fault zone

NASA Astrophysics Data System (ADS)

Ben-Zion, Yehuda; Vernon, Frank L.; Ozakin, Yaman; Zigone, Dimitri; Ross, Zachary E.; Meng, Haoran; White, Malcolm; Reyes, Juan; Hollis, Dan; Barklage, Mitchell

2015-07-01

We discuss several outstanding aspects of seismograms recorded during >4 weeks by a spatially dense Nodal array, straddling the damage zone of the San Jacinto fault in southern California, and some example results. The waveforms contain numerous spikes and bursts of high-frequency waves (up to the recorded 200 Hz) produced in part by minute failure events in the shallow crust. The high spatial density of the array facilitates the detection of 120 small local earthquakes in a single day, most of which not detected by the surrounding ANZA and regional southern California networks. Beamforming results identify likely ongoing cultural noise sources dominant in the frequency range 1-10 Hz and likely ongoing earthquake sources dominant in the frequency range 20-40 Hz. Matched-field processing and back-projection of seismograms provide alternate event location. The median noise levels during the experiment at different stations, waves generated by Betsy gunshots, and wavefields from nearby earthquakes point consistently to several structural units across the fault. Seismic trapping structure and local sedimentary basin produce localized motion amplification and stronger attenuation than adjacent regions. Cross correlations of high-frequency noise recorded at closely spaced stations provide a structural image of the subsurface material across the fault zone. The high spatial density and broad frequency range of the data can be used for additional high resolution studies of structure and source properties in the shallow crust.

Parameters influencing focalization spot in time reversal of acoustic waves

NASA Astrophysics Data System (ADS)

Zophoniasson, Harald; Bolzmacher, Christian; Hafez, Moustafa

2015-05-01

Time reversal is an approach that can be used to focus acoustic waves in a particular location on a surface, allowing a multitouch tactile feedback interaction. The spatial resolution in this case depends on several parameters, such as geometrical parameters, frequency used and material properties, described by the Lamb wave theory. This paper highlights the impact of frequency, geometrical parameters such as plate thickness and transducer's surface on the focused spot dimensions. In this paper a study of the influence of the plate's thickness and the frequency bandwidth used in the focusing process is presented. It is also shown that the dimension of the piezoelectric diaphragms used has little influence on the spatial resolution. Resonant behavior of the plate and its implication on focus point dimension and focalization contrast were investigated.

Effective connectivity in the neural network underlying coarse-to-fine categorization of visual scenes. A dynamic causal modeling study.

PubMed

Kauffmann, Louise; Chauvin, Alan; Pichat, Cédric; Peyrin, Carole

2015-10-01

According to current models of visual perception scenes are processed in terms of spatial frequencies following a predominantly coarse-to-fine processing sequence. Low spatial frequencies (LSF) reach high-order areas rapidly in order to activate plausible interpretations of the visual input. This triggers top-down facilitation that guides subsequent processing of high spatial frequencies (HSF) in lower-level areas such as the inferotemporal and occipital cortices. However, dynamic interactions underlying top-down influences on the occipital cortex have never been systematically investigated. The present fMRI study aimed to further explore the neural bases and effective connectivity underlying coarse-to-fine processing of scenes, particularly the role of the occipital cortex. We used sequences of six filtered scenes as stimuli depicting coarse-to-fine or fine-to-coarse processing of scenes. Participants performed a categorization task on these stimuli (indoor vs. outdoor). Firstly, we showed that coarse-to-fine (compared to fine-to-coarse) sequences elicited stronger activation in the inferior frontal gyrus (in the orbitofrontal cortex), the inferotemporal cortex (in the fusiform and parahippocampal gyri), and the occipital cortex (in the cuneus). Dynamic causal modeling (DCM) was then used to infer effective connectivity between these regions. DCM results revealed that coarse-to-fine processing resulted in increased connectivity from the occipital cortex to the inferior frontal gyrus and from the inferior frontal gyrus to the inferotemporal cortex. Critically, we also observed an increase in connectivity strength from the inferior frontal gyrus to the occipital cortex, suggesting that top-down influences from frontal areas may guide processing of incoming signals. The present results support current models of visual perception and refine them by emphasizing the role of the occipital cortex as a cortical site for feedback projections in the neural network underlying coarse-to-fine processing of scenes. Copyright © 2015 Elsevier Inc. All rights reserved.

Spatial gradient for unique-feature detection in patients with unilateral neglect: evidence from auditory and visual search.

PubMed

Eramudugolla, Ranmalee; Mattingley, Jason B

2008-01-01

Patients with unilateral spatial neglect following right hemisphere damage are impaired in detecting contralesional targets in both visual and haptic search tasks, and often show a graded improvement in detection performance for more ipsilesional spatial locations. In audition, multiple simultaneous sounds are most effectively perceived if they are distributed along the frequency dimension. Thus, attention to spectro-temporal features alone can allow detection of a target sound amongst multiple simultaneous distracter sounds, regardless of whether these sounds are spatially separated. Spatial bias in attention associated with neglect should not affect auditory search based on spectro-temporal features of a sound target. We report that a right brain damaged patient with neglect demonstrated a significant gradient favouring the ipsilesional side on a visual search task as well as an auditory search task in which the target was a frequency modulated tone amongst steady distractor tones. No such asymmetry was apparent in the auditory search performance of a control patient with a right hemisphere lesion but no neglect. The results suggest that the spatial bias in attention exhibited by neglect patients affects stimulus processing even when spatial information is irrelevant to the task.

Coarse-to-Fine Encoding of Spatial Frequency Information into Visual Short-Term Memory for Faces but Impartial Decay

ERIC Educational Resources Information Center

Gao, Zaifeng; Bentin, Shlomo

2011-01-01

Face perception studies investigated how spatial frequencies (SF) are extracted from retinal display while forming a perceptual representation, or their selective use during task-imposed categorization. Here we focused on the order of encoding low-spatial frequencies (LSF) and high-spatial frequencies (HSF) from perceptual representations into…

Representational dynamics of object recognition: Feedforward and feedback information flows.

PubMed

Goddard, Erin; Carlson, Thomas A; Dermody, Nadene; Woolgar, Alexandra

2016-03-01

Object perception involves a range of visual and cognitive processes, and is known to include both a feedfoward flow of information from early visual cortical areas to higher cortical areas, along with feedback from areas such as prefrontal cortex. Previous studies have found that low and high spatial frequency information regarding object identity may be processed over different timescales. Here we used the high temporal resolution of magnetoencephalography (MEG) combined with multivariate pattern analysis to measure information specifically related to object identity in peri-frontal and peri-occipital areas. Using stimuli closely matched in their low-level visual content, we found that activity in peri-occipital cortex could be used to decode object identity from ~80ms post stimulus onset, and activity in peri-frontal cortex could also be used to decode object identity from a later time (~265ms post stimulus onset). Low spatial frequency information related to object identity was present in the MEG signal at an earlier time than high spatial frequency information for peri-occipital cortex, but not for peri-frontal cortex. We additionally used Granger causality analysis to compare feedforward and feedback influences on representational content, and found evidence of both an early feedfoward flow and later feedback flow of information related to object identity. We discuss our findings in relation to existing theories of object processing and propose how the methods we use here could be used to address further questions of the neural substrates underlying object perception. Copyright © 2016 Elsevier Inc. All rights reserved.

Mid-frequency MTF compensation of optical sparse aperture system.

PubMed

Zhou, Chenghao; Wang, Zhile

2018-03-19

Optical sparse aperture (OSA) can greatly improve the spatial resolution of optical system. However, because of its aperture dispersion and sparse, its mid-frequency modulation transfer function (MTF) are significantly lower than that of a single aperture system. The main focus of this paper is on the mid-frequency MTF compensation of the optical sparse aperture system. Firstly, the principle of the mid-frequency MTF decreasing and missing of optical sparse aperture are analyzed. This paper takes the filling factor as a clue. The method of processing the mid-frequency MTF decreasing with large filling factor and method of compensation mid-frequency MTF with small filling factor are given respectively. For the MTF mid-frequency decreasing, the image spatial-variant restoration method is proposed to restore the mid-frequency information in the image; for the mid-frequency MTF missing, two images obtained by two system respectively are fused to compensate the mid-frequency information in optical sparse aperture image. The feasibility of the two method are analyzed in this paper. The numerical simulation of the system and algorithm of the two cases are presented using Zemax and Matlab. The results demonstrate that by these two methods the mid-frequency MTF of OSA system can be compensated effectively.

Improving demodulation accuracy of low-coherence interferometer against spatial-frequency nonlinearity

NASA Astrophysics Data System (ADS)

Wang, Shuang; Liu, Tiegen; Jiang, Junfeng; Liu, Kun; Yin, Jinde; Wu, Fan; Zhao, Bofu; Xue, Lei; Mei, Yunqiao; Wu, Zhenhai

2013-12-01

We present an effective method to compensate the spatial-frequency nonlinearity for polarized low-coherence interferometer with location-dependent dispersion element. Through the use of location-dependent dispersive characteristics, the method establishes the exact relationship between wave number and discrete Fourier transform (DFT) serial number. The jump errors in traditional absolute phase algorithm are also avoided with nonlinearity compensation. We carried out experiments with an optical fiber Fabry-Perot (F-P) pressure sensing system to verify the effectiveness. The demodulated error is less than 0.139kPa in the range of 170kPa when using our nonlinearity compensation process in the demodulation.

Perceptual dehumanization of faces is activated by norm violations and facilitates norm enforcement.

PubMed

Fincher, Katrina M; Tetlock, Philip E

2016-02-01

This article uses methods drawn from perceptual psychology to answer a basic social psychological question: Do people process the faces of norm violators differently from those of others--and, if so, what is the functional significance? Seven studies suggest that people process these faces different and the differential processing makes it easier to punish norm violators. Studies 1 and 2 use a recognition-recall paradigm that manipulated facial-inversion and spatial frequency to show that people rely upon face-typical processing less when they perceive norm violators' faces. Study 3 uses a facial composite task to demonstrate that the effect is actor dependent, not action dependent, and to suggest that configural processing is the mechanism of perceptual change. Studies 4 and 5 use offset faces to show that configural processing is only attenuated when they belong to perpetrators who are culpable. Studies 6 and 7 show that people find it easier to punish inverted faces and harder to punish faces displayed in low spatial frequency. Taken together, these data suggest a bidirectional flow of causality between lower-order perceptual and higher-order cognitive processes in norm enforcement. PsycINFO Database Record (c) 2016 APA, all rights reserved.

Process Inference from High Frequency Temporal Variations in Dissolved Organic Carbon (DOC) Dynamics Across Nested Spatial Scales

NASA Astrophysics Data System (ADS)

Tunaley, C.; Tetzlaff, D.; Lessels, J. S.; Soulsby, C.

2014-12-01

In order to understand aquatic ecosystem functioning it is critical to understand the processes that control the spatial and temporal variations in DOC. DOC concentrations are highly dynamic, however, our understanding at short, high frequency timescales is still limited. Optical sensors which act as a proxy for DOC provide the opportunity to investigate near-continuous DOC variations in order to understand the hydrological and biogeochemical processes that control concentrations at short temporal scales. Here we present inferred 15 minute stream water DOC data for a 12 month period at three nested scales (1km2, 3km2 and 31km2) for the Bruntland Burn, a headwater catchment in NE Scotland. High frequency data were measured using FDOM and CDOM probes which work by measuring the fluorescent component and coloured component, respectively, of DOC when exposed to ultraviolet light. Both FDOM and CDOM were strongly correlated (r2 >0.8) with DOC allowing high frequency estimations. Results show the close coupling of DOC with discharge throughout the sampling period at all three spatial scales. However, analysis at the event scale highlights anticlockwise hysteresis relationships between DOC and discharge due to the delay in DOC being flushed from the increasingly large areas of peaty soils as saturation zones expand and increase hydrological connectivity. Lag times vary between events dependent on antecedent conditions. During a 10 year drought period in late summer 2013 it was apparent that very small changes in discharge on a 15 minute timescale result in high increases in DOC. This suggests transport limitation during this period where DOC builds up in the soil and is not flushed regularly, therefore any subsequent increase in discharge results in large DOC peaks. The high frequency sensors also reveal diurnal variability during summer months related to the photo-oxidation, evaporative and biological influences of DOC during the day. This relationship is less significant during the winter months.

Neutral processes contribute to patterns of spatial variation for flower colour in the Mediterranean Iris lutescens (Iridaceae)

PubMed Central

Wang, Hui; Talavera, María; Min, Ya; Flaven, Elodie; Imbert, Eric

2016-01-01

Background and Aims Flower colour polymorphism in plants has been used as a classic model for understanding the importance of neutral processes vs. natural selection in population differentiation. However, current explanations for the maintenance of flower colour polymorphism mainly rely on balancing selection, while neutral processes have seldom been championed. Iris lutescens (Iridaceae) is a widespread species in the northern Mediterranean basin, which shows a stable and striking purple–yellow flower colour polymorphism. To evaluate the roles of neutral processes in the spatial variation for flower colour in this species, patterns of neutral genetic variation across its distribution range were quantified, and phenotypic differentiation was compared with neutral genetic differentiation. Methods Genetic diversity levels and population genetic structure were investigated through the genotyping of a collection of 1120 individuals in 41 populations ranging from Spain to France, using a set of eight newly developed microsatellite markers. In addition, phenotypic differentiation for flower colour was also quantified by counting colour morph frequency in each population, and measuring the reflectance spectra of sampled individuals. Key Results Populations in Spain present a sharp colour transition from solely purple to solely yellow. The results provide evidence that genetic drift through limited gene flow is important in the evolution of monomorphic populations. In contrast, most populations in France are polymorphic with both phenotypes, and the colour frequencies vary geographically without any spatial gradients observed. A pattern of isolation by distance is detected in France, and gene flow between adjacent populations seems to be an important factor maintaining populations polymorphic. Conclusions Overall, neutral processes contribute to patterns of spatial variation for flower colour in I. lutescens, but it cannot be excluded that natural selection is also operating. An interaction between neutral processes and natural selection is suggested to explain the spatial variation for flower colour in I. lutescens. PMID:27084922

Neutral processes contribute to patterns of spatial variation for flower colour in the Mediterranean Iris lutescens (Iridaceae).

PubMed

Wang, Hui; Talavera, María; Min, Ya; Flaven, Elodie; Imbert, Eric

2016-05-01

Flower colour polymorphism in plants has been used as a classic model for understanding the importance of neutral processes vs. natural selection in population differentiation. However, current explanations for the maintenance of flower colour polymorphism mainly rely on balancing selection, while neutral processes have seldom been championed. Iris lutescens (Iridaceae) is a widespread species in the northern Mediterranean basin, which shows a stable and striking purple-yellow flower colour polymorphism. To evaluate the roles of neutral processes in the spatial variation for flower colour in this species, patterns of neutral genetic variation across its distribution range were quantified, and phenotypic differentiation was compared with neutral genetic differentiation. Genetic diversity levels and population genetic structure were investigated through the genotyping of a collection of 1120 individuals in 41 populations ranging from Spain to France, using a set of eight newly developed microsatellite markers. In addition, phenotypic differentiation for flower colour was also quantified by counting colour morph frequency in each population, and measuring the reflectance spectra of sampled individuals. Populations in Spain present a sharp colour transition from solely purple to solely yellow. The results provide evidence that genetic drift through limited gene flow is important in the evolution of monomorphic populations. In contrast, most populations in France are polymorphic with both phenotypes, and the colour frequencies vary geographically without any spatial gradients observed. A pattern of isolation by distance is detected in France, and gene flow between adjacent populations seems to be an important factor maintaining populations polymorphic. Overall, neutral processes contribute to patterns of spatial variation for flower colour in I. lutescens, but it cannot be excluded that natural selection is also operating. An interaction between neutral processes and natural selection is suggested to explain the spatial variation for flower colour in I. lutescens. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Low spatial frequency characterization of holographic recording materials applied to correlation

NASA Astrophysics Data System (ADS)

Márquez, A.; Neipp, C.; Beléndez, A.; Campos, J.; Pascual, I.; Yzuel, M. J.; Fimia, A.

2003-09-01

Accurate recording of computer-generated holograms (CGH) on a phase material is not a trivial task. The range of available phase materials is large, and their suitability depends on the fabrication technique chosen to produce the hologram. We are particularly interested in low-cost fabrication techniques, easily available for any lab. In this work we present the results obtained with a wide variety of phase holographic recording materials, characterized at low spatial frequencies (leq32 lp mm-1) which is the range associated with the technique we use to produce the CGHs. We have considered bleached emulsion, silver halide sensitized gelatin (SHSG) and dichromated gelatin. Some interesting differences arise between the behaviour of these materials in the usual holographic range (>1000 lp mm-1), and the low-frequency range intended for digital holography. The ultimate goal of this paper is to establish the suitability of different phase materials as the media to generate correlation filters for optical pattern recognition. In all the materials considered, the phase filters generated ensure the discrimination of the target in the recognition process. Taking into account all the experimental results, we can say that SHSG is the best material to generate phase CGHs with low spatial frequencies.

Spatial Frequency Selectivity Is Impaired in Dopamine D2 Receptor Knockout Mice

PubMed Central

Souza, Bruno Oliveira Ferreira; Abou Rjeili, Mira; Quintana, Clémentine; Beaulieu, Jean M.; Casanova, Christian

2018-01-01

Dopamine is a neurotransmitter implicated in several brain functions, including vision. In the present study, we investigated the impacts of the lack of D2 dopamine receptors on the structure and function of the primary visual cortex (V1) of D2-KO mice using optical imaging of intrinsic signals. Retinotopic maps were generated in order to measure anatomo-functional parameters such as V1 shape, cortical magnification factor, scatter, and ocular dominance. Contrast sensitivity and spatial frequency selectivity (SF) functions were computed from responses to drifting gratings. When compared to control mice, none of the parameters of the retinotopic maps were affected by D2 receptor loss of function. While the contrast sensitivity function of D2-KO mice did not differ from their wild-type counterparts, SF selectivity function was significantly affected as the optimal SF and the high cut-off frequency (p < 0.01) were higher in D2-KO than in WT mice. These findings show that the lack of function of D2 dopamine receptors had no influence on cortical structure whereas it had a significant impact on the spatial frequency selectivity and high cut-off. Taken together, our results suggest that D2 receptors play a specific role on the processing of spatial features in early visual cortex while they do not seem to participate in its development. PMID:29379422

Periodicity of the density wake past a vortex ring in a stratified liquid

NASA Astrophysics Data System (ADS)

Prokhorov, V.

2009-04-01

Spatial coherent structure of the density wake past a vortex ring moving horizontally in viscid stratified liquid is experimentally revealed. It follows from analysis that repetition period of the structure is determined by rotation radial frequency (or mean vorticity) of the vortex core and toward speed of the vortex ring. The wake formation of the ring is considered in respect to vorticity shedding which produces velocity disturbances in ambient medium. In case of stratified liquid velocity fluctuations, in their turn, cause density field distortion. This process is superimposed by vortex core oscillations, and, in result, vorticity shedding will be not monotonous but modulated at some frequency. So, the density wake is periodically structured, and the spatial period is defined by intrinsic frequency of the core and forward speed of the ring. To support analysis, experiments were conducted in which vortex rings excited by spring-piston generator were observed with high-sensitive Schlieren instrument and computer-controlled camera. Experimental tank was filled with salt-stratified water of constant buoyancy period, vortex ring velocities range from 3 to 16 cm/s. Spatial period is derived from schlieren image using two independent methods, both 2D spectral analysis and geometry calculations of the vortex core. Spatial periods and vortex intrinsic frequencies calculated by both algorithms are in good agreement; they vary in power lows depending on vortex speed

High-Frequency Subband Compressed Sensing MRI Using Quadruplet Sampling

PubMed Central

Sung, Kyunghyun; Hargreaves, Brian A

2013-01-01

Purpose To presents and validates a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data. Theory and Methods High- and low-spatial-frequency regions are defined in k-space based on the separation of wavelet subbands, and the conventional compressed sensing (CS) problem is transformed into one of localized k-space estimation. To better exploit wavelet-domain sparsity, CS can be used for high-spatial-frequency regions while parallel imaging can be used for low-spatial-frequency regions. Fourier undersampling is also customized to better accommodate each reconstruction method: random undersampling for CS and regular undersampling for parallel imaging. Results Examples using the proposed method demonstrate successful reconstruction of both low-spatial-frequency content and fine structures in high-resolution 3D breast imaging with a net acceleration of 11 to 12. Conclusion The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size. PMID:23280540

Spatial frequency discrimination learning in normal and developmentally impaired human vision

PubMed Central

Astle, Andrew T.; Webb, Ben S.; McGraw, Paul V.

2010-01-01

Perceptual learning effects demonstrate that the adult visual system retains neural plasticity. If perceptual learning holds any value as a treatment tool for amblyopia, trained improvements in performance must generalise. Here we investigate whether spatial frequency discrimination learning generalises within task to other spatial frequencies, and across task to contrast sensitivity. Before and after training, we measured contrast sensitivity and spatial frequency discrimination (at a range of reference frequencies 1, 2, 4, 8, 16 c/deg). During training, normal and amblyopic observers were divided into three groups. Each group trained on a spatial frequency discrimination task at one reference frequency (2, 4, or 8 c/deg). Normal and amblyopic observers who trained at lower frequencies showed a greater rate of within task learning (at their reference frequency) compared to those trained at higher frequencies. Compared to normals, amblyopic observers showed greater within task learning, at the trained reference frequency. Normal and amblyopic observers showed asymmetrical transfer of learning from high to low spatial frequencies. Both normal and amblyopic subjects showed transfer to contrast sensitivity. The direction of transfer for contrast sensitivity measurements was from the trained spatial frequency to higher frequencies, with the bandwidth and magnitude of transfer greater in the amblyopic observers compared to normals. The findings provide further support for the therapeutic efficacy of this approach and establish general principles that may help develop more effective protocols for the treatment of developmental visual deficits. PMID:20832416

A study of digital holographic filter generation

NASA Technical Reports Server (NTRS)

Calhoun, M.; Ingels, F.

1976-01-01

Problems associated with digital computer generation of holograms are discussed along with a criteria for producing optimum digital holograms. This criteria revolves around amplitude resolution and spatial frequency limitations induced by the computer and plotter process.

Multiple-Parameter Estimation Method Based on Spatio-Temporal 2-D Processing for Bistatic MIMO Radar

PubMed Central

Yang, Shouguo; Li, Yong; Zhang, Kunhui; Tang, Weiping

2015-01-01

A novel spatio-temporal 2-dimensional (2-D) processing method that can jointly estimate the transmitting-receiving azimuth and Doppler frequency for bistatic multiple-input multiple-output (MIMO) radar in the presence of spatial colored noise and an unknown number of targets is proposed. In the temporal domain, the cross-correlation of the matched filters’ outputs for different time-delay sampling is used to eliminate the spatial colored noise. In the spatial domain, the proposed method uses a diagonal loading method and subspace theory to estimate the direction of departure (DOD) and direction of arrival (DOA), and the Doppler frequency can then be accurately estimated through the estimation of the DOD and DOA. By skipping target number estimation and the eigenvalue decomposition (EVD) of the data covariance matrix estimation and only requiring a one-dimensional search, the proposed method achieves low computational complexity. Furthermore, the proposed method is suitable for bistatic MIMO radar with an arbitrary transmitted and received geometrical configuration. The correction and efficiency of the proposed method are verified by computer simulation results. PMID:26694385

Multiple-Parameter Estimation Method Based on Spatio-Temporal 2-D Processing for Bistatic MIMO Radar.

PubMed

Yang, Shouguo; Li, Yong; Zhang, Kunhui; Tang, Weiping

2015-12-14

A novel spatio-temporal 2-dimensional (2-D) processing method that can jointly estimate the transmitting-receiving azimuth and Doppler frequency for bistatic multiple-input multiple-output (MIMO) radar in the presence of spatial colored noise and an unknown number of targets is proposed. In the temporal domain, the cross-correlation of the matched filters' outputs for different time-delay sampling is used to eliminate the spatial colored noise. In the spatial domain, the proposed method uses a diagonal loading method and subspace theory to estimate the direction of departure (DOD) and direction of arrival (DOA), and the Doppler frequency can then be accurately estimated through the estimation of the DOD and DOA. By skipping target number estimation and the eigenvalue decomposition (EVD) of the data covariance matrix estimation and only requiring a one-dimensional search, the proposed method achieves low computational complexity. Furthermore, the proposed method is suitable for bistatic MIMO radar with an arbitrary transmitted and received geometrical configuration. The correction and efficiency of the proposed method are verified by computer simulation results.

Fast convergent frequency-domain MIMO equalizer for few-mode fiber communication systems

NASA Astrophysics Data System (ADS)

He, Xuan; Weng, Yi; Wang, Junyi; Pan, Z.

2018-02-01

Space division multiplexing using few-mode fibers has been extensively explored to sustain the continuous traffic growth. In few-mode fiber optical systems, both spatial and polarization modes are exploited to transmit parallel channels, thus increasing the overall capacity. However, signals on spatial channels inevitably suffer from the intrinsic inter-modal coupling and large accumulated differential mode group delay (DMGD), which causes spatial modes de-multiplex even harder. Many research articles have demonstrated that frequency domain adaptive multi-input multi-output (MIMO) equalizer can effectively compensate the DMGD and demultiplex the spatial channels with digital signal processing (DSP). However, the large accumulated DMGD usually requires a large number of training blocks for the initial convergence of adaptive MIMO equalizers, which will decrease the overall system efficiency and even degrade the equalizer performance in fast-changing optical channels. Least mean square (LMS) algorithm is always used in MIMO equalization to dynamically demultiplex the spatial signals. We have proposed to use signal power spectral density (PSD) dependent method and noise PSD directed method to improve the convergence speed of adaptive frequency domain LMS algorithm. We also proposed frequency domain recursive least square (RLS) algorithm to further increase the convergence speed of MIMO equalizer at cost of greater hardware complexity. In this paper, we will compare the hardware complexity and convergence speed of signal PSD dependent and noise power directed algorithms against the conventional frequency domain LMS algorithm. In our numerical study of a three-mode 112 Gbit/s PDM-QPSK optical system with 3000 km transmission, the noise PSD directed and signal PSD dependent methods could improve the convergence speed by 48.3% and 36.1% respectively, at cost of 17.2% and 10.7% higher hardware complexity. We will also compare the frequency domain RLS algorithm against conventional frequency domain LMS algorithm. Our numerical study shows that, in a three-mode 224 Gbit/s PDM-16-QAM system with 3000 km transmission, the RLS algorithm could improve the convergence speed by 53.7% over conventional frequency domain LMS algorithm.

Will Brazilian Patented Naturoptic Method for Recovery of Healthy Vision be Helpful Linguistically?

NASA Astrophysics Data System (ADS)

de Moraes, Ana Paula; Dos Santos Marques, Rosélia; Mc Leod, Roger David

2008-10-01

Naturoptics Inc. extends its patent(s) to further the teaching of vision-restoring process(es), foster cross-linguistic capabilities, and assist in the educational or financial opportunities of individuals and countries. Directors of Naturoptics Inc. hope to achieve this while testing David Matthew Mc Leod's observations that high visual acuity correlates with other mental and sensory processes. He and RDM often noticed that thought concepts (language percepts) are detectable even across species barriers, as when bears, moose, et c. made their intentions known to us in ways we were culturally willing to accept. This addresses aspects of language that seemed related to our understanding of human vision, and how it encodes cortically by spatial frequency content of a visual scene. Words representing the same meaning in two different languages will encode at precisely the same site in the visual cortex. Predictions: ``our memories,'' and cross-species, detection of certain thoughts, if equivalently ``seen'' as images, (spatial frequency content).

Two stochastic models useful in petroleum exploration

NASA Technical Reports Server (NTRS)

Kaufman, G. M.; Bradley, P. G.

1972-01-01

A model of the petroleum exploration process that tests empirically the hypothesis that at an early stage in the exploration of a basin, the process behaves like sampling without replacement is proposed along with a model of the spatial distribution of petroleum reserviors that conforms to observed facts. In developing the model of discovery, the following topics are discussed: probabilitistic proportionality, likelihood function, and maximum likelihood estimation. In addition, the spatial model is described, which is defined as a stochastic process generating values of a sequence or random variables in a way that simulates the frequency distribution of areal extent, the geographic location, and shape of oil deposits

A periodic spatio-spectral filter for event-related potentials.

PubMed

Ghaderi, Foad; Kim, Su Kyoung; Kirchner, Elsa Andrea

2016-12-01

With respect to single trial detection of event-related potentials (ERPs), spatial and spectral filters are two of the most commonly used pre-processing techniques for signal enhancement. Spatial filters reduce the dimensionality of the data while suppressing the noise contribution and spectral filters attenuate frequency components that most likely belong to noise subspace. However, the frequency spectrum of ERPs overlap with that of the ongoing electroencephalogram (EEG) and different types of artifacts. Therefore, proper selection of the spectral filter cutoffs is not a trivial task. In this research work, we developed a supervised method to estimate the spatial and finite impulse response (FIR) spectral filters, simultaneously. We evaluated the performance of the method on offline single trial classification of ERPs in datasets recorded during an oddball paradigm. The proposed spatio-spectral filter improved the overall single-trial classification performance by almost 9% on average compared with the case that no spatial filters were used. We also analyzed the effects of different spectral filter lengths and the number of retained channels after spatial filtering. Copyright © 2016. Published by Elsevier Ltd.

Shortcomings of low-cost imaging systems for viewing computed radiographs.

PubMed

Ricke, J; Hänninen, E L; Zielinski, C; Amthauer, H; Stroszczynski, C; Liebig, T; Wolf, M; Hosten, N

2000-01-01

To assess potential advantages of a new PC-based viewing tool featuring image post-processing for viewing computed radiographs on low-cost hardware (PC) with a common display card and color monitor, and to evaluate the effect of using color versus monochrome monitors. Computed radiographs of a statistical phantom were viewed on a PC, with and without post-processing (spatial frequency and contrast processing), employing a monochrome or a color monitor. Findings were compared with the viewing on a radiological Workstation and evaluated with ROC analysis. Image post-processing improved the perception of low-contrast details significantly irrespective of the monitor used. No significant difference in perception was observed between monochrome and color monitors. The review at the radiological Workstation was superior to the review done using the PC with image processing. Lower quality hardware (graphic card and monitor) used in low cost PCs negatively affects perception of low-contrast details in computed radiographs. In this situation, it is highly recommended to use spatial frequency and contrast processing. No significant quality gain has been observed for the high-end monochrome monitor compared to the color display. However, the color monitor was affected stronger by high ambient illumination.

Facial expressions perceived by the adolescent brain: Towards the proficient use of low spatial frequency information.

PubMed

Peters, Judith C; Kemner, Chantal

2017-10-01

Rapid decoding of emotional expressions is essential for social communication. Fast processing of facial expressions depends on the adequate (subcortical) processing of important global face cues in the low spatial frequency (LSF) ranges. However, children below 9 years of age extract fearful expression information from local details represented by high SF (HSF) image content. Our ERP study investigated at which developmental stage this ineffective HSF-driven processing is replaced by the proficient and rapid LSF-driven perception of fearful faces, in which adults are highly skilled. We examined behavioral and neural responses to high- and low-pass filtered faces with a fearful or neutral expression in groups of children on the verge of pre-adolescence (9-10 years), adolescents (14-15 years), and young adults (20-28 years). Our results suggest that the neural emotional face processing network has a protracted maturational course into adolescence, which is related to changes in SF processing. In mid-adolescence, increased sensitivity to emotional LSF cues is developed, which aids the fast and adequate processing of fearful expressions that might signal impending danger. Copyright © 2017 Elsevier B.V. All rights reserved.

Improved line-end foreshortening and corner-rounding control in optical proximity correction using radius of curvature method

NASA Astrophysics Data System (ADS)

Mukherjee, Maharaj; Phan, Vinhthuy

2002-07-01

We describe how to generate better Optical Proximity Corrections (OPC) for line-ends and corners by using rounded anchors and serifs. These rounded serifs and anchors can be made smaller in size and shape than the traditional rectilinear anchors and serifs. The smaller size of the serifs tend to have less problems in satisfying mask-rule constraints. They also have less adverse effects on the printability of neighboring shapes. We refer to these rounded anchors and serifs as Mouse-Ears. The rounding is done by circles which are regular octagons with Ortho-45 straight lines. The main idea of this paper stems from the physical description of the lithographic process, which can be conceptualized as a low-pass filter. The low-pass filter eliminates the sharp corners of the feature which are made of high spatial-frequency components and retains the low spatial-frequency components. Since the rounded anchors and serifs have fewer high-frequency components than their rectilinear counterparts they get less deformed in the lithographic process.

Reduced Reliance on Optimal Facial Information for Identity Recognition in Autism Spectrum Disorder

ERIC Educational Resources Information Center

Leonard, Hayley C.; Annaz, Dagmara; Karmiloff-Smith, Annette; Johnson, Mark H.

2013-01-01

Previous research into face processing in autism spectrum disorder (ASD) has revealed atypical biases toward particular facial information during identity recognition. Specifically, a focus on features (or high spatial frequencies [HSFs]) has been reported for both face and nonface processing in ASD. The current study investigated the development…

Right hemisphere or valence hypothesis, or both? The processing of hybrid faces in the intact and callosotomized brain.

PubMed

Prete, Giulia; Laeng, Bruno; Fabri, Mara; Foschi, Nicoletta; Tommasi, Luca

2015-02-01

The valence hypothesis and the right hemisphere hypothesis in emotion processing have been alternatively supported. To better disentangle the two accounts, we carried out two studies, presenting healthy participants and an anterior callosotomized patient with 'hybrid faces', stimuli created by superimposing the low spatial frequencies of an emotional face to the high spatial frequencies of the same face in a neutral expression. In both studies we asked participants to judge the friendliness level of stimuli, which is an indirect measure of the processing of emotional information, despite this remaining "invisible". In Experiment 1 we presented hybrid faces in a divided visual field paradigm using different tachistoscopic presentation times; in Experiment 2 we presented hybrid chimeric faces in canonical view and upside-down. In Experiments 3 and 4 we tested a callosotomized patient, with spared splenium, in similar paradigms as those used in Experiments 1 and 2. Results from Experiments 1 and 3 were consistent with the valence hypothesis, whereas results of Experiments 2 and 4 were consistent with the right hemisphere hypothesis. This study confirms that the low spatial frequencies of emotional faces influence the social judgments of observers, even when seen for 28 ms (Experiment 1), possibly by means of configural analysis (Experiment 2). The possible roles of the cortical and subcortical emotional routes in these tasks are discussed in the light of the results obtained in the callosotomized patient. We propose that the right hemisphere and the valence accounts are not mutually exclusive, at least in the case of subliminal emotion processing. Copyright © 2015 Elsevier Ltd. All rights reserved.

Sharpening coarse-to-fine stereo vision by perceptual learning: asymmetric transfer across the spatial frequency spectrum

PubMed Central

Tran, Truyet T.; Craven, Ashley P.; Leung, Tsz-Wing; Chat, Sandy W.; Levi, Dennis M.

2016-01-01

Neurons in the early visual cortex are finely tuned to different low-level visual features, forming a multi-channel system analysing the visual image formed on the retina in a parallel manner. However, little is known about the potential ‘cross-talk’ among these channels. Here, we systematically investigated whether stereoacuity, over a large range of target spatial frequencies, can be enhanced by perceptual learning. Using narrow-band visual stimuli, we found that practice with coarse (low spatial frequency) targets substantially improves performance, and that the improvement spreads from coarse to fine (high spatial frequency) three-dimensional perception, generalizing broadly across untrained spatial frequencies and orientations. Notably, we observed an asymmetric transfer of learning across the spatial frequency spectrum. The bandwidth of transfer was broader when training was at a high spatial frequency than at a low spatial frequency. Stereoacuity training is most beneficial when trained with fine targets. This broad transfer of stereoacuity learning contrasts with the highly specific learning reported for other basic visual functions. We also revealed strategies to boost learning outcomes ‘beyond-the-plateau’. Our investigations contribute to understanding the functional properties of the network subserving stereovision. The ability to generalize may provide a key principle for restoring impaired binocular vision in clinical situations. PMID:26909178

The role of spatial attention in visual word processing

NASA Technical Reports Server (NTRS)

Mccann, Robert S.; Folk, Charles L.; Johnston, James C.

1992-01-01

Subjects made lexical decisions on a target letter string presented above or below fixation. In Experiments 1 and 2, target location was cued 100 ms in advance of target onset. Responses were faster on validly than on invalidly cued trials. In Experiment 3, the target was sometimes accompanied by irrelevant stimuli on the other side of fixation; in such cases, responses were slowed (a spatial filtering effect). Both cuing and filtering effects on response time were additive with effects of word frequency and lexical status (words vs. nonwords). These findings are difficult to reconcile with claims that spatial attention is less involved in processing familiar words than in unfamiliar words and nonwords. The results can be reconciled with a late-selection locus of spatial attention only with difficulty, but are easily explained by early-selection models.

Interactions between thalamic and cortical rhythms during semantic memory recall in human

NASA Astrophysics Data System (ADS)

Slotnick, Scott D.; Moo, Lauren R.; Kraut, Michael A.; Lesser, Ronald P.; Hart, John, Jr.

2002-04-01

Human scalp electroencephalographic rhythms, indicative of cortical population synchrony, have long been posited to reflect cognitive processing. Although numerous studies employing simultaneous thalamic and cortical electrode recording in nonhuman animals have explored the role of the thalamus in the modulation of cortical rhythms, direct evidence for thalamocortical modulation in human has not, to our knowledge, been obtained. We simultaneously recorded from thalamic and scalp electrodes in one human during performance of a cognitive task and found a spatially widespread, phase-locked, low-frequency rhythm (7-8 Hz) power decrease at thalamus and scalp during semantic memory recall. This low-frequency rhythm power decrease was followed by a spatially specific, phase-locked, fast-rhythm (21-34 Hz) power increase at thalamus and occipital scalp. Such a pattern of thalamocortical activity reflects a plausible neural mechanism underlying semantic memory recall that may underlie other cognitive processes as well.

[Mechanism underlying spatial vision deficit of monocular amblyopia based on the theory of Magnocellular and Parvocellular (M-P) pathways].

PubMed

Song, Feng-wei; Sun, Zhao-hui; Yang, Yi; Wang, Li-ping; Tang, Xia-jing; Chen, Bin-bin; Yu, Xiao-ning

2014-01-01

To investigate the relationship between the characteristics of spatial vision deficit and the degree of amblyopia in monocular amblyopes, and to analyze its mechanism with the theory of Magnocellular and Parvocellular pathways. One hundred and eleven patients with monocular amblyopes aged 7-34 were included in this study. Distance best corrected visual acuity (BCVA) in logMAR units and contrast sensitivity function test were performed on both eyes in all patients with ETDRS digital visual chart and functional test system OPTECR 6500. The spatial vision of amblyopic and non-amblyopic eyes was evaluated by the AULCSF, Smax, Frmax and cutSF derived from the curve of contrast sensitivity function. The degree of amblyopia was significantly correlated with the difference of AULCSF between the amblyopic and non-amblyopia eyes (r=-0.83, P<0.01). BCVA of amblyopic eyes was significantly correlated with AULCSF, CutSF, Smax, Frmax(r=-0.68, -0.80, -0.73, -0.56, respectively; P<0.01). In amblyopic eyes, significant difference in BCVA, AULCSF, Smax, Frmax and CutSF was seen among different amblyopic groups (P<0.01), which was defined by the degree of amblyopia. In non-amblyopic eyes,no significant difference in BCVA, AULCSF, Smax, Frmax and CutSF was noted among different amblyopic groups (P>0.05). In mild amblyopes, no significant difference in AULCSF and Frmax was found between the amblyopic eyes and non-amblyopic eyes (P>0.05), while Smax and CutSF were significantly different. However, in moderate and severe amblyopes, significant differences in BCVA, AULCSF, Smax, Frmax and CutSF was seen between the amblyopic and non-amblyopic eyes (P<0.01). In amblyopic eyes, significant difference in contrast sensitivity was noted in all kinds of spatial frequencies among different amblyopic groups (P<0.01), and in non-amblyopic eyes, significant differences in contrast sensitivity was not seen in all kinds of spatial frequencies among different amblyopic groups. The AULCSF, CutSF, Smax and Frmax are accorded with visual acuity for evaluation of the spatial vision of amblyopia. As the severity of amblyopia increases, the overall function of spatial vision in amblyopic eyes gradually decreases, the resolution ability of high spatial frequency is gradually weaken, the peak of contrast detection function gradually descends, and the optimal spatial frequency for contrast detection offsets toward low level of spatial frequency. Mild monocular amblyopia produces spatial contrast sensitivity loss in high spatial vision, suggesting there may be decreased sensitivity of the Parvocellular pathway, and no significant anomalous processing of Magnocellular Pathway. Whereas, in moderate and severe amblyopes, a generalized loss of sensitivity is observed at each spatial frequency. This result shows that both Magnocellular and Parvocellular pathways are damaged in different degrees, especially in Parvocellular pathway.

Simultaneous parametric generation and up-conversion of entangled optical images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saygin, M. Yu., E-mail: mihasyu@gmail.com; Chirkin, A. S., E-mail: aschirkin@rambler.r

A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximationmore » for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.« less

Method of and apparatus for thermomagnetically processing a workpiece

DOEpatents

Kisner, Roger A.; Rios, Orlando; Wilgen, John B.; Ludtka, Gerard M.; Ludtka, Gail M.

2014-08-05

A method of thermomagnetically processing a material includes disposing a workpiece within a bore of a magnet; exposing the workpiece to a magnetic field of at least about 1 Tesla generated by the magnet; and, while exposing the workpiece to the magnetic field, applying heat energy to the workpiece at a plurality of frequencies to achieve spatially-controlled heating of the workpiece. An apparatus for thermomagnetically processing a material comprises: a high field strength magnet having a bore extending therethrough for insertion of a workpiece therein; and an energy source disposed adjacent to an entrance to the bore. The energy source is an emitter of variable frequency heat energy, and the bore comprises a waveguide for propagation of the variable frequency heat energy from the energy source to the workpiece.

Continuous-variable quantum computing in optical time-frequency modes using quantum memories.

PubMed

Humphreys, Peter C; Kolthammer, W Steven; Nunn, Joshua; Barbieri, Marco; Datta, Animesh; Walmsley, Ian A

2014-09-26

We develop a scheme for time-frequency encoded continuous-variable cluster-state quantum computing using quantum memories. In particular, we propose a method to produce, manipulate, and measure two-dimensional cluster states in a single spatial mode by exploiting the intrinsic time-frequency selectivity of Raman quantum memories. Time-frequency encoding enables the scheme to be extremely compact, requiring a number of memories that are a linear function of only the number of different frequencies in which the computational state is encoded, independent of its temporal duration. We therefore show that quantum memories can be a powerful component for scalable photonic quantum information processing architectures.

Array processing for RFID tag localization exploiting multi-frequency signals

NASA Astrophysics Data System (ADS)

Zhang, Yimin; Li, Xin; Amin, Moeness G.

2009-05-01

RFID is an increasingly valuable business and technology tool for electronically identifying, locating, and tracking products, assets, and personnel. As a result, precise positioning and tracking of RFID tags and readers have received considerable attention from both academic and industrial communities. Finding the position of RFID tags is considered an important task in various real-time locating systems (RTLS). As such, numerous RFID localization products have been developed for various applications. The majority of RFID positioning systems is based on the fusion of pieces of relevant information, such as the range and the direction-of-arrival (DOA). For example, trilateration can determine the tag position by using the range information of the tag estimated from three or more spatially separated reader antennas. Triangulation is another method to locate RFID tags that use the direction-of-arrival (DOA) information estimated at multiple spatially separated locations. The RFID tag positions can also be determined through hybrid techniques that combine the range and DOA information. The focus of this paper to study the design and performance of the localization of passive RFID tags using array processing techniques in a multipath environment, and exploiting multi-frequency CW signals. The latter are used to decorrelate the coherent multipath signals for effective DOA estimation and for the purpose of accurate range estimation. Accordingly, the spatial and frequency dimensionalities are fully utilized for robust and accurate positioning of RFID tags.

Distinct subsystems for the parafoveal processing of spatial and linguistic information during eye fixations in reading.

PubMed

Inhoff, Albrecht W; Radach, Ralph; Eiter, Brianna M; Juhasz, Barbara

2003-07-01

Two experiments examined readers' use of parafoveally obtained word length information for word recognition. Both experiments manipulated the length (number of constituent characters) of a parafoveally previewed target word so that it was either accurately or inaccurately specified. In Experiment 1, previews also either revealed or denied useful orthographic information. In Experiment 2, parafoveal targets were either high- or low-frequency words. Eye movement contingent display changes were used to show the intact target upon its fixation. Examination of target viewing duration showed completely additive effects of word length previews and of ortho-graphic previews in Experiment 1, viewing duration being shorter in the accurate-length and the orthographic preview conditions. Experiment 2 showed completely additive effects of word length and word frequency, target viewing being shorter in the accurate-length and the high-frequency conditions. Together these results indicate that functionally distinct subsystems control the use of parafoveally visible spatial and linguistic information in reading. Parafoveally visible spatial information appears to be used for two distinct extralinguistic computations: visual object selection and saccade specification.

Vibration-based monitoring and diagnostics using compressive sensing

NASA Astrophysics Data System (ADS)

Ganesan, Vaahini; Das, Tuhin; Rahnavard, Nazanin; Kauffman, Jeffrey L.

2017-04-01

Vibration data from mechanical systems carry important information that is useful for characterization and diagnosis. Standard approaches rely on continually streaming data at a fixed sampling frequency. For applications involving continuous monitoring, such as Structural Health Monitoring (SHM), such approaches result in high volume data and rely on sensors being powered for prolonged durations. Furthermore, for spatial resolution, structures are instrumented with a large array of sensors. This paper shows that both volume of data and number of sensors can be reduced significantly by applying Compressive Sensing (CS) in vibration monitoring applications. The reduction is achieved by using random sampling and capitalizing on the sparsity of vibration signals in the frequency domain. Preliminary experimental results validating CS-based frequency recovery are also provided. By exploiting the sparsity of mode shapes, CS can also enable efficient spatial reconstruction using fewer spatially distributed sensors. CS can thereby reduce the cost and power requirement of sensing as well as streamline data storage and processing in monitoring applications. In well-instrumented structures, CS can enable continued monitoring in case of sensor or computational failures.

Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben

2016-04-11

The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350–400 nm tall and ∼90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

The functional significance of velocity storage and its dependence on gravity.

PubMed

Laurens, Jean; Angelaki, Dora E

2011-05-01

Research in the vestibular field has revealed the existence of a central process, called 'velocity storage', that is activated by both visual and vestibular rotation cues and is modified by gravity, but whose functional relevance during natural motion has often been questioned. In this review, we explore spatial orientation in the context of a Bayesian model of vestibular information processing. In this framework, deficiencies/ambiguities in the peripheral vestibular sensors are compensated for by central processing to more accurately estimate rotation velocity, orientation relative to gravity, and inertial motion. First, an inverse model of semicircular canal dynamics is used to reconstruct rotation velocity by integrating canal signals over time. However, its low-frequency bandwidth is limited to avoid accumulation of noise in the integrator. A second internal model uses this reconstructed rotation velocity to compute an internal estimate of tilt and inertial acceleration. The bandwidth of this second internal model is also restricted at low frequencies to avoid noise accumulation and drift of the tilt/translation estimator over time. As a result, low-frequency translation can be erroneously misinterpreted as tilt. The time constants of these two integrators (internal models) can be conceptualized as two Bayesian priors of zero rotation velocity and zero linear acceleration, respectively. The model replicates empirical observations like 'velocity storage' and 'frequency segregation' and explains spatial orientation (e.g., 'somatogravic') illusions. Importantly, the functional significance of this network, including velocity storage, is found during short-lasting, natural head movements, rather than at low frequencies with which it has been traditionally studied.

The functional significance of velocity storage and its dependence on gravity

PubMed Central

Laurens, Jean

2013-01-01

Research in the vestibular field has revealed the existence of a central process, called ‘velocity storage’, that is activated by both visual and vestibular rotation cues and is modified by gravity, but whose functional relevance during natural motion has often been questioned. In this review, we explore spatial orientation in the context of a Bayesian model of vestibular information processing. In this framework, deficiencies/ambiguities in the peripheral vestibular sensors are compensated for by central processing to more accurately estimate rotation velocity, orientation relative to gravity, and inertial motion. First, an inverse model of semicircular canal dynamics is used to reconstruct rotation velocity by integrating canal signals over time. However, its low-frequency bandwidth is limited to avoid accumulation of noise in the integrator. A second internal model uses this reconstructed rotation velocity to compute an internal estimate of tilt and inertial acceleration. The bandwidth of this second internal model is also restricted at low frequencies to avoid noise accumulation and drift of the tilt/translation estimator over time. As a result, low-frequency translation can be erroneously misinterpreted as tilt. The time constants of these two integrators (internal models) can be conceptualized as two Bayesian priors of zero rotation velocity and zero linear acceleration, respectively. The model replicates empirical observations like ‘velocity storage’ and ‘frequency segregation’ and explains spatial orientation (e.g., ‘somatogravic’) illusions. Importantly, the functional significance of this network, including velocity storage, is found during short-lasting, natural head movements, rather than at low frequencies with which it has been traditionally studied. PMID:21293850

Processing of Fear and Anger Facial Expressions: The Role of Spatial Frequency

PubMed Central

Comfort, William E.; Wang, Meng; Benton, Christopher P.; Zana, Yossi

2013-01-01

Spatial frequency (SF) components encode a portion of the affective value expressed in face images. The aim of this study was to estimate the relative weight of specific frequency spectrum bandwidth on the discrimination of anger and fear facial expressions. The general paradigm was a classification of the expression of faces morphed at varying proportions between anger and fear images in which SF adaptation and SF subtraction are expected to shift classification of facial emotion. A series of three experiments was conducted. In Experiment 1 subjects classified morphed face images that were unfiltered or filtered to remove either low (<8 cycles/face), middle (12–28 cycles/face), or high (>32 cycles/face) SF components. In Experiment 2 subjects were adapted to unfiltered or filtered prototypical (non-morphed) fear face images and subsequently classified morphed face images. In Experiment 3 subjects were adapted to unfiltered or filtered prototypical fear face images with the phase component randomized before classifying morphed face images. Removing mid frequency components from the target images shifted classification toward fear. The same shift was observed under adaptation condition to unfiltered and low- and middle-range filtered fear images. However, when the phase spectrum of the same adaptation stimuli was randomized, no adaptation effect was observed. These results suggest that medium SF components support the perception of fear more than anger at both low and high level of processing. They also suggest that the effect at high-level processing stage is related more to high-level featural and/or configural information than to the low-level frequency spectrum. PMID:23637687

Generation of laser-induced periodic surface structures on transparent material-fused silica

NASA Astrophysics Data System (ADS)

Schwarz, Simon; Rung, Stefan; Hellmann, Ralf

2016-05-01

We report on a comparison between simulated and experimental results for the generation of laser-induced periodic surface structures with low spatial frequency on dielectrics. Using the established efficacy factor theory extended by a Drude model, we determine the required carrier density for the generation of low spatial frequency LIPSS (LSFL) and forecast their periodicity and orientation. In a subsequent calculative step, we determine the fluence of ultrashort laser pulses necessary to excite this required carrier density in due consideration of the pulse number dependent ablation threshold. The later calculation is based on a rate equation including photo- and avalanche ionization and derives appropriate process parameters for a selective generation of LSFL. Exemplarily, we apply this approach to the generation of LSFL on fused silica using a 1030 nm femtosecond laser. The experimental results for the orientation and spatial periodicity of LSFL reveal excellent agreement with the simulation.

Generation of laser-induced periodic surface structures on transparent material-fused silica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarz, Simon; Rung, Stefan; Hellmann, Ralf

2016-05-02

We report on a comparison between simulated and experimental results for the generation of laser-induced periodic surface structures with low spatial frequency on dielectrics. Using the established efficacy factor theory extended by a Drude model, we determine the required carrier density for the generation of low spatial frequency LIPSS (LSFL) and forecast their periodicity and orientation. In a subsequent calculative step, we determine the fluence of ultrashort laser pulses necessary to excite this required carrier density in due consideration of the pulse number dependent ablation threshold. The later calculation is based on a rate equation including photo- and avalanche ionizationmore » and derives appropriate process parameters for a selective generation of LSFL. Exemplarily, we apply this approach to the generation of LSFL on fused silica using a 1030 nm femtosecond laser. The experimental results for the orientation and spatial periodicity of LSFL reveal excellent agreement with the simulation.« less

The NIST Real-Time Control System (RCS): A Reference Model Architecture for Computational Intelligence

NASA Technical Reports Server (NTRS)

Albus, James S.

1996-01-01

The Real-time Control System (RCS) developed at NIST and elsewhere over the past two decades defines a reference model architecture for design and analysis of complex intelligent control systems. The RCS architecture consists of a hierarchically layered set of functional processing modules connected by a network of communication pathways. The primary distinguishing feature of the layers is the bandwidth of the control loops. The characteristic bandwidth of each level is determined by the spatial and temporal integration window of filters, the temporal frequency of signals and events, the spatial frequency of patterns, and the planning horizon and granularity of the planners that operate at each level. At each level, tasks are decomposed into sequential subtasks, to be performed by cooperating sets of subordinate agents. At each level, signals from sensors are filtered and correlated with spatial and temporal features that are relevant to the control function being implemented at that level.

Task-induced frequency modulation features for brain-computer interfacing.

PubMed

Jayaram, Vinay; Hohmann, Matthias; Just, Jennifer; Schölkopf, Bernhard; Grosse-Wentrup, Moritz

2017-10-01

Task-induced amplitude modulation of neural oscillations is routinely used in brain-computer interfaces (BCIs) for decoding subjects' intents, and underlies some of the most robust and common methods in the field, such as common spatial patterns and Riemannian geometry. While there has been some interest in phase-related features for classification, both techniques usually presuppose that the frequencies of neural oscillations remain stable across various tasks. We investigate here whether features based on task-induced modulation of the frequency of neural oscillations enable decoding of subjects' intents with an accuracy comparable to task-induced amplitude modulation. We compare cross-validated classification accuracies using the amplitude and frequency modulated features, as well as a joint feature space, across subjects in various paradigms and pre-processing conditions. We show results with a motor imagery task, a cognitive task, and also preliminary results in patients with amyotrophic lateral sclerosis (ALS), as well as using common spatial patterns and Laplacian filtering. The frequency features alone do not significantly out-perform traditional amplitude modulation features, and in some cases perform significantly worse. However, across both tasks and pre-processing in healthy subjects the joint space significantly out-performs either the frequency or amplitude features alone. This result only does not hold for ALS patients, for whom the dataset is of insufficient size to draw any statistically significant conclusions. Task-induced frequency modulation is robust and straight forward to compute, and increases performance when added to standard amplitude modulation features across paradigms. This allows more information to be extracted from the EEG signal cheaply and can be used throughout the field of BCIs.

Feedback and feedforward control of frequency tuning to naturalistic stimuli.

PubMed

Chacron, Maurice J; Maler, Leonard; Bastian, Joseph

2005-06-08

Sensory neurons must respond to a wide variety of natural stimuli that can have very different spatiotemporal characteristics. Optimal responsiveness to subsets of these stimuli can be achieved by devoting specialized neural circuitry to different stimulus categories, or, alternatively, this circuitry can be modulated or tuned to optimize responsiveness to current stimulus conditions. This study explores the mechanisms that enable neurons within the initial processing station of the electrosensory system of weakly electric fish to shift their tuning properties based on the spatial extent of the stimulus. These neurons are tuned to low frequencies when the stimulus is restricted to a small region within the receptive field center but are tuned to higher frequencies when the stimulus impinges on large regions of the sensory epithelium. Through a combination of modeling and in vivo electrophysiology, we reveal the respective contributions of the filtering characteristics of extended dendritic structures and feedback circuitry to this shift in tuning. Our results show that low-frequency tuning can result from the cable properties of an extended dendrite that conveys receptor-afferent information to the cell body. The shift from low- to high-frequency tuning, seen in response to spatially extensive stimuli, results from increased wide-band input attributable to activation of larger populations of receptor afferents, as well as the activation of parallel fiber feedback from the cerebellum. This feedback provides a cancellation signal with low-pass characteristics that selectively attenuates low-frequency responsiveness. Thus, with spatially extensive stimuli, these cells preferentially respond to the higher-frequency components of the receptor-afferent input.

An integrated analysis-synthesis array system for spatial sound fields.

PubMed

Bai, Mingsian R; Hua, Yi-Hsin; Kuo, Chia-Hao; Hsieh, Yu-Hao

2015-03-01

An integrated recording and reproduction array system for spatial audio is presented within a generic framework akin to the analysis-synthesis filterbanks in discrete time signal processing. In the analysis stage, a microphone array "encodes" the sound field by using the plane-wave decomposition. Direction of arrival of plane-wave components that comprise the sound field of interest are estimated by multiple signal classification. Next, the source signals are extracted by using a deconvolution procedure. In the synthesis stage, a loudspeaker array "decodes" the sound field by reconstructing the plane-wave components obtained in the analysis stage. This synthesis stage is carried out by pressure matching in the interior domain of the loudspeaker array. The deconvolution problem is solved by truncated singular value decomposition or convex optimization algorithms. For high-frequency reproduction that suffers from the spatial aliasing problem, vector panning is utilized. Listening tests are undertaken to evaluate the deconvolution method, vector panning, and a hybrid approach that combines both methods to cover frequency ranges below and above the spatial aliasing frequency. Localization and timbral attributes are considered in the subjective evaluation. The results show that the hybrid approach performs the best in overall preference. In addition, there is a trade-off between reproduction performance and the external radiation.

Space-Time Processing for Tactical Mobile Ad Hoc Networks

DTIC Science & Technology

2010-05-01

Spatial Diversity and Imperfect Channel Estimation on Wideband MC- DS - CDMA and MC- CDMA " IEEE Transactions on Communications, Vol. 57, No. 10, pp. 2988...include direct sequence code division multiple access ( DS - CDMA ), Frequency Hopped (FH) CDMA and Orthogonal Frequency Division Multiple Access (OFDMA...capability, LPD/LPI, and operability in non-continuous spectrum. In addition, FH- CDMA is robust to the near-far problem, while DS - CDMA requires

Model of human visual-motion sensing

NASA Technical Reports Server (NTRS)

Watson, A. B.; Ahumada, A. J., Jr.

1985-01-01

A model of how humans sense the velocity of moving images is proposed. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

Spatial Frequency and Face Processing in Children with Autism and Asperger Syndrome

ERIC Educational Resources Information Center

Deruelle, Christine; Rondan, Cecilie; Gepner, Bruno; Tardif, Carole

2004-01-01

Two experiments were designed to investigate possible abnormal face processing strategies in children with autistic spectrum disorders. A group of 11 children with autism was compared to two groups of normally developing children matched on verbal mental age and on chronological age. In the first experiment, participants had to recognize faces on…

Spectrum Control through Discrete Frequency Diffraction in the Presence of Photonic Gauge Potentials

NASA Astrophysics Data System (ADS)

Qin, Chengzhi; Zhou, Feng; Peng, Yugui; Sounas, Dimitrios; Zhu, Xuefeng; Wang, Bing; Dong, Jianji; Zhang, Xinliang; Alù; , Andrea; Lu, Peixiang

2018-03-01

By using optical phase modulators in a fiber-optical circuit, we theoretically and experimentally demonstrate large control over the spectrum of an impinging signal, which may evolve analogously to discrete diffraction in spatial waveguide arrays. The modulation phase acts as a photonic gauge potential in the frequency dimension, realizing efficient control of the central frequency and bandwidth of frequency combs. We experimentally achieve a 50 GHz frequency shift and threefold bandwidth expansion of an impinging comb, as well as the frequency analogue of various refraction phenomena, including negative refraction and perfect focusing in the frequency domain, both for discrete and continuous incident spectra. Our study paves a promising way towards versatile frequency management for optical communications and signal processing using time modulation schemes.

A small terminal for satellite communication systems

NASA Technical Reports Server (NTRS)

Xiong, Fuqin; Wu, Dong; Jin, Min

1994-01-01

A small portable, low-cost satellite communications terminal system incorporating a modulator/demodulator and convolutional-Viterbi coder/decoder is described. Advances in signal processing and error-correction techniques in combination with higher power and higher frequencies aboard satellites allow for more efficient use of the space segment. This makes it possible to design small economical earth stations. The Advanced Communications Technology Satellite (ACTS) was chosen to test the system. ACTS, operating at the Ka band incorporates higher power, higher frequency, frequency and spatial reuse using spot beams and polarization.

Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions

PubMed Central

Bradley, Arthur; Xu, Renfeng; Thibos, Larry; Marin, Gildas; Hernandez, Martha

2014-01-01

Purpose To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration. Methods Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using “darker” and “sharper” subjective criteria. Results Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1 to 1.5 mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the “darker” or “sharper” subjective criteria bias the patient to use lower or higher spatial frequencies respectively. Conclusions In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a “sharper” criterion during subjective refractions will improve image quality for high spatial frequencies and generate pupil size independent refractions. PMID:24397356

Pattern masking: the importance of remote spatial frequencies and their phase alignment.

PubMed

Huang, Pi-Chun; Maehara, Goro; May, Keith A; Hess, Robert F

2012-02-16

To assess the effects of spatial frequency and phase alignment of mask components in pattern masking, target threshold vs. mask contrast (TvC) functions for a sine-wave grating (S) target were measured for five types of mask: a sine-wave grating (S), a square-wave grating (Q), a missing fundamental square-wave grating (M), harmonic complexes consisting of phase-scrambled harmonics of a square wave (Qp), and harmonic complexes consisting of phase-scrambled harmonics of a missing fundamental square wave (Mp). Target and masks had the same fundamental frequency (0.46 cpd) and the target was added in phase with the fundamental frequency component of the mask. Under monocular viewing conditions, the strength of masking depends on phase relationships among mask spatial frequencies far removed from that of the target, at least 3 times the target frequency, only when there are common target and mask spatial frequencies. Under dichoptic viewing conditions, S and Q masks produced similar masking to each other and the phase-scrambled masks (Qp and Mp) produced less masking. The results suggest that pattern masking is spatial frequency broadband in nature and sensitive to the phase alignments of spatial components.

Influence of 4,4’-azobis (4-cyanopentanoic acid) in Transmission and Reflection Gratings Stored in a PVA/AA Photopolymer

PubMed Central

Fernandez, Elena; Fuentes, Rosa; Belendez, Augusto; Pascual, Inmaculada

2016-01-01

Holographic transmission gratings with a spatial frequency of 2658 lines/mm and reflection gratings with a spatial frequency of 4553 lines/mm were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) based photopolymer. This material can reach diffraction efficiencies close to 100% for spatial frequencies about 1000 lines/mm. However, for higher spatial frequencies, the diffraction efficiency decreases considerably as the spatial frequency increases. To enhance the material response at high spatial frequencies, a chain transfer agent, the 4,4’-azobis (4-cyanopentanoic acid), ACPA, is added to the composition of the material. Different concentrations of ACPA are incorporated into the main composition of the photopolymer to find the concentration value that provides the highest diffraction efficiency. Moreover, the refractive index modulation and the optical thickness of the transmission and reflection gratings were obtained, evaluated and compared to procure more information about the influence of the ACPA on them. PMID:28773322

3-D vision and figure-ground separation by visual cortex.

PubMed

Grossberg, S

1994-01-01

A neural network theory of three-dimensional (3-D) vision, called FACADE theory, is described. The theory proposes a solution of the classical figure-ground problem for biological vision. It does so by suggesting how boundary representations and surface representations are formed within a boundary contour system (BCS) and a feature contour system (FCS). The BCS and FCS interact reciprocally to form 3-D boundary and surface representations that are mutually consistent. Their interactions generate 3-D percepts wherein occluding and occluded object parts are separated, completed, and grouped. The theory clarifies how preattentive processes of 3-D perception and figure-ground separation interact reciprocally with attentive processes of spatial localization, object recognition, and visual search. A new theory of stereopsis is proposed that predicts how cells sensitive to multiple spatial frequencies, disparities, and orientations are combined by context-sensitive filtering, competition, and cooperation to form coherent BCS boundary segmentations. Several factors contribute to figure-ground pop-out, including: boundary contrast between spatially contiguous boundaries, whether due to scenic differences in luminance, color, spatial frequency, or disparity; partially ordered interactions from larger spatial scales and disparities to smaller scales and disparities; and surface filling-in restricted to regions surrounded by a connected boundary. Phenomena such as 3-D pop-out from a 2-D picture, Da Vinci stereopsis, 3-D neon color spreading, completion of partially occluded objects, and figure-ground reversals are analyzed. The BCS and FCS subsystems model aspects of how the two parvocellular cortical processing streams that join the lateral geniculate nucleus to prestriate cortical area V4 interact to generate a multiplexed representation of Form-And-Color-And-DEpth, or FACADE, within area V4. Area V4 is suggested to support figure-ground separation and to interact with cortical mechanisms of spatial attention, attentive object learning, and visual search. Adaptive resonance theory (ART) mechanisms model aspects of how prestriate visual cortex interacts reciprocally with a visual object recognition system in inferotemporal (IT) cortex for purposes of attentive object learning and categorization. Object attention mechanisms of the What cortical processing stream through IT cortex are distinguished from spatial attention mechanisms of the Where cortical processing stream through parietal cortex. Parvocellular BCS and FCS signals interact with the model What stream. Parvocellular FCS and magnocellular motion BCS signals interact with the model Where stream.(ABSTRACT TRUNCATED AT 400 WORDS)

Separate channels for the analysis of the shape and the movement of moving visual stimulus.

PubMed

Tolhurst, D J

1973-06-01

1. The effects of temporal modulation on the properties of spatial frequency channels have been investigated using adaptation.2. Adapting to drifting sinusoidal gratings caused threshold elevation that was both spatial frequency and direction specific. Little systematic difference was found between the band widths of the elevation curves for drifting and stationary gratings.3. It was confirmed that adaptation fails to reveal channels at low spatial frequencies when stationary gratings are used. However, channels were revealed at frequencies at least as low as 0.66 c/deg when the test gratings were made to move. These channels are adapted only a little by stationary gratings, confirming their dependence on movement.4. The existence of movement-sensitive channels at low spatial frequencies explains the well known observation that temporal modulation greatly increases the sensitivity of the visual system to low spatial frequencies.5. Temporal modulation was effective at revealing these channels only when the flicker or movement of the test patterns was apparent to the observer; only at low spatial frequencies did patterns, modulated at low rates, actually appear to be temporarily modulated at threshold. At higher spatial frequencies, they were indistinguishable from stationary patterns until the contrast was some way above the detection threshold.6. It is suggested, therefore, that the movement-sensitive channels are responsible for signalling the occurrence of movement; the channels at higher spatial frequencies give no information about temporal changes. These two systems of channels are compared to the Y- and X-cells respectively of the cat.

Attention to local and global levels of hierarchical Navon figures affects rapid scene categorization.

PubMed

Brand, John; Johnson, Aaron P

2014-01-01

In four experiments, we investigated how attention to local and global levels of hierarchical Navon figures affected the selection of diagnostic spatial scale information used in scene categorization. We explored this issue by asking observers to classify hybrid images (i.e., images that contain low spatial frequency (LSF) content of one image, and high spatial frequency (HSF) content from a second image) immediately following global and local Navon tasks. Hybrid images can be classified according to either their LSF, or HSF content; thus, making them ideal for investigating diagnostic spatial scale preference. Although observers were sensitive to both spatial scales (Experiment 1), they overwhelmingly preferred to classify hybrids based on LSF content (Experiment 2). In Experiment 3, we demonstrated that LSF based hybrid categorization was faster following global Navon tasks, suggesting that LSF processing associated with global Navon tasks primed the selection of LSFs in hybrid images. In Experiment 4, replicating Experiment 3 but suppressing the LSF information in Navon letters by contrast balancing the stimuli examined this hypothesis. Similar to Experiment 3, observers preferred to classify hybrids based on LSF content; however and in contrast, LSF based hybrid categorization was slower following global than local Navon tasks.

What spatial scales are believable for climate model projections of sea surface temperature?

NASA Astrophysics Data System (ADS)

Kwiatkowski, Lester; Halloran, Paul R.; Mumby, Peter J.; Stephenson, David B.

2014-09-01

Earth system models (ESMs) provide high resolution simulations of variables such as sea surface temperature (SST) that are often used in off-line biological impact models. Coral reef modellers have used such model outputs extensively to project both regional and global changes to coral growth and bleaching frequency. We assess model skill at capturing sub-regional climatologies and patterns of historical warming. This study uses an established wavelet-based spatial comparison technique to assess the skill of the coupled model intercomparison project phase 5 models to capture spatial SST patterns in coral regions. We show that models typically have medium to high skill at capturing climatological spatial patterns of SSTs within key coral regions, with model skill typically improving at larger spatial scales (≥4°). However models have much lower skill at modelling historical warming patters and are shown to often perform no better than chance at regional scales (e.g. Southeast Asian) and worse than chance at finer scales (<8°). Our findings suggest that output from current generation ESMs is not yet suitable for making sub-regional projections of change in coral bleaching frequency and other marine processes linked to SST warming.

Attention to local and global levels of hierarchical Navon figures affects rapid scene categorization

PubMed Central

Brand, John; Johnson, Aaron P.

2014-01-01

In four experiments, we investigated how attention to local and global levels of hierarchical Navon figures affected the selection of diagnostic spatial scale information used in scene categorization. We explored this issue by asking observers to classify hybrid images (i.e., images that contain low spatial frequency (LSF) content of one image, and high spatial frequency (HSF) content from a second image) immediately following global and local Navon tasks. Hybrid images can be classified according to either their LSF, or HSF content; thus, making them ideal for investigating diagnostic spatial scale preference. Although observers were sensitive to both spatial scales (Experiment 1), they overwhelmingly preferred to classify hybrids based on LSF content (Experiment 2). In Experiment 3, we demonstrated that LSF based hybrid categorization was faster following global Navon tasks, suggesting that LSF processing associated with global Navon tasks primed the selection of LSFs in hybrid images. In Experiment 4, replicating Experiment 3 but suppressing the LSF information in Navon letters by contrast balancing the stimuli examined this hypothesis. Similar to Experiment 3, observers preferred to classify hybrids based on LSF content; however and in contrast, LSF based hybrid categorization was slower following global than local Navon tasks. PMID:25520675

Restricted spatial regression in practice: Geostatistical models, confounding, and robustness under model misspecification

USGS Publications Warehouse

Hanks, Ephraim M.; Schliep, Erin M.; Hooten, Mevin B.; Hoeting, Jennifer A.

2015-01-01

In spatial generalized linear mixed models (SGLMMs), covariates that are spatially smooth are often collinear with spatially smooth random effects. This phenomenon is known as spatial confounding and has been studied primarily in the case where the spatial support of the process being studied is discrete (e.g., areal spatial data). In this case, the most common approach suggested is restricted spatial regression (RSR) in which the spatial random effects are constrained to be orthogonal to the fixed effects. We consider spatial confounding and RSR in the geostatistical (continuous spatial support) setting. We show that RSR provides computational benefits relative to the confounded SGLMM, but that Bayesian credible intervals under RSR can be inappropriately narrow under model misspecification. We propose a posterior predictive approach to alleviating this potential problem and discuss the appropriateness of RSR in a variety of situations. We illustrate RSR and SGLMM approaches through simulation studies and an analysis of malaria frequencies in The Gambia, Africa.

Discriminative spatial-frequency-temporal feature extraction and classification of motor imagery EEG: An sparse regression and Weighted Naïve Bayesian Classifier-based approach.

PubMed

Miao, Minmin; Zeng, Hong; Wang, Aimin; Zhao, Changsen; Liu, Feixiang

2017-02-15

Common spatial pattern (CSP) is most widely used in motor imagery based brain-computer interface (BCI) systems. In conventional CSP algorithm, pairs of the eigenvectors corresponding to both extreme eigenvalues are selected to construct the optimal spatial filter. In addition, an appropriate selection of subject-specific time segments and frequency bands plays an important role in its successful application. This study proposes to optimize spatial-frequency-temporal patterns for discriminative feature extraction. Spatial optimization is implemented by channel selection and finding discriminative spatial filters adaptively on each time-frequency segment. A novel Discernibility of Feature Sets (DFS) criteria is designed for spatial filter optimization. Besides, discriminative features located in multiple time-frequency segments are selected automatically by the proposed sparse time-frequency segment common spatial pattern (STFSCSP) method which exploits sparse regression for significant features selection. Finally, a weight determined by the sparse coefficient is assigned for each selected CSP feature and we propose a Weighted Naïve Bayesian Classifier (WNBC) for classification. Experimental results on two public EEG datasets demonstrate that optimizing spatial-frequency-temporal patterns in a data-driven manner for discriminative feature extraction greatly improves the classification performance. The proposed method gives significantly better classification accuracies in comparison with several competing methods in the literature. The proposed approach is a promising candidate for future BCI systems. Copyright © 2016 Elsevier B.V. All rights reserved.

T-phase and tsunami signals recorded by IMS hydrophone triplets during the 2011 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Matsumoto, H.; Haralabus, G.; Zampolli, M.; Ozel, N. M.; Yamada, T.; Mark, P. K.

2016-12-01

A hydrophone station of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is used to estimate the back-azimuth of T-phase signals generated by the 2011 Tohoku earthquake. Among the 6 IMS hydrophone stations required by the Treaty, 5 stations consist of two triplets, with the exception of HA1 (Australia), which has only one. The hydrophones of each triplet are suspended in the SOFAR channel and arranged to form an equilateral triangle with each side being approximately two kilometers long. The waveforms from the Tohoku earthquake were received at HA11, located on Wake Island, which is located approximately 3100 km south-east of the earthquake epicenter. The frequency range used in the array analysis was chosen to be less than 0.375 Hz, which assumed the target phase velocity to be 1.5 km/s for T-phases. The T-phase signals that originated from the seismic source however show peaks in the frequency band above one Hz. As a result of the inter-element distances of 2 km, spatial aliasing is observed in the frequency-wavenumber analysis (F-K analysis) if the entire 100 Hz bandwidth of the hydrophones is used. This spatial aliasing is significant because the distance between hydrophones in the triplet is large in comparison to the ratio between the phase velocity of T-phase signals and the frequency. To circumvent this spatial aliasing problem, a three-step processing technique used in seismic array analysis is applied: (1) high-pass filtering above 1 Hz to retrieve the T-phase, followed by (2) extraction of the envelope of this signal to highlight the T-phase contribution, and finally (3) low-pass filtering of the envelope below 0.375 Hz. The F-K analysis provides accurate back-azimuth and slowness estimations without spatial aliasing. Deconvolved waveforms are also processed to retrieve tsunami components by using a three-pole model of the frequency-amplitude-phase (FAP) response below 0.1 Hz and the measured sensor response for higher frequencies. It is also shown that short-period pressure fluctuations recorded by the IMS hydrophones correspond to theoretical dispersion curves of tsunamis. Thus, short-period dispersive tsunami signals can be identified by the IMS hydrophone triplets.

Spectral analysis and filtering techniques in digital spatial data processing

USGS Publications Warehouse

Pan, Jeng-Jong

1989-01-01

A filter toolbox has been developed at the EROS Data Center, US Geological Survey, for retrieving or removing specified frequency information from two-dimensional digital spatial data. This filter toolbox provides capabilities to compute the power spectrum of a given data and to design various filters in the frequency domain. Three types of filters are available in the toolbox: point filter, line filter, and area filter. Both the point and line filters employ Gaussian-type notch filters, and the area filter includes the capabilities to perform high-pass, band-pass, low-pass, and wedge filtering techniques. These filters are applied for analyzing satellite multispectral scanner data, airborne visible and infrared imaging spectrometer (AVIRIS) data, gravity data, and the digital elevation models (DEM) data. -from Author

Controlling Energy Radiations of Electromagnetic Waves via Frequency Coding Metamaterials.

PubMed

Wu, Haotian; Liu, Shuo; Wan, Xiang; Zhang, Lei; Wang, Dan; Li, Lianlin; Cui, Tie Jun

2017-09-01

Metamaterials are artificial structures composed of subwavelength unit cells to control electromagnetic (EM) waves. The spatial coding representation of metamaterial has the ability to describe the material in a digital way. The spatial coding metamaterials are typically constructed by unit cells that have similar shapes with fixed functionality. Here, the concept of frequency coding metamaterial is proposed, which achieves different controls of EM energy radiations with a fixed spatial coding pattern when the frequency changes. In this case, not only different phase responses of the unit cells are considered, but also different phase sensitivities are also required. Due to different frequency sensitivities of unit cells, two units with the same phase response at the initial frequency may have different phase responses at higher frequency. To describe the frequency coding property of unit cell, digitalized frequency sensitivity is proposed, in which the units are encoded with digits "0" and "1" to represent the low and high phase sensitivities, respectively. By this merit, two degrees of freedom, spatial coding and frequency coding, are obtained to control the EM energy radiations by a new class of frequency-spatial coding metamaterials. The above concepts and physical phenomena are confirmed by numerical simulations and experiments.

Design Considerations of Polishing Lap for Computer-Controlled Cylindrical Polishing Process

NASA Technical Reports Server (NTRS)

Khan, Gufran S.; Gubarev, Mikhail; Speegle, Chet; Ramsey, Brian

2010-01-01

The future X-ray observatory missions, such as International X-ray Observatory, require grazing incidence replicated optics of extremely large collecting area (3 m2) in combination with angular resolution of less than 5 arcsec half-power diameter. The resolution of a mirror shell depends ultimately on the quality of the cylindrical mandrels from which they are being replicated. Mid-spatial-frequency axial figure error is a dominant contributor in the error budget of the mandrel. This paper presents our efforts to develop a deterministic cylindrical polishing process in order to keep the mid-spatial-frequency axial figure errors to a minimum. Simulation studies have been performed to optimize the operational parameters as well as the polishing lap configuration. Furthermore, depending upon the surface error profile, a model for localized polishing based on dwell time approach is developed. Using the inputs from the mathematical model, a mandrel, having conical approximated Wolter-1 geometry, has been polished on a newly developed computer-controlled cylindrical polishing machine. We report our first experimental results and discuss plans for further improvements in the polishing process.

Investigation of KDP crystal surface based on an improved bidimensional empirical mode decomposition method

NASA Astrophysics Data System (ADS)

Lu, Lei; Yan, Jihong; Chen, Wanqun; An, Shi

2018-03-01

This paper proposed a novel spatial frequency analysis method for the investigation of potassium dihydrogen phosphate (KDP) crystal surface based on an improved bidimensional empirical mode decomposition (BEMD) method. Aiming to eliminate end effects of the BEMD method and improve the intrinsic mode functions (IMFs) for the efficient identification of texture features, a denoising process was embedded in the sifting iteration of BEMD method. With removing redundant information in decomposed sub-components of KDP crystal surface, middle spatial frequencies of the cutting and feeding processes were identified. Comparative study with the power spectral density method, two-dimensional wavelet transform (2D-WT), as well as the traditional BEMD method, demonstrated that the method developed in this paper can efficiently extract texture features and reveal gradient development of KDP crystal surface. Furthermore, the proposed method was a self-adaptive data driven technique without prior knowledge, which overcame shortcomings of the 2D-WT model such as the parameters selection. Additionally, the proposed method was a promising tool for the application of online monitoring and optimal control of precision machining process.

Speech reception with different bilateral directional processing schemes: Influence of binaural hearing, audiometric asymmetry, and acoustic scenario.

PubMed

Neher, Tobias; Wagener, Kirsten C; Latzel, Matthias

2017-09-01

Hearing aid (HA) users can differ markedly in their benefit from directional processing (or beamforming) algorithms. The current study therefore investigated candidacy for different bilateral directional processing schemes. Groups of elderly listeners with symmetric (N = 20) or asymmetric (N = 19) hearing thresholds for frequencies below 2 kHz, a large spread in the binaural intelligibility level difference (BILD), and no difference in age, overall degree of hearing loss, or performance on a measure of selective attention took part. Aided speech reception was measured using virtual acoustics together with a simulation of a linked pair of completely occluding behind-the-ear HAs. Five processing schemes and three acoustic scenarios were used. The processing schemes differed in the tradeoff between signal-to-noise ratio (SNR) improvement and binaural cue preservation. The acoustic scenarios consisted of a frontal target talker presented against two speech maskers from ±60° azimuth or spatially diffuse cafeteria noise. For both groups, a significant interaction between BILD, processing scheme, and acoustic scenario was found. This interaction implied that, in situations with lateral speech maskers, HA users with BILDs larger than about 2 dB profited more from preserved low-frequency binaural cues than from greater SNR improvement, whereas for smaller BILDs the opposite was true. Audiometric asymmetry reduced the influence of binaural hearing. In spatially diffuse noise, the maximal SNR improvement was generally beneficial. N 0 S π detection performance at 500 Hz predicted the benefit from low-frequency binaural cues. Together, these findings provide a basis for adapting bilateral directional processing to individual and situational influences. Further research is needed to investigate their generalizability to more realistic HA conditions (e.g., with low-frequency vent-transmitted sound). Copyright © 2017 Elsevier B.V. All rights reserved.

Compressive Channel Estimation and Tracking for Large Arrays in mm Wave Picocells

DTIC Science & Technology

2014-01-01

abling sophisticated adaptation, including frequency-selective spatiotemporal processing (e.g., per subcarrier beamforming in OFDM systems). This approach...subarrays are certainly required for more advanced functionalities such as multiuser MIMO [17], spatial multiplexing [18], [19], [20], [21], [22], and...case, a regu- larly spaced 2D array), an estimate of the N2t,1D × N2r,1D MIMO channel matrix H can be efficiently arrived at by estimating the spatial

Broadband interferometric characterization of divergence and spatial chirp.

PubMed

Meier, Amanda K; Iliev, Marin; Squier, Jeff A; Durfee, Charles G

2015-09-01

We demonstrate a spectral interferometric method to characterize lateral and angular spatial chirp to optimize intensity localization in spatio-temporally focused ultrafast beams. Interference between two spatially sheared beams in an interferometer will lead to straight fringes if the wavefronts are curved. To produce reference fringes, we delay one arm relative to another in order to measure fringe rotation in the spatially resolved spectral interferogram. With Fourier analysis, we can obtain frequency-resolved divergence. In another arrangement, we spatially flip one beam relative to the other, which allows the frequency-dependent beamlet direction (angular spatial chirp) to be measured. Blocking one beam shows the spatial variation of the beamlet position with frequency (i.e., the lateral spatial chirp).

Modulations of eye movement patterns by spatial filtering during the learning and testing phases of an old/new face recognition task.

PubMed

Lemieux, Chantal L; Collin, Charles A; Nelson, Elizabeth A

2015-02-01

In two experiments, we examined the effects of varying the spatial frequency (SF) content of face images on eye movements during the learning and testing phases of an old/new recognition task. At both learning and testing, participants were presented with face stimuli band-pass filtered to 11 different SF bands, as well as an unfiltered baseline condition. We found that eye movements varied significantly as a function of SF. Specifically, the frequency of transitions between facial features showed a band-pass pattern, with more transitions for middle-band faces (≈5-20 cycles/face) than for low-band (≈<5 cpf) or high-band (≈>20 cpf) ones. These findings were similar for the learning and testing phases. The distributions of transitions across facial features were similar for the middle-band, high-band, and unfiltered faces, showing a concentration on the eyes and mouth; conversely, low-band faces elicited mostly transitions involving the nose and nasion. The eye movement patterns elicited by low, middle, and high bands are similar to those previous researchers have suggested reflect holistic, configural, and featural processing, respectively. More generally, our results are compatible with the hypotheses that eye movements are functional, and that the visual system makes flexible use of visuospatial information in face processing. Finally, our finding that only middle spatial frequencies yielded the same number and distribution of fixations as unfiltered faces adds more evidence to the idea that these frequencies are especially important for face recognition, and reveals a possible mediator for the superior performance that they elicit.

Spatiotemporal frequency tuning of BOLD and gamma band MEG responses compared in primary visual cortex.

PubMed

Muthukumaraswamy, Suresh D; Singh, Krish D

2008-05-01

In this study, the spatial and temporal frequency tuning characteristics of the MEG gamma (40-60 Hz) rhythm and the BOLD response in primary visual cortex were measured and compared. In an identical MEG/fMRI paradigm, 10 participants viewed reversing square wave gratings at 2 spatial frequencies [0.5 and 3 cycles per degree (cpd)] reversing at 5 temporal frequencies (0, 1 6, 10, 15 Hz). Three-dimensional images of MEG source power were generated with synthetic aperture magnetometry (SAM) and showed a high degree of spatial correspondence with BOLD responses in primary visual cortex with a mean spatial separation of 6.5 mm, but the two modalities showed different tuning characteristics. The gamma rhythm showed a clear increase in induced power for the high spatial frequency stimulus while BOLD showed no difference in activity for the two spatial frequencies used. Both imaging modalities showed a general increase of activity with temporal frequency, however, BOLD plateaued around 6-10 Hz while the MEG generally increased with a dip exhibited at 6 Hz. These results demonstrate that the two modalities may show activation in similar spatial locations but that the functional pattern of these activations may differ in a complex manner, suggesting that they may be tuned to different aspects of neuronal activity.

Deterministic ion beam material adding technology for high-precision optical surfaces.

PubMed

Liao, Wenlin; Dai, Yifan; Xie, Xuhui; Zhou, Lin

2013-02-20

Although ion beam figuring (IBF) provides a highly deterministic method for the precision figuring of optical components, several problems still need to be addressed, such as the limited correcting capability for mid-to-high spatial frequency surface errors and low machining efficiency for pit defects on surfaces. We propose a figuring method named deterministic ion beam material adding (IBA) technology to solve those problems in IBF. The current deterministic optical figuring mechanism, which is dedicated to removing local protuberances on optical surfaces, is enriched and developed by the IBA technology. Compared with IBF, this method can realize the uniform convergence of surface errors, where the particle transferring effect generated in the IBA process can effectively correct the mid-to-high spatial frequency errors. In addition, IBA can rapidly correct the pit defects on the surface and greatly improve the machining efficiency of the figuring process. The verification experiments are accomplished on our experimental installation to validate the feasibility of the IBA method. First, a fused silica sample with a rectangular pit defect is figured by using IBA. Through two iterations within only 47.5 min, this highly steep pit is effectively corrected, and the surface error is improved from the original 24.69 nm root mean square (RMS) to the final 3.68 nm RMS. Then another experiment is carried out to demonstrate the correcting capability of IBA for mid-to-high spatial frequency surface errors, and the final results indicate that the surface accuracy and surface quality can be simultaneously improved.

Adaptive shaping of cortical response selectivity in the vibrissa pathway

PubMed Central

Zheng, He J. V.; Wang, Qi

2015-01-01

One embodiment of context-dependent sensory processing is bottom-up adaptation, where persistent stimuli decrease neuronal firing rate over hundreds of milliseconds. Adaptation is not, however, simply the fatigue of the sensory pathway, but shapes the information flow and selectivity to stimulus features. Adaptation enhances spatial discriminability (distinguishing stimulus location) while degrading detectability (reporting presence of the stimulus), for both the ideal observer of the cortex and awake, behaving animals. However, how the dynamics of the adaptation shape the cortical response and this detection and discrimination tradeoff is unknown, as is to what degree this phenomenon occurs on a continuum as opposed to a switching of processing modes. Using voltage-sensitive dye imaging in anesthetized rats to capture the temporal and spatial characteristics of the cortical response to tactile inputs, we showed that the suppression of the cortical response, in both magnitude and spatial spread, is continuously modulated by the increasing amount of energy in the adapting stimulus, which is nonuniquely determined by its frequency and velocity. Single-trial ideal observer analysis demonstrated a tradeoff between detectability and spatial discriminability up to a moderate amount of adaptation, which corresponds to the frequency range in natural whisking. This was accompanied by a decrease in both detectability and discriminability with high-energy adaptation, which indicates a more complex coupling between detection and discrimination than a simple switching of modes. Taken together, the results suggest that adaptation operates on a continuum and modulates the tradeoff between detectability and discriminability that has implications for information processing in ethological contexts. PMID:25787959

Input-output relationships of the dorsal nucleus of the lateral lemniscus: possible substrate for the processing of dynamic spatial cues.

PubMed

Shneiderman, A; Stanforth, D A; Henkel, C K; Saint Marie, R L

1999-07-26

One organizing principle of the auditory system is the progressive representation of best tuning frequency. Superimposed on this tonotopy are nucleotopic organizations, some of which are related to the processing of different spatial cues. In the present study, we correlated asymmetries in the outputs of the dorsal nucleus of the lateral lemniscus (DNLL) to the two inferior colliculi (ICs), with asymmetries in the inputs to DNLL from the two lateral superior olives (LSOs). The positions of DNLL neurons with crossed and uncrossed projections were plotted from cases with unilateral injections of retrograde tracers in the IC. We found an orderly dorsal-to-ventral progression to the output that recapitulated the tonotopy of DNLL. In addition, we found a nucleotopic organization in the ventral (high-frequency) part of DNLL. Neurons with projections to the ventromedial (high-frequency) part of the contralateral IC were preferentially located ventrolaterally in DNLL; those with projections to the ventromedial part of the ipsilateral IC were preferentially located ventromedially in DNLL. This partial segregation of outputs corresponded with a partial segregation of inputs from the two LSOs in cases which received closely matched bilateral injections of anterograde tracers in LSO. The ventral part of DNLL received a heavy projection medially from the opposite LSO and a heavy projection laterally from the ipsilateral LSO. The findings suggest a direct relationship in the ventral part of the DNLL between inputs from the two LSOs and outputs to the two ICs. Possible roles for this segregation of pathways in DNLL are discussed in relation to the processing of static and dynamic spatial cues.

Multivariate spatial models of excess crash frequency at area level: case of Costa Rica.

PubMed

Aguero-Valverde, Jonathan

2013-10-01

Recently, areal models of crash frequency have being used in the analysis of various area-wide factors affecting road crashes. On the other hand, disease mapping methods are commonly used in epidemiology to assess the relative risk of the population at different spatial units. A natural next step is to combine these two approaches to estimate the excess crash frequency at area level as a measure of absolute crash risk. Furthermore, multivariate spatial models of crash severity are explored in order to account for both frequency and severity of crashes and control for the spatial correlation frequently found in crash data. This paper aims to extent the concept of safety performance functions to be used in areal models of crash frequency. A multivariate spatial model is used for that purpose and compared to its univariate counterpart. Full Bayes hierarchical approach is used to estimate the models of crash frequency at canton level for Costa Rica. An intrinsic multivariate conditional autoregressive model is used for modeling spatial random effects. The results show that the multivariate spatial model performs better than its univariate counterpart in terms of the penalized goodness-of-fit measure Deviance Information Criteria. Additionally, the effects of the spatial smoothing due to the multivariate spatial random effects are evident in the estimation of excess equivalent property damage only crashes. Copyright © 2013 Elsevier Ltd. All rights reserved.

Task-induced frequency modulation features for brain-computer interfacing

NASA Astrophysics Data System (ADS)

Jayaram, Vinay; Hohmann, Matthias; Just, Jennifer; Schölkopf, Bernhard; Grosse-Wentrup, Moritz

2017-10-01

Objective. Task-induced amplitude modulation of neural oscillations is routinely used in brain-computer interfaces (BCIs) for decoding subjects’ intents, and underlies some of the most robust and common methods in the field, such as common spatial patterns and Riemannian geometry. While there has been some interest in phase-related features for classification, both techniques usually presuppose that the frequencies of neural oscillations remain stable across various tasks. We investigate here whether features based on task-induced modulation of the frequency of neural oscillations enable decoding of subjects’ intents with an accuracy comparable to task-induced amplitude modulation. Approach. We compare cross-validated classification accuracies using the amplitude and frequency modulated features, as well as a joint feature space, across subjects in various paradigms and pre-processing conditions. We show results with a motor imagery task, a cognitive task, and also preliminary results in patients with amyotrophic lateral sclerosis (ALS), as well as using common spatial patterns and Laplacian filtering. Main results. The frequency features alone do not significantly out-perform traditional amplitude modulation features, and in some cases perform significantly worse. However, across both tasks and pre-processing in healthy subjects the joint space significantly out-performs either the frequency or amplitude features alone. This result only does not hold for ALS patients, for whom the dataset is of insufficient size to draw any statistically significant conclusions. Significance. Task-induced frequency modulation is robust and straight forward to compute, and increases performance when added to standard amplitude modulation features across paradigms. This allows more information to be extracted from the EEG signal cheaply and can be used throughout the field of BCIs.

Optical implementation of the synthetic discriminant function

NASA Astrophysics Data System (ADS)

Butler, S.; Riggins, J.

1984-10-01

Much attention is focused on the use of coherent optical pattern recognition (OPR) using matched spatial filters for robotics and intelligent systems. The OPR problem consists of three aspects -- information input, information processing, and information output. This paper discusses the information processing aspect which consists of choosing a filter to provide robust correlation with high efficiency. The filter should ideally be invariant to image shift, rotation and scale, provide a reasonable signal-to-noise (S/N) ratio and allow high throughput efficiency. The physical implementation of a spatial matched filter involves many choices. These include the use of conventional holograms or computer-generated holograms (CGH) and utilizing absorption or phase materials. Conventional holograms inherently modify the reference image by non-uniform emphasis of spatial frequencies. Proper use of film nonlinearity provides improved filter performance by emphasizing frequency ranges crucial to target discrimination. In the case of a CGH, the emphasis of the reference magnitude and phase can be controlled independently of the continuous tone or binary writing processes. This paper describes computer simulation and optical implementation of a geometrical shape and a Synthetic Discriminant Function (SDF) matched filter. The authors chose the binary Allebach-Keegan (AK) CGH algorithm to produce actual filters. The performances of these filters were measured to verify the simulation results. This paper provides a brief summary of the matched filter theory, the SDF, CGH algorithms, Phase-Only-Filtering, simulation procedures, and results.

Iterative-Transform Phase Retrieval Using Adaptive Diversity

NASA Technical Reports Server (NTRS)

Dean, Bruce H.

2007-01-01

A phase-diverse iterative-transform phase-retrieval algorithm enables high spatial-frequency, high-dynamic-range, image-based wavefront sensing. [The terms phase-diverse, phase retrieval, image-based, and wavefront sensing are defined in the first of the two immediately preceding articles, Broadband Phase Retrieval for Image-Based Wavefront Sensing (GSC-14899-1).] As described below, no prior phase-retrieval algorithm has offered both high dynamic range and the capability to recover high spatial-frequency components. Each of the previously developed image-based phase-retrieval techniques can be classified into one of two categories: iterative transform or parametric. Among the modifications of the original iterative-transform approach has been the introduction of a defocus diversity function (also defined in the cited companion article). Modifications of the original parametric approach have included minimizing alternative objective functions as well as implementing a variety of nonlinear optimization methods. The iterative-transform approach offers the advantage of ability to recover low, middle, and high spatial frequencies, but has disadvantage of having a limited dynamic range to one wavelength or less. In contrast, parametric phase retrieval offers the advantage of high dynamic range, but is poorly suited for recovering higher spatial frequency aberrations. The present phase-diverse iterative transform phase-retrieval algorithm offers both the high-spatial-frequency capability of the iterative-transform approach and the high dynamic range of parametric phase-recovery techniques. In implementation, this is a focus-diverse iterative-transform phaseretrieval algorithm that incorporates an adaptive diversity function, which makes it possible to avoid phase unwrapping while preserving high-spatial-frequency recovery. The algorithm includes an inner and an outer loop (see figure). An initial estimate of phase is used to start the algorithm on the inner loop, wherein multiple intensity images are processed, each using a different defocus value. The processing is done by an iterative-transform method, yielding individual phase estimates corresponding to each image of the defocus-diversity data set. These individual phase estimates are combined in a weighted average to form a new phase estimate, which serves as the initial phase estimate for either the next iteration of the iterative-transform method or, if the maximum number of iterations has been reached, for the next several steps, which constitute the outerloop portion of the algorithm. The details of the next several steps must be omitted here for the sake of brevity. The overall effect of these steps is to adaptively update the diversity defocus values according to recovery of global defocus in the phase estimate. Aberration recovery varies with differing amounts as the amount of diversity defocus is updated in each image; thus, feedback is incorporated into the recovery process. This process is iterated until the global defocus error is driven to zero during the recovery process. The amplitude of aberration may far exceed one wavelength after completion of the inner-loop portion of the algorithm, and the classical iterative transform method does not, by itself, enable recovery of multi-wavelength aberrations. Hence, in the absence of a means of off-loading the multi-wavelength portion of the aberration, the algorithm would produce a wrapped phase map. However, a special aberration-fitting procedure can be applied to the wrapped phase data to transfer at least some portion of the multi-wavelength aberration to the diversity function, wherein the data are treated as known phase values. In this way, a multiwavelength aberration can be recovered incrementally by successively applying the aberration-fitting procedure to intermediate wrapped phase maps. During recovery, as more of the aberration is transferred to the diversity function following successive iterations around the ter loop, the estimated phase ceases to wrap in places where the aberration values become incorporated as part of the diversity function. As a result, as the aberration content is transferred to the diversity function, the phase estimate resembles that of a reference flat.

Motion mechanisms with different spatiotemporal characteristics identified by an MAE technique with superimposed gratings.

PubMed

Shioiri, Satoshi; Matsumiya, Kazumichi

2009-05-29

We investigated spatiotemporal characteristics of motion mechanisms using a new type of motion aftereffect (MAE) we found. Our stimulus comprised two superimposed sinusoidal gratings with different spatial frequencies. After exposure to the moving stimulus, observers perceived the MAE in the static test in the direction opposite to that of the high spatial frequency grating even when low spatial frequency motion was perceived during adaptation. In contrast, in the flicker test, the MAE was perceived in the direction opposite to that of the low spatial frequency grating. These MAEs indicate that two different motion systems contribute to motion perception and can be isolated by using different test stimuli. Using a psychophysical technique based on the MAE, we investigated the differences between the two motion mechanisms. The results showed that the static MAE is the aftereffect of the motion system with a high spatial and low temporal frequency tuning (slow motion detector) and the flicker MAE is the aftereffect of the motion system with a low spatial and high temporal frequency tuning (fast motion detector). We also revealed that the two motion detectors differ in orientation tuning, temporal frequency tuning, and sensitivity to relative motion.

Influence of White and Gray Matter Connections on Endogenous Human Cortical Oscillations

PubMed Central

Hawasli, Ammar H.; Kim, DoHyun; Ledbetter, Noah M.; Dahiya, Sonika; Barbour, Dennis L.; Leuthardt, Eric C.

2016-01-01

Brain oscillations reflect changes in electrical potentials summated across neuronal populations. Low- and high-frequency rhythms have different modulation patterns. Slower rhythms are spatially broad, while faster rhythms are more local. From this observation, we hypothesized that low- and high-frequency oscillations reflect white- and gray-matter communications, respectively, and synchronization between low-frequency phase with high-frequency amplitude represents a mechanism enabling distributed brain-networks to coordinate local processing. Testing this common understanding, we selectively disrupted white or gray matter connections to human cortex while recording surface field potentials. Counter to our original hypotheses, we found that cortex consists of independent oscillatory-units (IOUs) that maintain their own complex endogenous rhythm structure. IOUs are differentially modulated by white and gray matter connections. White-matter connections maintain topographical anatomic heterogeneity (i.e., separable processing in cortical space) and gray-matter connections segregate cortical synchronization patterns (i.e., separable temporal processing through phase-power coupling). Modulation of distinct oscillatory modules enables the functional diversity necessary for complex processing in the human brain. PMID:27445767

The Role of Low-Spatial Frequencies in Lexical Decision and Masked Priming

ERIC Educational Resources Information Center

Boden, C.; Giaschi, D.

2009-01-01

Spatial frequency filtering was used to test the hypotheses that low-spatial frequency information in printed text can: (1) lead to a rapid lexical decision or (2) facilitate word recognition. Adult proficient readers made lexical decisions in unprimed and masked repetition priming experiments with unfiltered, low-pass, high-pass and notch…

The Development of Spatial Frequency Biases in Face Recognition

ERIC Educational Resources Information Center

Leonard, Hayley C.; Karmiloff-Smith, Annette; Johnson, Mark H.

2010-01-01

Previous research has suggested that a mid-band of spatial frequencies is critical to face recognition in adults, but few studies have explored the development of this bias in children. We present a paradigm adapted from the adult literature to test spatial frequency biases throughout development. Faces were presented on a screen with particular…

A crowdful of letters: disentangling the role of similarity, eccentricity and spatial frequencies in letter crowding.

PubMed

Zahabi, Sacha; Arguin, Martin

2014-04-01

The present study investigated the joint impact of target-flanker similarity and of spatial frequency content on the crowding effect in letter identification. We presented spatial frequency filtered letters to neurologically intact non-dyslexic readers while manipulating target-flanker distance, target eccentricity and target-flanker confusability (letter similarity metric based on published letter confusion matrices). The results show that high target-flanker confusability magnifies crowding. They also reveal an intricate pattern of interactions of the spatial frequency content of the stimuli with target eccentricity, flanker distance and similarity. The findings are congruent with the notion that crowding results from the inappropriate pooling of target and flanker features and that this integration is more likely to match a response template at a subsequent decision stage with similar than dissimilar flankers. In addition, the evidence suggests that crowding from similar flankers is biased towards relatively high spatial frequencies and that crowding shifts towards lower spatial frequencies as target eccentricity is increased. Copyright © 2014 Elsevier B.V. All rights reserved.

Spatial Cognitive Performance During Adaptation to Conflicting Tilt-Translation Stimuli as a Sensorimotor Spaceflight Analog

NASA Technical Reports Server (NTRS)

Kayanickupuram, A. J.; Ramos, K. A.; Cordova, M. L.; Wood, S. J.

2009-01-01

The need to resolve new patterns of sensory feedback in altered gravitoinertial environments requires cognitive processes to develop appropriate reference frames for spatial orientation awareness. The purpose of this study was to examine deficits in spatial cognitive performance during adaptation to conflicting tilt-translation stimuli. Fourteen subjects were tilted within a lighted enclosure that simultaneously translated at one of 3 frequencies. Tilt and translation motion was synchronized to maintain the resultant gravitoinertial force aligned with the longitudinal body axis, resulting in a mismatch analogous to spaceflight in which the canals and vision signal tilt while the otoliths do not. Changes in performance on different spatial cognitive tasks were compared 1) without motion, 2) with tilt motion alone (pitch at 0.15, 0.3 and 0.6 Hz or roll at 0.3 Hz), and 3) with conflicting tilt-translation motion. The adaptation paradigm was continued for up to 30 min or until the onset of nausea. The order of the adaptation conditions were counter-balanced across 4 different test sessions. There was a significant effect of stimulus frequency on both motion sickness and spatial cognitive performance. Only 3 of 14 were able to complete the full 30 min protocol at 0.15 Hz, while 7 of 14 completed 0.3 Hz and 13 of 14 completed 0.6 Hz. There were no changes in simple visual-spatial cognitive tests, e.g., mental rotation or match-to-sample. There were significant deficits during 0.15 Hz adaptation in both accuracy and reaction time during a spatial reference task in which subjects are asked to identify a match of a 3D reoriented cube assemblage. Our results are consistent with antidotal reports of cognitive impairment that are common during sensorimotor adaptation with G-transitions. We conclude that these cognitive deficits stem from the ambiguity of spatial reference frames for central processing of inertial motion cues.

Film characteristics pertinent to coherent optical data processing systems.

PubMed

Thomas, C E

1972-08-01

Photographic film is studied quantitatively as the input mechanism for coherent optical data recording and processing systems. The two important film characteristics are the amplitude transmission vs exposure (T(A) - E) curve and the film noise power spectral density. Both functions are measured as a function of the type of film, the type of developer, developer time and temperature, and the exposing and readout light wavelengths. A detailed analysis of a coherent optical spatial frequency analyzer reveals that the optimum do bias point for 649-F film is an amplitude transmission of about 70%. This operating point yields minimum harmonic and intermodulation distortion, whereas the 50% amplitude transmission bias point recommended by holographers yields maximum diffraction efficiency. It is also shown that the effective ac gain or contrast of the film is nearly independent of the development conditions for a given film. Finally, the linear dynamic range of one particular coherent optical spatial frequency analyzer is shown to be about 40-50 dB.

Adaptive spatial filtering using photochromic glass

NASA Astrophysics Data System (ADS)

Potton, R. J.

1999-12-01

Commercially available photochromic glasses exhibit a wide range of spectral sensitivities and darkening response times. Short wavelengths are more effective than long ones for causing darkening but at least one type of glass is effectively darkened by red light (icons/Journals/Common/lambda" ALT="lambda" ALIGN="TOP"/> = 633 nm) with an intensity of about 1 kW m-2. Used as adaptive spatial filters, these glasses attenuate a wavefront by an amount that depends on their recent exposure to light. One type of optical processing that can be performed with such filters is drift nulling in an interferometer excited by light of a wavelength within the sensitivity spectrum of the photochrome. This form of processing has been demonstrated by dithering the speckle pattern in a single-fibre multimode interferometer. The dither allows phase-sensitive detection techniques to be used in the detection of signal-induced phase variations in a frequency band extending from the inverse response time of the photochrome to the dither frequency.

Phase derivative method for reconstruction of slightly off-axis digital holograms.

PubMed

Guo, Cheng-Shan; Wang, Ben-Yi; Sha, Bei; Lu, Yu-Jie; Xu, Ming-Yuan

2014-12-15

A phase derivative (PD) method is proposed for reconstruction of off-axis holograms. In this method, a phase distribution of the tested object wave constrained within 0 to pi radian is firstly worked out by a simple analytical formula; then it is corrected to its right range from -pi to pi according to the sign characteristics of its first-order derivative. A theoretical analysis indicates that this PD method is particularly suitable for reconstruction of slightly off-axis holograms because it only requires the spatial frequency of the reference beam larger than spatial frequency of the tested object wave in principle. In addition, because the PD method belongs to a pure local method with no need of any integral operation or phase shifting algorithm in process of the phase retrieval, it could have some advantages in reducing computer load and memory requirements to the image processing system. Some experimental results are given to demonstrate the feasibility of the method.

Deconstructing continuous flash suppression

PubMed Central

Yang, Eunice; Blake, Randolph

2012-01-01

In this paper, we asked to what extent the depth of interocular suppression engendered by continuous flash suppression (CFS) varies depending on spatiotemporal properties of the suppressed stimulus and CFS suppressor. An answer to this question could have implications for interpreting the results in which CFS influences the processing of different categories of stimuli to different extents. In a series of experiments, we measured the selectivity and depth of suppression (i.e., elevation in contrast detection thresholds) as a function of the visual features of the stimulus being suppressed and the stimulus evoking suppression, namely, the popular “Mondrian” CFS stimulus (N. Tsuchiya & C. Koch, 2005). First, we found that CFS differentially suppresses the spatial components of the suppressed stimulus: Observers' sensitivity for stimuli of relatively low spatial frequency or cardinally oriented features was more strongly impaired in comparison to high spatial frequency or obliquely oriented stimuli. Second, we discovered that this feature-selective bias primarily arises from the spatiotemporal structure of the CFS stimulus, particularly within information residing in the low spatial frequency range and within the smooth rather than abrupt luminance changes over time. These results imply that this CFS stimulus operates by selectively attenuating certain classes of low-level signals while leaving others to be potentially encoded during suppression. These findings underscore the importance of considering the contribution of low-level features in stimulus-driven effects that are reported under CFS. PMID:22408039

Deconstructing continuous flash suppression.

PubMed

Yang, Eunice; Blake, Randolph

2012-03-08

In this paper, we asked to what extent the depth of interocular suppression engendered by continuous flash suppression (CFS) varies depending on spatiotemporal properties of the suppressed stimulus and CFS suppressor. An answer to this question could have implications for interpreting the results in which CFS influences the processing of different categories of stimuli to different extents. In a series of experiments, we measured the selectivity and depth of suppression (i.e., elevation in contrast detection thresholds) as a function of the visual features of the stimulus being suppressed and the stimulus evoking suppression, namely, the popular "Mondrian" CFS stimulus (N. Tsuchiya & C. Koch, 2005). First, we found that CFS differentially suppresses the spatial components of the suppressed stimulus: Observers' sensitivity for stimuli of relatively low spatial frequency or cardinally oriented features was more strongly impaired in comparison to high spatial frequency or obliquely oriented stimuli. Second, we discovered that this feature-selective bias primarily arises from the spatiotemporal structure of the CFS stimulus, particularly within information residing in the low spatial frequency range and within the smooth rather than abrupt luminance changes over time. These results imply that this CFS stimulus operates by selectively attenuating certain classes of low-level signals while leaving others to be potentially encoded during suppression. These findings underscore the importance of considering the contribution of low-level features in stimulus-driven effects that are reported under CFS.

Vibrational sum frequency generation (SFG) spectroscopic study of crystalline cellulose in biomass

NASA Astrophysics Data System (ADS)

Kim, Seong H.; Lee, Christopher M.; Kafle, Kabindra; Park, Yong Bum; Xi, Xiaoning

2013-09-01

The noncentrosymmetry requirement of sum frequency generation (SFG) spectroscopy allows selective detection of crystalline cellulose in plant cell walls and lignocellulose biomass without spectral interferences from hemicelluloses and lignin. In addition, the phase synchronization requirement of the SFG process allows noninvasive investigation of spatial arrangement of crystalline cellulose microfibrils in the sample. This paper reviews how these principles are applied to reveal structural information of crystalline cellulose in plant cell walls and biomass.

Oscillatory encoding of visual stimulus familiarity.

PubMed

Kissinger, Samuel T; Pak, Alexandr; Tang, Yu; Masmanidis, Sotiris C; Chubykin, Alexander A

2018-06-18

Familiarity of the environment changes the way we perceive and encode incoming information. However, the neural substrates underlying this phenomenon are poorly understood. Here we describe a new form of experience-dependent low frequency oscillations in the primary visual cortex (V1) of awake adult male mice. The oscillations emerged in visually evoked potentials (VEPs) and single-unit activity following repeated visual stimulation. The oscillations were sensitive to the spatial frequency content of a visual stimulus and required the muscarinic acetylcholine receptors (mAChRs) for their induction and expression. Finally, ongoing visually evoked theta (4-6 Hz) oscillations boost the VEP amplitude of incoming visual stimuli if the stimuli are presented at the high excitability phase of the oscillations. Our results demonstrate that an oscillatory code can be used to encode familiarity and serves as a gate for oncoming sensory inputs. Significance Statement. Previous experience can influence the processing of incoming sensory information by the brain and alter perception. However, the mechanistic understanding of how this process takes place is lacking. We have discovered that persistent low frequency oscillations in the primary visual cortex encode information about familiarity and the spatial frequency of the stimulus. These familiarity evoked oscillations influence neuronal responses to the oncoming stimuli in a way that depends on the oscillation phase. Our work demonstrates a new mechanism of visual stimulus feature detection and learning. Copyright © 2018 the authors.

Grading of cervical intraepithelial neoplasia using spatial frequency for optical histology

NASA Astrophysics Data System (ADS)

Pu, Yang; Jagtap, Jaidip; Pradhan, Asima; Alfano, Robert R.

2014-03-01

It is important to detect cervical dysplasia, Cervical Intraepithelial Neoplasia (CIN). CIN is the potentially premalignant and abnormal squamous cells on surface of cervix. In this study, the spatial frequency spectra of pre-cancer cervical tissues are used to detect differences among different grades of human cervical tissues. Seven sets of thick tissue sections of human cervix of normal, CIN 1, CIN 2, and CIN 3 tissues are studied. The confocal microscope images of the stromal region of normal and CIN human tissues were analyzed using Fast Fourier Transform (FFT) to generate the spatial spectra. It is observed that higher frequency components exist in CIN tissues than those in normal tissue, as well as those in higher grade CIN tissue than those in lower grade CIN tissue. The width of the spatial frequency of different types of tissues is used to create a criterion for CIN grading by training a support vector machine (SVM) classifier. The results show that the randomness of tissue structures from normal to different stages of precancer in cervical tissue can be recognized by fingerprints of the spatial frequency. The efficacy of spatial frequency analysis for CIN grading is evaluated as excellent since high AUC (area under the ROC curve), sensitivity and specificity are obtained by the statistics study. This works lays the foundation of using spatial frequency spectra for a histology evaluation.

Restoration of motion blurred image with Lucy-Richardson algorithm

NASA Astrophysics Data System (ADS)

Li, Jing; Liu, Zhao Hui; Zhou, Liang

2015-10-01

Images will be blurred by relative motion between the camera and the object of interest. In this paper, we analyzed the process of motion-blurred image, and demonstrated a restoration method based on Lucy-Richardson algorithm. The blur extent and angle can be estimated by Radon transform algorithm and auto-correlation function, respectively, and then the point spread function (PSF) of the motion-blurred image can be obtained. Thus with the help of the obtained PSF, the Lucy-Richardson restoration algorithm is used for experimental analysis on the motion-blurred images that have different blur extents, spatial resolutions and signal-to-noise ratios (SNR's). Further, its effectiveness is also evaluated by structural similarity (SSIM). Further studies show that, at first, for the image with a spatial frequency of 0.2 per pixel, the modulation transfer function (MTF) of the restored images can maintains above 0.7 when the blur extent is no bigger than 13 pixels. That means the method compensates low frequency information of the image, while attenuates high frequency information. At second, we fund that the method is more effective on condition that the product of the blur extent and spatial frequency is smaller than 3.75. Finally, the Lucy-Richardson algorithm is found insensitive to the Gaussian noise (of which the variance is not bigger than 0.1) by calculating the MTF of the restored image.

Social and spatial effects on genetic variation between foraging flocks in a wild bird population.

PubMed

Radersma, Reinder; Garroway, Colin J; Santure, Anna W; de Cauwer, Isabelle; Farine, Damien R; Slate, Jon; Sheldon, Ben C

2017-10-01

Social interactions are rarely random. In some instances, animals exhibit homophily or heterophily, the tendency to interact with similar or dissimilar conspecifics, respectively. Genetic homophily and heterophily influence the evolutionary dynamics of populations, because they potentially affect sexual and social selection. Here, we investigate the link between social interactions and allele frequencies in foraging flocks of great tits (Parus major) over three consecutive years. We constructed co-occurrence networks which explicitly described the splitting and merging of 85,602 flocks through time (fission-fusion dynamics), at 60 feeding sites. Of the 1,711 birds in those flocks, we genotyped 962 individuals at 4,701 autosomal single nucleotide polymorphisms (SNPs). By combining genomewide genotyping with repeated field observations of the same individuals, we were able to investigate links between social structure and allele frequencies at a much finer scale than was previously possible. We explicitly accounted for potential spatial effects underlying genetic structure at the population level. We modelled social structure and spatial configuration of great tit fission-fusion dynamics with eigenvector maps. Variance partitioning revealed that allele frequencies were strongly affected by group fidelity (explaining 27%-45% of variance) as individuals tended to maintain associations with the same conspecifics. These conspecifics were genetically more dissimilar than expected, shown by genomewide heterophily for pure social (i.e., space-independent) grouping preferences. Genomewide homophily was linked to spatial configuration, indicating spatial segregation of genotypes. We did not find evidence for homophily or heterophily for putative socially relevant candidate genes or any other SNP markers. Together, these results demonstrate the importance of distinguishing social and spatial processes in determining population structure. © 2017 John Wiley & Sons Ltd.

Multi-functional angiographic OFDI using frequency-multiplexed dual-beam illumination

PubMed Central

Kim, SunHee; Park, Taejin; Jang, Sun-Joo; Nam, Ahhyun S.; Vakoc, Benjamin J.; Oh, Wang-Yuhl

2015-01-01

Detection of blood flow inside the tissue sample can be achieved by measuring the local change of complex signal over time in angiographic optical coherence tomography (OCT). In conventional angiographic OCT, the transverse displacement of the imaging beam during the time interval between a pair of OCT signal measurements must be significantly reduced to minimize the noise due to the beam scanning-induced phase decorrelation at the expense of the imaging speed. Recent introduction of dual-beam scan method either using polarization encoding or two identical imaging systems in spectral-domain (SD) OCT scheme shows potential for high-sensitivity vasculature imaging without suffering from spurious phase noise caused by the beam scanning-induced spatial decorrelation. In this paper, we present multi-functional angiographic optical frequency domain imaging (OFDI) using frequency-multiplexed dual-beam illumination. This frequency multiplexing scheme, utilizing unique features of OFDI, provides spatially separated dual imaging beams occupying distinct electrical frequency bands that can be demultiplexed in the frequency domain processing. We demonstrate the 3D multi-functional imaging of the normal mouse skin in the dorsal skin fold chamber visualizing distinct layer structures from the intensity imaging, information about mechanical integrity from the polarization-sensitive imaging, and depth-resolved microvasculature from the angiographic imaging that are simultaneously acquired and automatically co-registered. PMID:25968731

Image Discrimination Models With Stochastic Channel Selection

NASA Technical Reports Server (NTRS)

Ahumada, Albert J., Jr.; Beard, Bettina L.; Null, Cynthia H. (Technical Monitor)

1995-01-01

Many models of human image processing feature a large fixed number of channels representing cortical units varying in spatial position (visual field direction and eccentricity) and spatial frequency (radial frequency and orientation). The values of these parameters are usually sampled at fixed values selected to ensure adequate overlap considering the bandwidth and/or spread parameters, which are usually fixed. Even high levels of overlap does not always ensure that the performance of the model will vary smoothly with image translation or scale changes. Physiological measurements of bandwidth and/or spread parameters result in a broad distribution of estimated parameter values and the prediction of some psychophysical results are facilitated by the assumption that these parameters also take on a range of values. Selecting a sample of channels from a continuum of channels rather than using a fixed set can make model performance vary smoothly with changes in image position, scale, and orientation. It also facilitates the addition of spatial inhomogeneity, nonlinear feature channels, and focus of attention to channel models.

Spatial heterogeneity of leaf area index across scales from simulation and remote sensing

NASA Astrophysics Data System (ADS)

Reichenau, Tim G.; Korres, Wolfgang; Montzka, Carsten; Schneider, Karl

2016-04-01

Leaf area index (LAI, single sided leaf area per ground area) influences mass and energy exchange of vegetated surfaces. Therefore LAI is an input variable for many land surface schemes of coupled large scale models, which do not simulate LAI. Since these models typically run on rather coarse resolution grids, LAI is often inferred from coarse resolution remote sensing. However, especially in agriculturally used areas, a grid cell of these products often covers more than a single land-use. In that case, the given LAI does not apply to any single land-use. Therefore, the overall spatial heterogeneity in these datasets differs from that on resolutions high enough to distinguish areas with differing land-use. Detailed process-based plant growth models simulate LAI for separate plant functional types or specific species. However, limited availability of observations causes reduced spatial heterogeneity of model input data (soil, weather, land-use). Since LAI is strongly heterogeneous in space and time and since processes depend on LAI in a nonlinear way, a correct representation of LAI spatial heterogeneity is also desirable on coarse resolutions. The current study assesses this issue by comparing the spatial heterogeneity of LAI from remote sensing (RapidEye) and process-based simulations (DANUBIA simulation system) across scales. Spatial heterogeneity is assessed by analyzing LAI frequency distributions (spatial variability) and semivariograms (spatial structure). Test case is the arable land in the fertile loess plain of the Rur catchment near the Germany-Netherlands border.

Figure/ground segregation from temporal delay is best at high spatial frequencies.

PubMed

Kojima, H

1998-12-01

Two experiments investigated the role of spatial frequency in performance of a figure/ground segregation task based on temporal cues. Figure orientation was much easier to judge when figure and ground portions of the target were defined exclusively by random texture composed entirely of high spatial frequencies. When target components were defined by low spatial frequencies only, the task was nearly impossible except with long temporal delay between figure and ground. These results are inconsistent with the hypothesis that M-cell activity is primarily responsible for figure/ground segregation from temporal delay. Instead, these results point to a distinction between temporal integration and temporal differentiation. Additionally, the present results can be related to recent work on the binding of spatial features over time.

Multi-focus image fusion algorithm using NSCT and MPCNN

NASA Astrophysics Data System (ADS)

Liu, Kang; Wang, Lianli

2018-04-01

Based on nonsubsampled contourlet transform (NSCT) and modified pulse coupled neural network (MPCNN), the paper proposes an effective method of image fusion. Firstly, the paper decomposes the source image into the low-frequency components and high-frequency components using NSCT, and then processes the low-frequency components by regional statistical fusion rules. For high-frequency components, the paper calculates the spatial frequency (SF), which is input into MPCNN model to get relevant coefficients according to the fire-mapping image of MPCNN. At last, the paper restructures the final image by inverse transformation of low-frequency and high-frequency components. Compared with the wavelet transformation (WT) and the traditional NSCT algorithm, experimental results indicate that the method proposed in this paper achieves an improvement both in human visual perception and objective evaluation. It indicates that the method is effective, practical and good performance.

Sinusoidal Siemens star spatial frequency response measurement errors due to misidentified target centers

DOE PAGES

Birch, Gabriel Carisle; Griffin, John Clark

2015-07-23

Numerous methods are available to measure the spatial frequency response (SFR) of an optical system. A recent change to the ISO 12233 photography resolution standard includes a sinusoidal Siemens star test target. We take the sinusoidal Siemens star proposed by the ISO 12233 standard, measure system SFR, and perform an analysis of errors induced by incorrectly identifying the center of a test target. We show a closed-form solution for the radial profile intensity measurement given an incorrectly determined center and describe how this error reduces the measured SFR of the system. As a result, using the closed-form solution, we proposemore » a two-step process by which test target centers are corrected and the measured SFR is restored to the nominal, correctly centered values.« less

Dynamic order in a surface process

NASA Astrophysics Data System (ADS)

Eiswirth, M.; Ertl, G.

1988-09-01

Under certain well-defined conditions ( p co,p_{{text{O}}_{text{2}} } , T) the rate of catalytic oxidation of CO on a Pt(110) surface may exhibit sustained temporal oscillations with an autonomous frequency v 0. Small amplitude modulation ofp_{{text{O}}_{text{2}} } with frequency v p causes a variety of phenomena characteristic for systems of nonlinear dynamics which may be identified with temporal order and show formal similarities to spatial order of surface phases: Periodic behavior for certain rational numbers of v p/v0 — corresponding to commensurate surface structures; quasiperiodic behavior characterized by an irrational ratio of the periods of perturbation and response — corresponding to incommensurate structures; and critical slowing down near the boundary of a transition to quasiperiodicity which has its counterpart in the critical fluctuations near a (spatial) phase transition.

Estimation of optimal hologram recording modes on photothermal materials

NASA Astrophysics Data System (ADS)

Dzhamankyzov, Nasipbek Kurmanalievich; Ismanov, Yusupzhan Khakimzhanovich; Zhumaliev, Kubanychbek Myrzabekovich; Alymkulov, Samsaly Amanovich

2018-01-01

A theoretical analysis of the hologram recording process on photothermal media to estimate the required laser radiation power for the information recording as the function of the spatial frequency and radiation exposure duration is considered. Results of the analysis showed that materials with a low thermal diffusivity are necessary to increase the recording density in these media and the recording should be performed with short pulses to minimize the thermal diffusion length. A solution for the heat conduction equation for photothermal materials heated by an interference laser field was found. The solution obtained allows one to determine the required value of the recording temperature for given spatial frequencies, depending on the thermal physical parameters of the medium and on the power and duration of the heating radiation.

Pixelated camouflage patterns from the perspective of hyperspectral imaging

NASA Astrophysics Data System (ADS)

Racek, František; Jobánek, Adam; Baláž, Teodor; Krejčí, Jaroslav

2016-10-01

Pixelated camouflage patterns fulfill the role of both principles the matching and the disrupting that are exploited for blending the target into the background. It means that pixelated pattern should respect natural background in spectral and spatial characteristics embodied in micro and macro patterns. The HS imaging plays the similar, however the reverse role in the field of reconnaissance systems. The HS camera fundamentally records and extracts both the spectral and spatial information belonging to the recorded scenery. Therefore, the article deals with problems of hyperspectral (HS) imaging and subsequent processing of HS images of pixelated camouflage patterns which are among others characterized by their specific spatial frequency heterogeneity.

A spherical model for orientation and spatial-frequency tuning in a cortical hypercolumn.

PubMed Central

Bressloff, Paul C; Cowan, Jack D

2003-01-01

A theory is presented of the way in which the hypercolumns in primary visual cortex (V1) are organized to detect important features of visual images, namely local orientation and spatial-frequency. Given the existence in V1 of dual maps for these features, both organized around orientation pinwheels, we constructed a model of a hypercolumn in which orientation and spatial-frequency preferences are represented by the two angular coordinates of a sphere. The two poles of this sphere are taken to correspond, respectively, to high and low spatial-frequency preferences. In Part I of the paper, we use mean-field methods to derive exact solutions for localized activity states on the sphere. We show how cortical amplification through recurrent interactions generates a sharply tuned, contrast-invariant population response to both local orientation and local spatial frequency, even in the case of a weakly biased input from the lateral geniculate nucleus (LGN). A major prediction of our model is that this response is non-separable with respect to the local orientation and spatial frequency of a stimulus. That is, orientation tuning is weaker around the pinwheels, and there is a shift in spatial-frequency tuning towards that of the closest pinwheel at non-optimal orientations. In Part II of the paper, we demonstrate that a simple feed-forward model of spatial-frequency preference, unlike that for orientation preference, does not generate a faithful representation when amplified by recurrent interactions in V1. We then introduce the idea that cortico-geniculate feedback modulates LGN activity to generate a faithful representation, thus providing a new functional interpretation of the role of this feedback pathway. Using linear filter theory, we show that if the feedback from a cortical cell is taken to be approximately equal to the reciprocal of the corresponding feed-forward receptive field (in the two-dimensional Fourier domain), then the mismatch between the feed-forward and cortical frequency representations is eliminated. We therefore predict that cortico-geniculate feedback connections innervate the LGN in a pattern determined by the orientation and spatial-frequency biases of feed-forward receptive fields. Finally, we show how recurrent cortical interactions can generate cross-orientation suppression. PMID:14561324

Spatial-frequency composite watermarking for digital image copyright protection

NASA Astrophysics Data System (ADS)

Su, Po-Chyi; Kuo, C.-C. Jay

2000-05-01

Digital watermarks can be classified into two categories according to the embedding and retrieval domain, i.e. spatial- and frequency-domain watermarks. Because the two watermarks have different characteristics and limitations, combination of them can have various interesting properties when applied to different applications. In this research, we examine two spatial-frequency composite watermarking schemes. In both cases, a frequency-domain watermarking technique is applied as a baseline structure in the system. The embedded frequency- domain watermark is robust against filtering and compression. A spatial-domain watermarking scheme is then built to compensate some deficiency of the frequency-domain scheme. The first composite scheme is to embed a robust watermark in images to convey copyright or author information. The frequency-domain watermark contains owner's identification number while the spatial-domain watermark is embedded for image registration to resist cropping attack. The second composite scheme is to embed fragile watermark for image authentication. The spatial-domain watermark helps in locating the tampered part of the image while the frequency-domain watermark indicates the source of the image and prevents double watermarking attack. Experimental results show that the two watermarks do not interfere with each other and different functionalities can be achieved. Watermarks in both domains are detected without resorting to the original image. Furthermore, the resulting watermarked image can still preserve high fidelity without serious visual degradation.

Controlling Energy Radiations of Electromagnetic Waves via Frequency Coding Metamaterials

PubMed Central

Wu, Haotian; Liu, Shuo; Wan, Xiang; Zhang, Lei; Wang, Dan; Li, Lianlin

2017-01-01

Metamaterials are artificial structures composed of subwavelength unit cells to control electromagnetic (EM) waves. The spatial coding representation of metamaterial has the ability to describe the material in a digital way. The spatial coding metamaterials are typically constructed by unit cells that have similar shapes with fixed functionality. Here, the concept of frequency coding metamaterial is proposed, which achieves different controls of EM energy radiations with a fixed spatial coding pattern when the frequency changes. In this case, not only different phase responses of the unit cells are considered, but also different phase sensitivities are also required. Due to different frequency sensitivities of unit cells, two units with the same phase response at the initial frequency may have different phase responses at higher frequency. To describe the frequency coding property of unit cell, digitalized frequency sensitivity is proposed, in which the units are encoded with digits “0” and “1” to represent the low and high phase sensitivities, respectively. By this merit, two degrees of freedom, spatial coding and frequency coding, are obtained to control the EM energy radiations by a new class of frequency‐spatial coding metamaterials. The above concepts and physical phenomena are confirmed by numerical simulations and experiments. PMID:28932671

[Study on the Spectral Characteristics of the Narrow-Band Filter in SHS].

PubMed

Luo, Hai-yan; Shi, Hai-liang; Li, Zhi-wei; Li, Shuang; Xiong, Wei; Hong, Jin

2015-04-01

The spectral response of spatial heterodyne spectroscopy (SHS) is determined by the spectrum property of narrow-band filter. As discussed in previous studies, the symmetric heterodyned interferogram of high frequency waves modulated by SHS and lack of sample lead to spectral confusion, which is associated with the true and ghost spectra. Because of the deviation from theoretical index of narrow-band filter in the process of coating, the boarded spectral response and middle wave shift are presented, and conditions in the theoretical Littrow wavelength made the effective wavelength range of SHS reduced. According to the measured curve of filter, a new wavenumber of zero spatial frequency can be reset by tunable laser, and it is easy for SHS to improve the spectral aliasing distortion. The results show that it is utilized to the maximum extent of the effective bandwidth by adjusting the grating angle of rotation to change the Littrow wavelength of the basic frequency, and the spectral region increased to 14.9 nm from original 12.9 nm.

Frequency-specific attentional modulation in human primary auditory cortex and midbrain.

PubMed

Riecke, Lars; Peters, Judith C; Valente, Giancarlo; Poser, Benedikt A; Kemper, Valentin G; Formisano, Elia; Sorger, Bettina

2018-07-01

Paying selective attention to an audio frequency selectively enhances activity within primary auditory cortex (PAC) at the tonotopic site (frequency channel) representing that frequency. Animal PAC neurons achieve this 'frequency-specific attentional spotlight' by adapting their frequency tuning, yet comparable evidence in humans is scarce. Moreover, whether the spotlight operates in human midbrain is unknown. To address these issues, we studied the spectral tuning of frequency channels in human PAC and inferior colliculus (IC), using 7-T functional magnetic resonance imaging (FMRI) and frequency mapping, while participants focused on different frequency-specific sounds. We found that shifts in frequency-specific attention alter the response gain, but not tuning profile, of PAC frequency channels. The gain modulation was strongest in low-frequency channels and varied near-monotonically across the tonotopic axis, giving rise to the attentional spotlight. We observed less prominent, non-tonotopic spatial patterns of attentional modulation in IC. These results indicate that the frequency-specific attentional spotlight in human PAC as measured with FMRI arises primarily from tonotopic gain modulation, rather than adapted frequency tuning. Moreover, frequency-specific attentional modulation of afferent sound processing in human IC seems to be considerably weaker, suggesting that the spotlight diminishes toward this lower-order processing stage. Our study sheds light on how the human auditory pathway adapts to the different demands of selective hearing. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Analysing the spatial patterns of erosion scars using point process theory at the coastal chalk cliff of Mesnil-Val, (Normandy, Northern France)

NASA Astrophysics Data System (ADS)

Rohmer, J.; Dewez, D.

2014-09-01

Over the last decade, many cliff erosion studies have focused on frequency-size statistics using inventories of sea cliff retreat sizes. By comparison, only a few paid attention to quantifying the spatial and temporal organisation of erosion scars over a cliff face. Yet, this spatial organisation carries essential information about the external processes and the environmental conditions that promote or initiate sea-cliff instabilities. In this article, we use summary statistics of spatial point process theory as a tool to examine the spatial and temporal pattern of a rockfall inventory recorded with repeated terrestrial laser scanning surveys at the chalk coastal cliff site of Mesnil-Val (Normandy, France). Results show that: (1) the spatial density of erosion scars is specifically conditioned alongshore by the distance to an engineered concrete groin, with an exponential-like decreasing trend, and vertically focused both at wave breaker height and on strong lithological contrasts; (2) small erosion scars (10-3-10-2 m3) aggregate in clusters within a radius of 5 to 10 m, which suggests some sort of attraction or focused causative process, and disperse above this critical distance; (3) on the contrary, larger erosion scars (10-2-101 m3) tend to disperse above a radius of 1 to 5 m, possibly due to the spreading of successive failures across the cliff face; (4) large scars significantly occur albeit moderately, where previous large rockfalls have occurred during preceeding winter; (5) this temporal trend is not apparent for small events. In conclusion, this study shows, with a worked example, how spatial point process summary statistics are a tool to test and quantify the significance of geomorphological observation organisation.

Analysing the spatial patterns of erosion scars using point process theory at the coastal chalk cliff of Mesnil-Val, Normandy, northern France

NASA Astrophysics Data System (ADS)

Rohmer, J.; Dewez, T.

2015-02-01

Over the last decade, many cliff erosion studies have focused on frequency-size statistics using inventories of sea cliff retreat sizes. By comparison, only a few paid attention to quantifying the spatial and temporal organisation of erosion scars over a cliff face. Yet, this spatial organisation carries essential information about the external processes and the environmental conditions that promote or initiate sea-cliff instabilities. In this article, we use summary statistics of spatial point process theory as a tool to examine the spatial and temporal pattern of a rockfall inventory recorded with repeated terrestrial laser scanning surveys at the chalk coastal cliff site of Mesnil-Val (Normandy, France). Results show that: (1) the spatial density of erosion scars is specifically conditioned alongshore by the distance to an engineered concrete groyne, with an exponential-like decreasing trend, and vertically focused both at wave breaker height and on strong lithological contrasts; (2) small erosion scars (10-3 to 10-2 m3) aggregate in clusters within a radius of 5 to 10 m, which suggests some sort of attraction or focused causative process, and disperse above this critical distance; (3) on the contrary, larger erosion scars (10-2 to 101 m3) tend to disperse above a radius of 1 to 5 m, possibly due to the spreading of successive failures across the cliff face; (4) large scars significantly occur albeit moderately, where previous large rockfalls have occurred during preceding winter; (5) this temporal trend is not apparent for small events. In conclusion, this study shows, with a worked example, how spatial point process summary statistics are a tool to test and quantify the significance of geomorphological observation organisation.

Interocular transfer of spatial adaptation is weak at low spatial frequencies.

PubMed

Baker, Daniel H; Meese, Tim S

2012-06-15

Adapting one eye to a high contrast grating reduces sensitivity to similar target gratings shown to the same eye, and also to those shown to the opposite eye. According to the textbook account, interocular transfer (IOT) of adaptation is around 60% of the within-eye effect. However, most previous studies on this were limited to using high spatial frequencies, sustained presentation, and criterion-dependent methods for assessing threshold. Here, we measure IOT across a wide range of spatiotemporal frequencies, using a criterion-free 2AFC method. We find little or no IOT at low spatial frequencies, consistent with other recent observations. At higher spatial frequencies, IOT was present, but weaker than previously reported (around 35%, on average, at 8c/deg). Across all conditions, monocular adaptation raised thresholds by around a factor of 2, and observers showed normal binocular summation, demonstrating that they were not binocularly compromised. These findings prompt a reassessment of our understanding of the binocular architecture implied by interocular adaptation. In particular, the output of monocular channels may be available to perceptual decision making at low spatial frequencies. Copyright © 2012 Elsevier Ltd. All rights reserved.

Internal noise sources limiting contrast sensitivity.

PubMed

Silvestre, Daphné; Arleo, Angelo; Allard, Rémy

2018-02-07

Contrast sensitivity varies substantially as a function of spatial frequency and luminance intensity. The variation as a function of luminance intensity is well known and characterized by three laws that can be attributed to the impact of three internal noise sources: early spontaneous neural activity limiting contrast sensitivity at low luminance intensities (i.e. early noise responsible for the linear law), probabilistic photon absorption at intermediate luminance intensities (i.e. photon noise responsible for de Vries-Rose law) and late spontaneous neural activity at high luminance intensities (i.e. late noise responsible for Weber's law). The aim of this study was to characterize how the impact of these three internal noise sources vary with spatial frequency and determine which one is limiting contrast sensitivity as a function of luminance intensity and spatial frequency. To estimate the impact of the different internal noise sources, the current study used an external noise paradigm to factorize contrast sensitivity into equivalent input noise and calculation efficiency over a wide range of luminance intensities and spatial frequencies. The impact of early and late noise was found to drop linearly with spatial frequency, whereas the impact of photon noise rose with spatial frequency due to ocular factors.

Temporal dynamics of divided spatial attention

PubMed Central

Garcia, Javier O.; Serences, John T.

2013-01-01

In naturalistic settings, observers often have to monitor multiple objects dispersed throughout the visual scene. However, the degree to which spatial attention can be divided across spatially noncontiguous objects has long been debated, particularly when those objects are in close proximity. Moreover, the temporal dynamics of divided attention are unclear: is the process of dividing spatial attention gradual and continuous, or does it onset in a discrete manner? To address these issues, we recorded steady-state visual evoked potentials (SSVEPs) as subjects covertly monitored two flickering targets while ignoring an intervening distractor that flickered at a different frequency. All three stimuli were clustered within either the lower left or the lower right quadrant, and our dependent measure was SSVEP power at the target and distractor frequencies measured over time. In two experiments, we observed a temporally discrete increase in power for target- vs. distractor-evoked SSVEPs extending from ∼350 to 150 ms prior to correct (but not incorrect) responses. The divergence in SSVEP power immediately prior to a correct response suggests that spatial attention can be divided across noncontiguous locations, even when the targets are closely spaced within a single quadrant. In addition, the division of spatial attention appears to be relatively discrete, as opposed to slow and continuous. Finally, the predictive relationship between SSVEP power and behavior demonstrates that these neurophysiological measures of divided attention are meaningfully related to cognitive function. PMID:23390315

Temporal dynamics of divided spatial attention.

PubMed

Itthipuripat, Sirawaj; Garcia, Javier O; Serences, John T

2013-05-01

In naturalistic settings, observers often have to monitor multiple objects dispersed throughout the visual scene. However, the degree to which spatial attention can be divided across spatially noncontiguous objects has long been debated, particularly when those objects are in close proximity. Moreover, the temporal dynamics of divided attention are unclear: is the process of dividing spatial attention gradual and continuous, or does it onset in a discrete manner? To address these issues, we recorded steady-state visual evoked potentials (SSVEPs) as subjects covertly monitored two flickering targets while ignoring an intervening distractor that flickered at a different frequency. All three stimuli were clustered within either the lower left or the lower right quadrant, and our dependent measure was SSVEP power at the target and distractor frequencies measured over time. In two experiments, we observed a temporally discrete increase in power for target- vs. distractor-evoked SSVEPs extending from ∼350 to 150 ms prior to correct (but not incorrect) responses. The divergence in SSVEP power immediately prior to a correct response suggests that spatial attention can be divided across noncontiguous locations, even when the targets are closely spaced within a single quadrant. In addition, the division of spatial attention appears to be relatively discrete, as opposed to slow and continuous. Finally, the predictive relationship between SSVEP power and behavior demonstrates that these neurophysiological measures of divided attention are meaningfully related to cognitive function.

Age Differences in Face Processing: The Role of Perceptual Degradation and Holistic Processing.

PubMed

Boutet, Isabelle; Meinhardt-Injac, Bozana

2018-01-24

We simultaneously investigated the role of three hypotheses regarding age-related differences in face processing: perceptual degradation, impaired holistic processing, and an interaction between the two. Young adults (YA) aged 20-33-year olds, middle-age adults (MA) aged 50-64-year olds, and older adults (OA) aged 65-82-year olds were tested on the context congruency paradigm, which allows measurement of face-specific holistic processing across the life span (Meinhardt-Injac, Persike & Meinhardt, 2014. Acta Psychologica, 151, 155-163). Perceptual degradation was examined by measuring performance with faces that were not filtered (FSF), with faces filtered to preserve low spatial frequencies (LSF), and with faces filtered to preserve high spatial frequencies (HSF). We found that reducing perceptual signal strength had a greater impact on MA and OA for HSF faces, but not LSF faces. Context congruency effects were significant and of comparable magnitude across ages for FSF, LSF, and HSF faces. By using watches as control objects, we show that these holistic effects reflect face-specific mechanisms in all age groups. Our results support the perceptual degradation hypothesis for faces containing only HSF and suggest that holistic processing is preserved in aging even under conditions of reduced signal strength. © The Author(s) 2018. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

[Evoked Potential Blind Extraction Based on Fractional Lower Order Spatial Time-Frequency Matrix].

PubMed

Long, Junbo; Wang, Haibin; Zha, Daifeng

2015-04-01

The impulsive electroencephalograph (EEG) noises in evoked potential (EP) signals is very strong, usually with a heavy tail and infinite variance characteristics like the acceleration noise impact, hypoxia and etc., as shown in other special tests. The noises can be described by a stable distribution model. In this paper, Wigner-Ville distribution (WVD) and pseudo Wigner-Ville distribution (PWVD) time-frequency distribution based on the fractional lower order moment are presented to be improved. We got fractional lower order WVD (FLO-WVD) and fractional lower order PWVD (FLO-PWVD) time-frequency distribution which could be suitable for a stable distribution process. We also proposed the fractional lower order spatial time-frequency distribution matrix (FLO-STFM) concept. Therefore, combining with time-frequency underdetermined blind source separation (TF-UBSS), we proposed a new fractional lower order spatial time-frequency underdetermined blind source separation (FLO-TF-UBSS) which can work in a stable distribution environment. We used the FLO-TF-UBSS algorithm to extract EPs. Simulations showed that the proposed method could effectively extract EPs in EEG noises, and the separated EPs and EEG signals based on FLO-TF-UBSS were almost the same as the original signal, but blind separation based on TF-UBSS had certain deviation. The correlation coefficient of the FLO-TF-UBSS algorithm was higher than the TF-UBSS algorithm when generalized signal-to-noise ratio (GSNR) changed from 10 dB to 30 dB and a varied from 1. 06 to 1. 94, and was approximately e- qual to 1. Hence, the proposed FLO-TF-UBSS method might be better than the TF-UBSS algorithm based on second order for extracting EP signal under an EEG noise environment.

Apparatus for direct-to-digital spatially-heterodyned holography

DOEpatents

Thomas, Clarence E.; Hanson, Gregory R.

2006-12-12

An apparatus operable to record a spatially low-frequency heterodyne hologram including spatially heterodyne fringes for Fourier analysis includes: a laser; a beamsplitter optically coupled to the laser; an object optically coupled to the beamsplitter; a focusing lens optically coupled to both the beamsplitter and the object; a digital recorder optically coupled to the focusing lens; and a computer that performs a Fourier transform, applies a digital filter, and performs an inverse Fourier transform. A reference beam and an object beam are focused by the focusing lens at a focal plane of the digital recorder to form a spatially low-frequency heterodyne hologram including spatially heterodyne fringes for Fourier analysis which is recorded by the digital recorder, and the computer transforms the recorded spatially low-frequency heterodyne hologram including spatially heterodyne fringes and shifts axes in Fourier space to sit on top of a heterodyne carrier frequency defined by an angle between the reference beam and the object beam and cuts off signals around an original origin before performing the inverse Fourier transform.

Blind deconvolution of astronomical images with band limitation determined by optical system parameters

NASA Astrophysics Data System (ADS)

Luo, L.; Fan, M.; Shen, M. Z.

2007-07-01

Atmospheric turbulence greatly limits the spatial resolution of astronomical images acquired by the large ground-based telescope. The record image obtained from telescope was thought as a convolution result of the object function and the point spread function. The statistic relationship of the images measured data, the estimated object and point spread function was in accord with the Bayes conditional probability distribution, and the maximum-likelihood formulation was found. A blind deconvolution approach based on the maximum-likelihood estimation technique with real optical band limitation constraint is presented for removing the effect of atmospheric turbulence on this class images through the minimization of the convolution error function by use of the conjugation gradient optimization algorithm. As a result, the object function and the point spread function could be estimated from a few record images at the same time by the blind deconvolution algorithm. According to the principle of Fourier optics, the relationship between the telescope optical system parameters and the image band constraint in the frequency domain was formulated during the image processing transformation between the spatial domain and the frequency domain. The convergence of the algorithm was increased by use of having the estimated function variable (also is the object function and the point spread function) nonnegative and the point-spread function band limited. Avoiding Fourier transform frequency components beyond the cut off frequency lost during the image processing transformation when the size of the sampled image data, image spatial domain and frequency domain were the same respectively, the detector element (e.g. a pixels in the CCD) should be less than the quarter of the diffraction speckle diameter of the telescope for acquiring the images on the focal plane. The proposed method can easily be applied to the case of wide field-view turbulent-degraded images restoration because of no using the object support constraint in the algorithm. The performance validity of the method is examined by the computer simulation and the restoration of the real Alpha Psc astronomical image data. The results suggest that the blind deconvolution with the real optical band constraint can remove the effect of the atmospheric turbulence on the observed images and the spatial resolution of the object image can arrive at or exceed the diffraction-limited level.

Image routing via atomic spin coherence

PubMed Central

Wang, Lei; Sun, Jia-Xiang; Luo, Meng-Xi; Sun, Yuan-Hang; Wang, Xiao-Xiao; Chen, Yi; Kang, Zhi-Hui; Wang, Hai-Hua; Wu, Jin-Hui; Gao, Jin-Yue

2015-01-01

Coherent storage of optical image in a coherently-driven medium is a promising method with possible applications in many fields. In this work, we experimentally report a controllable spatial-frequency routing of image via atomic spin coherence in a solid-state medium driven by electromagnetically induced transparency (EIT). Under the EIT-based light-storage regime, a transverse spatial image carried by the probe field is stored into atomic spin coherence. By manipulating the frequency and spatial propagation direction of the read control field, the stored image is transferred into a new spatial-frequency channel. When two read control fields are used to retrieve the stored information, the image information is converted into a superposition of two spatial-frequency modes. Through this technique, the image is manipulated coherently and all-optically in a controlled fashion. PMID:26658846

Analysis on unevenness of skin color using the melanin and hemoglobin components separated by independent component analysis of skin color image

NASA Astrophysics Data System (ADS)

Ojima, Nobutoshi; Fujiwara, Izumi; Inoue, Yayoi; Tsumura, Norimichi; Nakaguchi, Toshiya; Iwata, Kayoko

2011-03-01

Uneven distribution of skin color is one of the biggest concerns about facial skin appearance. Recently several techniques to analyze skin color have been introduced by separating skin color information into chromophore components, such as melanin and hemoglobin. However, there are not many reports on quantitative analysis of unevenness of skin color by considering type of chromophore, clusters of different sizes and concentration of the each chromophore. We propose a new image analysis and simulation method based on chromophore analysis and spatial frequency analysis. This method is mainly composed of three techniques: independent component analysis (ICA) to extract hemoglobin and melanin chromophores from a single skin color image, an image pyramid technique which decomposes each chromophore into multi-resolution images, which can be used for identifying different sizes of clusters or spatial frequencies, and analysis of the histogram obtained from each multi-resolution image to extract unevenness parameters. As the application of the method, we also introduce an image processing technique to change unevenness of melanin component. As the result, the method showed high capabilities to analyze unevenness of each skin chromophore: 1) Vague unevenness on skin could be discriminated from noticeable pigmentation such as freckles or acne. 2) By analyzing the unevenness parameters obtained from each multi-resolution image for Japanese ladies, agerelated changes were observed in the parameters of middle spatial frequency. 3) An image processing system modulating the parameters was proposed to change unevenness of skin images along the axis of the obtained age-related change in real time.

Conservation threats due to human-caused increases in fire frequency in Mediterranean-climate ecosystems.

PubMed

Syphard, Alexandra D; Radeloff, Volker C; Hawbaker, Todd J; Stewart, Susan I

2009-06-01

Periodic wildfire is an important natural process in Mediterranean-climate ecosystems, but increasing fire recurrence threatens the fragile ecology of these regions. Because most fires are human-caused, we investigated how human population patterns affect fire frequency. Prior research in California suggests the relationship between population density and fire frequency is not linear. There are few human ignitions in areas with low population density, so fire frequency is low. As population density increases, human ignitions and fire frequency also increase, but beyond a density threshold, the relationship becomes negative as fuels become sparser and fire suppression resources are concentrated. We tested whether this hypothesis also applies to the other Mediterranean-climate ecosystems of the world. We used global satellite databases of population, fire activity, and land cover to evaluate the spatial relationship between humans and fire in the world's five Mediterranean-climate ecosystems. Both the mean and median population densities were consistently and substantially higher in areas with than without fire, but fire again peaked at intermediate population densities, which suggests that the spatial relationship is complex and nonlinear. Some land-cover types burned more frequently than expected, but no systematic differences were observed across the five regions. The consistent association between higher population densities and fire suggests that regardless of differences between land-cover types, natural fire regimes, or overall population, the presence of people in Mediterranean-climate regions strongly affects the frequency of fires; thus, population growth in areas now sparsely settled presents a conservation concern. Considering the sensitivity of plant species to repeated burning and the global conservation significance of Mediterranean-climate ecosystems, conservation planning needs to consider the human influence on fire frequency. Fine-scale spatial analysis of relationships between people and fire may help identify areas where increases in fire frequency will threaten ecologically valuable areas. ©2009 Society for Conservation Biology.

Visual evoked potential measurement of contrast sensitivity in a case of retinal laser injury reveals visual function loss despite normal acuity

NASA Astrophysics Data System (ADS)

Glickman, Randolph D.; Harrison, Joseph M.; Zwick, Harry; Longbotham, Harold G.; Ballentine, Charles S.; Pierce, Bennie

1996-04-01

Although visual function following retinal laser injuries has traditionally been assessed by measuring visual acuity, this measure only indicates the highest spatial frequency resolvable under high-contrast viewing conditions. Another visual psychophysical parameter is contrast sensitivity (CS), which measures the minimum contrast required for detection of targets over a range of spatial frequencies, and may evaluate visual mechanisms that do not directly subserve acuity. We used the visual evoked potential (VEP) to measure CS in a population of normal subjects and in patients with ophthalmic conditions affecting retinal function, including one patient with a laser injury in the macula. In this patient, the acuity had recovered from

Image enhancement by non-linear extrapolation in frequency space

NASA Technical Reports Server (NTRS)

Anderson, Charles H. (Inventor); Greenspan, Hayit K. (Inventor)

1998-01-01

An input image is enhanced to include spatial frequency components having frequencies higher than those in an input image. To this end, an edge map is generated from the input image using a high band pass filtering technique. An enhancing map is subsequently generated from the edge map, with the enhanced map having spatial frequencies exceeding an initial maximum spatial frequency of the input image. The enhanced map is generated by applying a non-linear operator to the edge map in a manner which preserves the phase transitions of the edges of the input image. The enhanced map is added to the input image to achieve a resulting image having spatial frequencies greater than those in the input image. Simplicity of computations and ease of implementation allow for image sharpening after enlargement and for real-time applications such as videophones, advanced definition television, zooming, and restoration of old motion pictures.

Monitoring evolution of HIFU-induced lesions with backscattered ultrasound

NASA Astrophysics Data System (ADS)

Anand, Ajay; Kaczkowski, Peter J.

2003-04-01

Backscattered radio frequency (rf) data from a modified commercial ultrasound scanner were collected in a series of in vitro experiments in which high intensity focused ultrasound (HIFU) was used to create lesions in freshly excised bovine liver tissue. Two signal processing approaches were used to visualize the temporal evolution of lesion formation. First, apparent tissue motion due to temperature rise was detected using cross-correlation techniques. Results indicate that differential processing of travel time can provide temperature change information throughout the therapy delivery phase and after HIFU has been turned off, over a relatively large spatial region. Second, changes in the frequency spectrum of rf echoes due to changes in the scattering properties of the heated region were observed well before the appearance of hyper-echogenic spots in the focal zone. Furthermore, the increase in attenuation in the lesion zone changes the measured backscatter spectrum from regions distal to it along the imaging beam. Both effects were visualized using spectral processing and display techniques that provide a color spatial map of these features for the clinician. Our results demonstrate potential for these ultrasound-based techniques in targeting and monitoring of HIFU therapy, and perhaps post-treatment visualization of HIFU-induced lesions.

Uncomfortable images in art and nature.

PubMed

Fernandez, Dominic; Wilkins, Arnold J

2008-01-01

The ratings of discomfort from a wide variety of images can be predicted from the energy at different spatial scales in the image, as measured by the Fourier amplitude spectrum of the luminance. Whereas comfortable images show the regression of Fourier amplitude against spatial frequency common in natural scenes, uncomfortable images show a regression with disproportionately greater amplitude at spatial frequencies within two octaves of 3 cycles deg(-1). In six studies, the amplitude in this spatial frequency range relative to that elsewhere in the spectrum explains variance in judgments of discomfort from art, from images constructed from filtered noise, and from art in which the phase or amplitude spectra have been altered. Striped patterns with spatial frequency within the above range are known to be uncomfortable and capable of provoking headaches and seizures in susceptible persons. The present findings show for the first time that, even in more complex images, the energy in this spatial-frequency range is associated with aversion. We propose a simple measurement that can predict aversion to those works of art that have reached the national media because of negative public reaction.

Uncomfortable images in art and nature

PubMed Central

Fernandez, Dominic; Wilkins, Arnold J.

2008-01-01

We find that the ratings of discomfort from a wide variety of images can be predicted from the energy at different spatial scales in the image, as measured by the Fourier amplitude spectrum of the luminance. Whereas comfortable images show the regression of Fourier amplitude against spatial frequency common in natural scenes, uncomfortable images show a regression with disproportionately greater amplitude at spatial frequencies within two octaves of 3 cycles per degree. In six studies, the amplitude at this spatial frequency relative to that 3 octaves below explains variance in judgments of discomfort from art, from images constructed from filtered noise and from art in which the phase or amplitude spectra have been altered. Striped patterns with spatial frequency within the above range are known to be uncomfortable and capable of provoking headaches and seizures in susceptible persons. The present findings show for the first time that even in more complex images the energy in this spatial frequency range is associated with aversion. We propose a simple measurement that can predict aversion to those works of art that have reached the national media because of negative public reaction. PMID:18773732

Pitch perception deficits in nonverbal learning disability.

PubMed

Fernández-Prieto, I; Caprile, C; Tinoco-González, D; Ristol-Orriols, B; López-Sala, A; Póo-Argüelles, P; Pons, F; Navarra, J

2016-12-01

The nonverbal learning disability (NLD) is a neurological dysfunction that affects cognitive functions predominantly related to the right hemisphere such as spatial and abstract reasoning. Previous evidence in healthy adults suggests that acoustic pitch (i.e., the relative difference in frequency between sounds) is, under certain conditions, encoded in specific areas of the right hemisphere that also encode the spatial elevation of external objects (e.g., high vs. low position). Taking this evidence into account, we explored the perception of pitch in preadolescents and adolescents with NLD and in a group of healthy participants matched by age, gender, musical knowledge and handedness. Participants performed four speeded tests: a stimulus detection test and three perceptual categorization tests based on colour, spatial position and pitch. Results revealed that both groups were equally fast at detecting visual targets and categorizing visual stimuli according to their colour. In contrast, the NLD group showed slower responses than the control group when categorizing space (direction of a visual object) and pitch (direction of a change in sound frequency). This pattern of results suggests the presence of a subtle deficit at judging pitch in NLD along with the traditionally-described difficulties in spatial processing. Copyright © 2016. Published by Elsevier Ltd.

Subband/Transform MATLAB Functions For Processing Images

NASA Technical Reports Server (NTRS)

Glover, D.

1995-01-01

SUBTRANS software is package of routines implementing image-data-processing functions for use with MATLAB*(TM) software. Provides capability to transform image data with block transforms and to produce spatial-frequency subbands of transformed data. Functions cascaded to provide further decomposition into more subbands. Also used in image-data-compression systems. For example, transforms used to prepare data for lossy compression. Written for use in MATLAB mathematical-analysis environment.

Structural organization of process zones in upland watersheds of central Nevada and its influence on basin connectivity, dynamics, and wet meadow complexes

Treesearch

Jerry R. Miller; Mark L. Lord; Lionel F. Villarroel; Dru Germanoski; Jeanne C. Chambers

2012-01-01

The drainage network within upland watersheds in central Nevada can be subdivided into distinct zones each dominated by a unique set of processes on the basis of valley form, the geological materials that comprise the valley floor, and the presence or absence of surficial channels. On hillslopes, the type and structure (frequency, length, and spatial arrangement) of...

Algorithm for automatic image dodging of unmanned aerial vehicle images using two-dimensional radiometric spatial attributes

NASA Astrophysics Data System (ADS)

Li, Wenzhuo; Sun, Kaimin; Li, Deren; Bai, Ting

2016-07-01

Unmanned aerial vehicle (UAV) remote sensing technology has come into wide use in recent years. The poor stability of the UAV platform, however, produces more inconsistencies in hue and illumination among UAV images than other more stable platforms. Image dodging is a process used to reduce these inconsistencies caused by different imaging conditions. We propose an algorithm for automatic image dodging of UAV images using two-dimensional radiometric spatial attributes. We use object-level image smoothing to smooth foreground objects in images and acquire an overall reference background image by relative radiometric correction. We apply the Contourlet transform to separate high- and low-frequency sections for every single image, and replace the low-frequency section with the low-frequency section extracted from the corresponding region in the overall reference background image. We apply the inverse Contourlet transform to reconstruct the final dodged images. In this process, a single image must be split into reasonable block sizes with overlaps due to large pixel size. Experimental mosaic results show that our proposed method reduces the uneven distribution of hue and illumination. Moreover, it effectively eliminates dark-bright interstrip effects caused by shadows and vignetting in UAV images while maximally protecting image texture information.

The impact of variation in low-frequency interaural cross correlation on auditory spatial imagery in stereophonic loudspeaker reproduction

NASA Astrophysics Data System (ADS)

Martens, William

2005-04-01

Several attributes of auditory spatial imagery associated with stereophonic sound reproduction are strongly modulated by variation in interaural cross correlation (IACC) within low frequency bands. Nonetheless, a standard practice in bass management for two-channel and multichannel loudspeaker reproduction is to mix low-frequency musical content to a single channel for reproduction via a single driver (e.g., a subwoofer). This paper reviews the results of psychoacoustic studies which support the conclusion that reproduction via multiple drivers of decorrelated low-frequency signals significantly affects such important spatial attributes as auditory source width (ASW), auditory source distance (ASD), and listener envelopment (LEV). A variety of methods have been employed in these tests, including forced choice discrimination and identification, and direct ratings of both global dissimilarity and distinct attributes. Contrary to assumptions that underlie industrial standards established in 1994 by ITU-R. Recommendation BS.775-1, these findings imply that substantial stereophonic spatial information exists within audio signals at frequencies below the 80 to 120 Hz range of prescribed subwoofer cutoff frequencies, and that loudspeaker reproduction of decorrelated signals at frequencies as low as 50 Hz can have an impact upon auditory spatial imagery. [Work supported by VRQ.

Early deficits in spatial memory and theta rhythm in experimental temporal lobe epilepsy.

PubMed

Chauvière, Laetitia; Rafrafi, Nadia; Thinus-Blanc, Catherine; Bartolomei, Fabrice; Esclapez, Monique; Bernard, Christophe

2009-04-29

Patients with temporal lobe epilepsy (TLE), the most common form of epilepsy in adults, often display cognitive deficits. The time course and underlying mechanisms of cognitive decline remain unknown during epileptogenesis (the process leading to epilepsy). Using the rat pilocarpine model of TLE, we performed a longitudinal study to assess spatial and nonspatial cognitive performance during epileptogenesis. In parallel, we monitored interictal-like activity (ILA) in the hippocampal CA1 region, as well as theta oscillations, a brain rhythm central to numerous cognitive processes. Here, we report that spatial memory was altered soon after pilocarpine-induced status epilepticus, i.e., already during the seizure-free, latent period. Spatial deficits correlated with a decrease in the power of theta oscillations but not with the frequency of ILA. Spatial deficits persisted when animals had spontaneous seizures (chronic stage) without further modification. In contrast, nonspatial memory performances remained unaffected throughout. We conclude that the reorganization of hippocampal circuitry that immediately follows the initial insult can affect theta oscillation mechanisms, in turn, resulting in deficits in hippocampus-dependent memory tasks. These deficits may be dissociated from the process that leads to epilepsy itself but could instead constitute, as ILA, early markers in at-risk patients and/or provide beneficial therapeutic targets.

Implications of recurrent disturbance for genetic diversity.

PubMed

Davies, Ian D; Cary, Geoffrey J; Landguth, Erin L; Lindenmayer, David B; Banks, Sam C

2016-02-01

Exploring interactions between ecological disturbance, species' abundances and community composition provides critical insights for ecological dynamics. While disturbance is also potentially an important driver of landscape genetic patterns, the mechanisms by which these patterns may arise by selective and neutral processes are not well-understood. We used simulation to evaluate the relative importance of disturbance regime components, and their interaction with demographic and dispersal processes, on the distribution of genetic diversity across landscapes. We investigated genetic impacts of variation in key components of disturbance regimes and spatial patterns that are likely to respond to climate change and land management, including disturbance size, frequency, and severity. The influence of disturbance was mediated by dispersal distance and, to a limited extent, by birth rate. Nevertheless, all three disturbance regime components strongly influenced spatial and temporal patterns of genetic diversity within subpopulations, and were associated with changes in genetic structure. Furthermore, disturbance-induced changes in temporal population dynamics and the spatial distribution of populations across the landscape resulted in disrupted isolation by distance patterns among populations. Our results show that forecast changes in disturbance regimes have the potential to cause major changes to the distribution of genetic diversity within and among populations. We highlight likely scenarios under which future changes to disturbance size, severity, or frequency will have the strongest impacts on population genetic patterns. In addition, our results have implications for the inference of biological processes from genetic data, because the effects of dispersal on genetic patterns were strongly mediated by disturbance regimes.

Multibeam single frequency synthetic aperture radar processor for imaging separate range swaths

NASA Technical Reports Server (NTRS)

Jain, A. (Inventor)

1982-01-01

A single-frequency multibeam synthetic aperture radar for large swath imaging is disclosed. Each beam illuminates a separate ""footprint'' (i.e., range and azimuth interval). The distinct azimuth intervals for the separate beams produce a distinct Doppler frequency spectrum for each beam. After range correlation of raw data, an optical processor develops image data for the different beams by spatially separating the beams to place each beam of different Doppler frequency spectrum in a different location in the frequency plane as well as the imaging plane of the optical processor. Selection of a beam for imaging may be made in the frequency plane by adjusting the position of an aperture, or in the image plane by adjusting the position of a slit. The raw data may also be processed in digital form in an analogous manner.

Enhancing resolution and contrast in second-harmonic generation microscopy using an advanced maximum likelihood estimation restoration method

NASA Astrophysics Data System (ADS)

Sivaguru, Mayandi; Kabir, Mohammad M.; Gartia, Manas Ranjan; Biggs, David S. C.; Sivaguru, Barghav S.; Sivaguru, Vignesh A.; Berent, Zachary T.; Wagoner Johnson, Amy J.; Fried, Glenn A.; Liu, Gang Logan; Sadayappan, Sakthivel; Toussaint, Kimani C.

2017-02-01

Second-harmonic generation (SHG) microscopy is a label-free imaging technique to study collagenous materials in extracellular matrix environment with high resolution and contrast. However, like many other microscopy techniques, the actual spatial resolution achievable by SHG microscopy is reduced by out-of-focus blur and optical aberrations that degrade particularly the amplitude of the detectable higher spatial frequencies. Being a two-photon scattering process, it is challenging to define a point spread function (PSF) for the SHG imaging modality. As a result, in comparison with other two-photon imaging systems like two-photon fluorescence, it is difficult to apply any PSF-engineering techniques to enhance the experimental spatial resolution closer to the diffraction limit. Here, we present a method to improve the spatial resolution in SHG microscopy using an advanced maximum likelihood estimation (AdvMLE) algorithm to recover the otherwise degraded higher spatial frequencies in an SHG image. Through adaptation and iteration, the AdvMLE algorithm calculates an improved PSF for an SHG image and enhances the spatial resolution by decreasing the full-width-at-halfmaximum (FWHM) by 20%. Similar results are consistently observed for biological tissues with varying SHG sources, such as gold nanoparticles and collagen in porcine feet tendons. By obtaining an experimental transverse spatial resolution of 400 nm, we show that the AdvMLE algorithm brings the practical spatial resolution closer to the theoretical diffraction limit. Our approach is suitable for adaptation in micro-nano CT and MRI imaging, which has the potential to impact diagnosis and treatment of human diseases.

High-speed limnology: using advanced sensors to investigate spatial variability in biogeochemistry and hydrology.

PubMed

Crawford, John T; Loken, Luke C; Casson, Nora J; Smith, Colin; Stone, Amanda G; Winslow, Luke A

2015-01-06

Advanced sensor technology is widely used in aquatic monitoring and research. Most applications focus on temporal variability, whereas spatial variability has been challenging to document. We assess the capability of water chemistry sensors embedded in a high-speed water intake system to document spatial variability. This new sensor platform continuously samples surface water at a range of speeds (0 to >45 km h(-1)) resulting in high-density, mesoscale spatial data. These novel observations reveal previously unknown variability in physical, chemical, and biological factors in streams, rivers, and lakes. By combining multiple sensors into one platform, we were able to detect terrestrial-aquatic hydrologic connections in a small dystrophic lake, to infer the role of main-channel vs backwater nutrient processing in a large river and to detect sharp chemical changes across aquatic ecosystem boundaries in a stream/lake complex. Spatial sensor data were verified in our examples by comparing with standard lab-based measurements of selected variables. Spatial fDOM data showed strong correlation with wet chemistry measurements of DOC, and optical NO3 concentrations were highly correlated with lab-based measurements. High-frequency spatial data similar to our examples could be used to further understand aquatic biogeochemical fluxes, ecological patterns, and ecosystem processes, and will both inform and benefit from fixed-site data.

High-speed limnology: Using advanced sensors to investigate spatial variability in biogeochemistry and hydrology

USGS Publications Warehouse

Crawford, John T.; Loken, Luke C.; Casson, Nora J.; Smith, Collin; Stone, Amanda G.; Winslow, Luke A.

2015-01-01

Advanced sensor technology is widely used in aquatic monitoring and research. Most applications focus on temporal variability, whereas spatial variability has been challenging to document. We assess the capability of water chemistry sensors embedded in a high-speed water intake system to document spatial variability. This new sensor platform continuously samples surface water at a range of speeds (0 to >45 km h–1) resulting in high-density, mesoscale spatial data. These novel observations reveal previously unknown variability in physical, chemical, and biological factors in streams, rivers, and lakes. By combining multiple sensors into one platform, we were able to detect terrestrial–aquatic hydrologic connections in a small dystrophic lake, to infer the role of main-channel vs backwater nutrient processing in a large river and to detect sharp chemical changes across aquatic ecosystem boundaries in a stream/lake complex. Spatial sensor data were verified in our examples by comparing with standard lab-based measurements of selected variables. Spatial fDOM data showed strong correlation with wet chemistry measurements of DOC, and optical NO3 concentrations were highly correlated with lab-based measurements. High-frequency spatial data similar to our examples could be used to further understand aquatic biogeochemical fluxes, ecological patterns, and ecosystem processes, and will both inform and benefit from fixed-site data.

What Do They Have in Common? Drivers of Streamflow Spatial Correlation and Prediction of Flow Regimes in Ungauged Locations

NASA Astrophysics Data System (ADS)

Betterle, A.; Radny, D.; Schirmer, M.; Botter, G.

2017-12-01

The spatial correlation of daily streamflows represents a statistical index encapsulating the similarity between hydrographs at two arbitrary catchment outlets. In this work, a process-based analytical framework is utilized to investigate the hydrological drivers of streamflow spatial correlation through an extensive application to 78 pairs of stream gauges belonging to 13 unregulated catchments in the eastern United States. The analysis provides insight on how the observed heterogeneity of the physical processes that control flow dynamics ultimately affect streamflow correlation and spatial patterns of flow regimes. Despite the variability of recession properties across the study catchments, the impact of heterogeneous drainage rates on the streamflow spatial correlation is overwhelmed by the spatial variability of frequency and intensity of effective rainfall events. Overall, model performances are satisfactory, with root mean square errors between modeled and observed streamflow spatial correlation below 10% in most cases. We also propose a method for estimating streamflow correlation in the absence of discharge data, which proves useful to predict streamflow regimes in ungauged areas. The method consists in setting a minimum threshold on the modeled flow correlation to individuate hydrologically similar sites. Catchment outlets that are most correlated (ρ>0.9) are found to be characterized by analogous streamflow distributions across a broad range of flow regimes.

Wide-field high spatial frequency domain imaging of tissue microstructure

NASA Astrophysics Data System (ADS)

Lin, Weihao; Zeng, Bixin; Cao, Zili; Zhu, Danfeng; Xu, M.

2018-02-01

Wide-field tissue imaging is usually not capable of resolving tissue microstructure. We present High Spatial Frequency Domain Imaging (HSFDI) - a noncontact imaging modality that spatially maps the tissue microscopic scattering structures over a large field of view. Based on an analytical reflectance model of sub-diffusive light from forward-peaked highly scattering media, HSFDI quantifies the spatially-resolved parameters of the light scattering phase function from the reflectance of structured light modulated at high spatial frequencies. We have demonstrated with ex vivo cancerous tissue to validate the robustness of HSFDI in significant contrast and differentiation of the microstructutral parameters between different types and disease states of tissue.

Captured by the pain: pain steady-state evoked potentials are not modulated by selective spatial attention.

PubMed

Blöchl, Maria; Franz, Marcel; Miltner, Wolfgang H R; Weiss, Thomas

2015-04-07

Attention has been shown to affect the neural processing of pain. However, the exact mechanisms underlying this modulation remain unknown. Here, we used a new method called pain steady-state evoked potentials (PSSEPs) to investigate whether selective spatial attention affects EEG responses to tonic painful stimuli. In general, steady-state evoked potentials reflect changes in the EEG spectrum at a certain frequency that correspond to the frequency of a train of applied stimuli. In this study, high intensity transcutaneous electrical stimulation was delivered to both hands simultaneously with 31 Hz and 37 Hz, respectively. Subject׳s attention was directed to one of the two trains of stimulation in order to detect a small gap that was occasionally interspersed into the stimulus trains. Thereby, they had to ignore the stimulation applied to the other hand. Results show that PSSEPs were induced at 31 Hz and 37 Hz at frontal and central electrodes. PSSEPs occurred contralaterally to the respective hand stimulated with that frequency. Surprisingly, the magnitude of PSSEPs was not modulated by spatial attention towards one of the two stimuli. Our results indicate that attention can hardly be shifted between two simultaneously applied tonic painful stimulations. Copyright © 2015 Elsevier B.V. All rights reserved.

A modeling approach for aerosol optical depth analysis during forest fire events

NASA Astrophysics Data System (ADS)

Aube, Martin P.; O'Neill, Normand T.; Royer, Alain; Lavoue, David

2004-10-01

Measurements of aerosol optical depth (AOD) are important indicators of aerosol particle behavior. Up to now the two standard techniques used for retrieving AOD are; (i) sun photometry which provides measurements of high temporal frequency and sparse spatial frequency, and (ii) satellite based approaches such as DDV (Dense Dark Vegetation) based inversion algorithms which yield AOD over dark targets in remotely sensed imagery. Although the latter techniques allow AOD retrieval over appreciable spatial domains, the irregular spatial pattern of dark targets and the typically low repeat frequencies of imaging satellites exclude the acquisition of AOD databases on a continuous spatio-temporal basis. We attempt to fill gaps in spatio-temporal AOD measurements using a new assimilation methodology that links AOD measurements and the predictions of a particulate matter Transport Model. This modelling package (AODSEM V2.0 for Aerosol Optical Depth Spatio-temporal Evolution Model) uses a size and aerosol type segregated semi-Lagrangian trajectory algorithm driven by analysed meteorological data. Its novelty resides in the fact that the model evolution may be tied to both ground based and satellite level AOD measurement and all physical processes have been optimized to track this important and robust parameter. We applied this methodology to a significant smoke event that occurred over the eastern part of North America in July 2002.

Combined multispectral spatial frequency domain imaging and computed tomography system for intraoperative breast tumor margin assessment

NASA Astrophysics Data System (ADS)

McClatchy, D. M.; Rizzo, E. J.; Krishnaswamy, V.; Kanick, S. C.; Wells, W. A.; Paulsen, K. D.; Pogue, B. W.

2017-02-01

There is a dire clinical need for surgical margin guidance in breast conserving therapy (BCT). We present a multispectral spatial frequency domain imaging (SFDI) system, spanning the visible and near-infrared (NIR) wavelengths, combined with a shielded X-ray computed tomography (CT) system, designed for intraoperative breast tumor margin assessment. While the CT can provide a volumetric visualization of the tumor core and its spiculations, the co-registered SFDI can provide superficial and quantitative information about localized changes tissue morphology from light scattering parameters. These light scattering parameters include both model-based parameters of sub-diffusive light scattering related to the particle size scale distribution and also textural information of the high spatial frequency reflectance. Because the SFDI and CT components are rigidly fixed, a simple transformation can be used to simultaneously display the SFDI and CT data in the same coordinate system. This is achieved through the Visualization Toolkit (vtk) file format in the open-source Slicer medical imaging software package. In this manuscript, the instrumentation, data processing, and preliminary human specimen data will be presented. The ultimate goal of this work is to evaluate this technology in a prospective clinical trial, and the current limitations and engineering solutions to meet this goal will also be discussed.

Compact sub-kilohertz low-frequency quantum light source based on four-wave mixing in cesium vapor

NASA Astrophysics Data System (ADS)

Ma, Rong; Liu, Wei; Qin, Zhongzhong; Su, Xiaolong; Jia, Xiaojun; Zhang, Junxiang; Gao, Jiangrui

2018-03-01

Using a nondegenerate four-wave mixing (FWM) process based on a double-{\\Lambda} scheme in hot cesium vapor, we demonstrate a compact diode-laser-pumped quantum light source for the generation of quantum correlated twin beams with a maximum squeezing of 6.5 dB. The squeezing is observed at a Fourier frequency in the audio band down to 0.7 kHz which, to the best of our knowledge, is the first observation of sub-kilohertz intensity-difference squeezing in an atomic system so far. A phase-matching condition is also investigated in our system, which confirms the spatial-multi-mode characteristics of the FWM process. Our compact low-frequency squeezed light source may find applications in quantum imaging, quantum metrology, and the transfer of optical squeezing onto a matter wave.

Composite Characterization Using Laser Doppler Vibrometry and Multi-Frequency Wavenumber Analysis

NASA Technical Reports Server (NTRS)

Juarez, Peter; Leckey, Cara

2015-01-01

NASA has recognized the need for better characterization of composite materials to support advances in aeronautics and the next generation of space exploration vehicles. An area of related research is the evaluation of impact induced delaminations. Presented is a non-contact method of measuring the ply depth of impact delamination damage in a composite through use of a Scanning Laser Doppler Vibrometer (SLDV), multi-frequency wavenumber analysis, and a wavenumber-ply correlation algorithm. A single acquisition of a chirp excited lamb wavefield in an impacted composite is post-processed into a numerous single frequency excitation wavefields through a deconvolution process. A spatially windowed wavenumber analysis then extracts local wavenumbers from the wavefield, which are then correlated to theoretical dispersion curves for ply depth determination. SLDV based methods to characterize as-manufactured composite variation using wavefield analysis will also be discussed.

Space shuttle electromagnetic environment experiment. Phase A: Definition study

NASA Technical Reports Server (NTRS)

Haber, F.; Showers, R. M.; Taheri, S. H.; Forrest, L. A., Jr.; Kocher, C.

1974-01-01

A program is discussed which develops a concept for measuring the electromagnetic environment on earth with equipment on board an orbiting space shuttle. Earlier work on spaceborne measuring experiments is reviewed, and emissions to be expected are estimated using, in part, previously gathered data. General relations among system parameters are presented, followed by a proposal on spatial and frequency scanning concepts. The methods proposed include a nadir looking measurement with small lateral scan and a circularly scanned measurement looking tangent to the earth's surface at the horizon. Antenna requirements are given, assuming frequency coverage from 400 MHz to 40 GHz. For the low frequency range, 400-1000 MHz, a processed, thinned array is proposed which will be more fully analyzed in the next phase of the program. Preliminary hardware and data processing requirements are presented.

Spatial processing in the auditory cortex of the macaque monkey

NASA Astrophysics Data System (ADS)

Recanzone, Gregg H.

2000-10-01

The patterns of cortico-cortical and cortico-thalamic connections of auditory cortical areas in the rhesus monkey have led to the hypothesis that acoustic information is processed in series and in parallel in the primate auditory cortex. Recent physiological experiments in the behaving monkey indicate that the response properties of neurons in different cortical areas are both functionally distinct from each other, which is indicative of parallel processing, and functionally similar to each other, which is indicative of serial processing. Thus, auditory cortical processing may be similar to the serial and parallel "what" and "where" processing by the primate visual cortex. If "where" information is serially processed in the primate auditory cortex, neurons in cortical areas along this pathway should have progressively better spatial tuning properties. This prediction is supported by recent experiments that have shown that neurons in the caudomedial field have better spatial tuning properties than neurons in the primary auditory cortex. Neurons in the caudomedial field are also better than primary auditory cortex neurons at predicting the sound localization ability across different stimulus frequencies and bandwidths in both azimuth and elevation. These data support the hypothesis that the primate auditory cortex processes acoustic information in a serial and parallel manner and suggest that this may be a general cortical mechanism for sensory perception.

Periodic density modulation for quasi-phase-matching of optical frequency conversion is inefficient under shallow focusing and constant ambient pressure.

PubMed

Hadas, Itai; Bahabad, Alon

2016-09-01

The two main mechanisms of a periodic density modulation relevant to nonlinear optical conversion in a gas medium are spatial modulations of the index of refraction and of the number of emitters. For a one-dimensional model neglecting focusing and using a constant ambient pressure, it is shown theoretically and demonstrated numerically that the effects of these two mechanisms during frequency conversion cancel each other exactly. Under the considered conditions, this makes density modulation inefficient for quasi-phase-matching an optical frequency conversion process. This result is particularly relevant for high-order harmonic generation.

Spatial and temporal patterns of bank failure during extreme flood events: Evidence of nonlinearity and self-organised criticality at the basin scale?

NASA Astrophysics Data System (ADS)

Thompson, C. J.; Croke, J. C.; Grove, J. R.

2012-04-01

Non-linearity in physical systems provides a conceptual framework to explain complex patterns and form that are derived from complex internal dynamics rather than external forcings, and can be used to inform modeling and improve landscape management. One process that has been investigated previously to explore the existence of self-organised critical system (SOC) in river systems at the basin-scale is bank failure. Spatial trends in bank failure have been previously quantified to determine if the distribution of bank failures at the basin scale exhibit the necessary power law magnitude/frequency distributions. More commonly bank failures are investigated at a small-scale using several cross-sections with strong emphasis on local-scale factors such as bank height, cohesion and hydraulic properties. Advancing our understanding of non-linearity in such processes, however, requires many more studies where both the spatial and temporal measurements of the process can be used to investigate the existence or otherwise of non-linearity and self-organised criticality. This study presents measurements of bank failure throughout the Lockyer catchment in southeast Queensland, Australia, which experienced an extreme flood event in January 2011 resulting in the loss of human lives and geomorphic channel change. The most dominant form of fluvial adjustment consisted of changes in channel geometry and notably widespread bank failures, which were readily identifiable as 'scalloped' shaped failure scarps. The spatial extents of these were mapped using high-resolution LiDAR derived digital elevation model and were verified by field surveys and air photos. Pre-flood event LiDAR coverage for the catchment also existed allowing direct comparison of the magnitude and frequency of bank failures from both pre and post-flood time periods. Data were collected and analysed within a GIS framework and investigated for power-law relationships. Bank failures appeared random and occurred throughout the basin but plots of magnitude and frequency did display power-law scaling of failures. In addition, there was a lack of site specific correlations between bank failure and other factors such channel width, bank height and stream power. The data are used here to discuss the existence of SOC in fluvial systems and the relative role of local and basin-wide processes in influencing their distribution in space and time.

Phase Coupling in Langmuir Wave Packets: Evidence for Four Wave Interactions in Solar Type III Radio Bursts

NASA Technical Reports Server (NTRS)

Thejappa, G.; MacDowall, R. J.; Bergamo, M.

2012-01-01

The four wave interaction process, known as the oscillating two stream instability (OTSI) is considered as one of the mechanisms responsible for stabilizing the electron beams associated with solar type III radio bursts. It has been reported that (1) an intense localized Langmuir wave packet associated with a type III burst contains the spectral characteristics of the OTSI: (a) a resonant peak at the local electron plasma frequency, f(sub pe), (b) a Stokes peak at a frequency slightly lower than f(sub pe), (c) anti-Stokes peak at a frequency slightly higher than f(sub pe), and (d) a low frequency enhancement below a few hundred Hz, (2) the frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI, and (3) the peak intensity of the wave packet is well above the thresholds for the OTSI as well as spatial collapse of envelope solitons. Here, for the first time, applying the trispectral analysis on this wave packet, we show that the tricoherence, which measures the degree of coherent four-wave coupling amongst the observed spectral components exhibits a peak. This provides an additional evidence for the OTSI and related spatial collapse of Langmuir envelope solitons in type III burst sources.

Multidimensional analysis of the abnormal neural oscillations associated with lexical processing in schizophrenia.

PubMed

Xu, Tingting; Stephane, Massoud; Parhi, Keshab K

2013-04-01

The neural mechanisms of language abnormalities, the core symptoms in schizophrenia, remain unclear. In this study, a new experimental paradigm, combining magnetoencephalography (MEG) techniques and machine intelligence methodologies, was designed to gain knowledge about the frequency, brain location, and time of occurrence of the neural oscillations that are associated with lexical processing in schizophrenia. The 248-channel MEG recordings were obtained from 12 patients with schizophrenia and 10 healthy controls, during a lexical processing task, where the patients discriminated correct from incorrect lexical stimuli that were visually presented. Event-related desynchronization/synchronization (ERD/ERS) was computed along the frequency, time, and space dimensions combined, that resulted in a large spectral-spatial-temporal ERD/ERS feature set. Machine intelligence techniques were then applied to select a small subset of oscillation patterns that are abnormal in patients with schizophrenia, according to their discriminating power in patient and control classification. Patients with schizophrenia showed abnormal ERD/ERS patterns during both lexical encoding and post-encoding periods. The top-ranked features were located at the occipital and left frontal-temporal areas, and covered a wide frequency range, including δ (1-4 Hz), α (8-12 Hz), β (12-32 Hz), and γ (32-48 Hz) bands. These top features could discriminate the patient group from the control group with 90.91% high accuracy, which demonstrates significant brain oscillation abnormalities in patients with schizophrenia at the specific frequency, time, and brain location indicated by these top features. As neural oscillation abnormality may be due to the mechanisms of the disease, the spectral, spatial, and temporal content of the discriminating features can offer useful information for helping understand the physiological basis of the language disorder in schizophrenia, as well as the pathology of the disease itself.

Comparing the minimum spatial-frequency content for recognizing Chinese and alphabet characters

PubMed Central

Wang, Hui; Legge, Gordon E.

2018-01-01

Visual blur is a common problem that causes difficulty in pattern recognition for normally sighted people under degraded viewing conditions (e.g., near the acuity limit, when defocused, or in fog) and also for people with impaired vision. For reliable identification, the spatial frequency content of an object needs to extend up to or exceed a minimum value in units of cycles per object, referred to as the critical spatial frequency. In this study, we investigated the critical spatial frequency for alphabet and Chinese characters, and examined the effect of pattern complexity. The stimuli were divided into seven categories based on their perimetric complexity, including the lowercase and uppercase alphabet letters, and five groups of Chinese characters. We found that the critical spatial frequency significantly increased with complexity, from 1.01 cycles per character for the simplest group to 2.00 cycles per character for the most complex group of Chinese characters. A second goal of the study was to test a space-bandwidth invariance hypothesis that would represent a tradeoff between the critical spatial frequency and the number of adjacent patterns that can be recognized at one time. We tested this hypothesis by comparing the critical spatial frequencies in cycles per character from the current study and visual-span sizes in number of characters (measured by Wang, He, & Legge, 2014) for sets of characters with different complexities. For the character size (1.2°) we used in the study, we found an invariant product of approximately 10 cycles, which may represent a capacity limitation on visual pattern recognition. PMID:29297056

Solid perception mechanism by a shading pattern: spatial frequency components in a corrugated wave pattern.

PubMed

Nameda, N

1988-01-01

Illumination allows solid object perception to be obtained and depicted by a shading pattern produced by lighting. The shading cue, as one of solid perception cues (Gibson 1979), was investigated in regard to a white corrugated wave shape, using computer graphic device: Tospix-2. The reason the corrugated wave was chosen, is that an alternately bright and dark pattern, produced by shading, can be conveniently analyzed into contained spatial frequencies. This paper reports spatial frequency properties contained in the shading pattern. The shading patterns, input into the computer graphic device, are analyzed by Fourier Transformation by the same device. After the filtration by various spatial frequency low and high pass filters, Inverse Fourier Transformation is carried out for the residual components. The result of the analysis indicates that the third through higher harmonics components are important in regard to presenting a solid reality feeling in solid perception. Sakata (1983) also reported that an edged pattern, superimposed onto a lower sinusoidal pattern, was important in solid perception. The third through higher harmonics components express the changing position of luminance on the pattern, and a slanted plane relating to the light direction. Detection of a solid shape, constructed with flat planes, is assumed to be on the bottom of the perfect curved solid perception mechanism. Apparent evidence for this assumption, in difficult visual conditions, is that a flat paneled solid is seen before the curved solid. This mechanism is explained by two spatial frequency neural network systems, assumed as having correspondence with higher spatial frequency detection and lower spatial frequency detection.

Mapping Frequency-Specific Tone Predictions in the Human Auditory Cortex at High Spatial Resolution.

PubMed

Berlot, Eva; Formisano, Elia; De Martino, Federico

2018-05-23

Auditory inputs reaching our ears are often incomplete, but our brains nevertheless transform them into rich and complete perceptual phenomena such as meaningful conversations or pleasurable music. It has been hypothesized that our brains extract regularities in inputs, which enables us to predict the upcoming stimuli, leading to efficient sensory processing. However, it is unclear whether tone predictions are encoded with similar specificity as perceived signals. Here, we used high-field fMRI to investigate whether human auditory regions encode one of the most defining characteristics of auditory perception: the frequency of predicted tones. Two pairs of tone sequences were presented in ascending or descending directions, with the last tone omitted in half of the trials. Every pair of incomplete sequences contained identical sounds, but was associated with different expectations about the last tone (a high- or low-frequency target). This allowed us to disambiguate predictive signaling from sensory-driven processing. We recorded fMRI responses from eight female participants during passive listening to complete and incomplete sequences. Inspection of specificity and spatial patterns of responses revealed that target frequencies were encoded similarly during their presentations, as well as during omissions, suggesting frequency-specific encoding of predicted tones in the auditory cortex (AC). Importantly, frequency specificity of predictive signaling was observed already at the earliest levels of auditory cortical hierarchy: in the primary AC. Our findings provide evidence for content-specific predictive processing starting at the earliest cortical levels. SIGNIFICANCE STATEMENT Given the abundance of sensory information around us in any given moment, it has been proposed that our brain uses contextual information to prioritize and form predictions about incoming signals. However, there remains a surprising lack of understanding of the specificity and content of such prediction signaling; for example, whether a predicted tone is encoded with similar specificity as a perceived tone. Here, we show that early auditory regions encode the frequency of a tone that is predicted yet omitted. Our findings contribute to the understanding of how expectations shape sound processing in the human auditory cortex and provide further insights into how contextual information influences computations in neuronal circuits. Copyright © 2018 the authors 0270-6474/18/384934-09$15.00/0.

Auditory rehabilitation after stroke: treatment of auditory processing disorders in stroke patients with personal frequency-modulated (FM) systems.

PubMed

Koohi, Nehzat; Vickers, Deborah; Chandrashekar, Hoskote; Tsang, Benjamin; Werring, David; Bamiou, Doris-Eva

2017-03-01

Auditory disability due to impaired auditory processing (AP) despite normal pure-tone thresholds is common after stroke, and it leads to isolation, reduced quality of life and physical decline. There are currently no proven remedial interventions for AP deficits in stroke patients. This is the first study to investigate the benefits of personal frequency-modulated (FM) systems in stroke patients with disordered AP. Fifty stroke patients had baseline audiological assessments, AP tests and completed the (modified) Amsterdam Inventory for Auditory Disability and Hearing Handicap Inventory for Elderly questionnaires. Nine out of these 50 patients were diagnosed with disordered AP based on severe deficits in understanding speech in background noise but with normal pure-tone thresholds. These nine patients underwent spatial speech-in-noise testing in a sound-attenuating chamber (the "crescent of sound") with and without FM systems. The signal-to-noise ratio (SNR) for 50% correct speech recognition performance was measured with speech presented from 0° azimuth and competing babble from ±90° azimuth. Spatial release from masking (SRM) was defined as the difference between SNRs measured with co-located speech and babble and SNRs measured with spatially separated speech and babble. The SRM significantly improved when babble was spatially separated from target speech, while the patients had the FM systems in their ears compared to without the FM systems. Personal FM systems may substantially improve speech-in-noise deficits in stroke patients who are not eligible for conventional hearing aids. FMs are feasible in stroke patients and show promise to address impaired AP after stroke. Implications for Rehabilitation This is the first study to investigate the benefits of personal frequency-modulated (FM) systems in stroke patients with disordered AP. All cases significantly improved speech perception in noise with the FM systems, when noise was spatially separated from the speech signal by 90° compared with unaided listening. Personal FM systems are feasible in stroke patients, and may be of benefit in just under 20% of this population, who are not eligible for conventional hearing aids.

Multi-frequency electrical impedance tomography as a non-invasive tool to characterize and monitor crop root systems

NASA Astrophysics Data System (ADS)

Weigand, Maximilian; Kemna, Andreas

2017-02-01

A better understanding of root-soil interactions and associated processes is essential in achieving progress in crop breeding and management, prompting the need for high-resolution and non-destructive characterization methods. To date, such methods are still lacking or restricted by technical constraints, in particular the charactization and monitoring of root growth and function in the field. A promising technique in this respect is electrical impedance tomography (EIT), which utilizes low-frequency (< 1 kHz)- electrical conduction- and polarization properties in an imaging framework. It is well established that cells and cell clusters exhibit an electrical polarization response in alternating electric-current fields due to electrical double layers which form at cell membranes. This double layer is directly related to the electrical surface properties of the membrane, which in turn are influenced by nutrient dynamics (fluxes and concentrations on both sides of the membranes). Therefore, it can be assumed that the electrical polarization properties of roots are inherently related to ion uptake and translocation processes in the root systems. We hereby propose broadband (mHz to hundreds of Hz) multi-frequency EIT as a non-invasive methodological approach for the monitoring and physiological, i.e., functional, characterization of crop root systems. The approach combines the spatial-resolution capability of an imaging method with the diagnostic potential of electrical-impedance spectroscopy. The capability of multi-frequency EIT to characterize and monitor crop root systems was investigated in a rhizotron laboratory experiment, in which the root system of oilseed plants was monitored in a water-filled rhizotron, that is, in a nutrient-deprived environment. We found a low-frequency polarization response of the root system, which enabled the successful delineation of its spatial extension. The magnitude of the overall polarization response decreased along with the physiological decay of the root system due to the stress situation. Spectral polarization parameters, as derived from a pixel-based Debye decomposition analysis of the multi-frequency imaging results, reveal systematic changes in the spatial and spectral electrical response of the root system. In particular, quantified mean relaxation times (of the order of 10 ms) indicate changes in the length scales on which the polarization processes took place in the root system, as a response to the prolonged induced stress situation. Our results demonstrate that broadband EIT is a capable, non-invasive method to image root system extension as well as to monitor changes associated with the root physiological processes. Given its applicability on both laboratory and field scales, our results suggest an enormous potential of the method for the structural and functional imaging of root systems for various applications. This particularly holds for the field scale, where corresponding methods are highly desired but to date are lacking.

Cognitive processing of orientation discrimination in anisometropic amblyopia.

PubMed

Wang, Jianglan; Zhao, Jiao; Wang, Shoujing; Gong, Rui; Zheng, Zhong; Liu, Longqian

2017-01-01

Cognition is very important in our daily life. However, amblyopia has abnormal visual cognition. Physiological changes of the brain during processes of cognition could be reflected with ERPs. So the purpose of this study was to investigate the speed and the capacity of resource allocation in visual cognitive processing in orientation discrimination task during monocular and binocular viewing conditions of amblyopia and normal control as well as the corresponding eyes of the two groups with ERPs. We also sought to investigate whether the speed and the capacity of resource allocation in visual cognitive processing vary with target stimuli at different spatial frequencies (3, 6 and 9 cpd) in amblyopia and normal control as well as between the corresponding eyes of the two groups. Fifteen mild to moderate anisometropic amblyopes and ten normal controls were recruited. Three-stimulus oddball paradigms of three different spatial frequency orientation discrimination tasks were used in monocular and binocular conditions in amblyopes and normal controls to elicit event-related potentials (ERPs). Accuracy (ACC), reaction time (RT), the latency of novelty P300 and P3b, and the amplitude of novelty P300 and P3b were measured. Results showed that RT was longer in the amblyopic eye than in both eyes of amblyopia and non-dominant eye in control. Novelty P300 amplitude was largest in the amblyopic eye, followed by the fellow eye, and smallest in both eyes of amblyopia. Novelty P300 amplitude was larger in the amblyopic eye than non-dominant eye and was larger in fellow eye than dominant eye. P3b latency was longer in the amblyopic eye than in the fellow eye, both eyes of amblyopia and non-dominant eye of control. P3b latency was not associated with RT in amblyopia. Neural responses of the amblyopic eye are abnormal at the middle and late stages of cognitive processing, indicating that the amblyopic eye needs to spend more time or integrate more resources to process the same visual task. Fellow eye and both eyes in amblyopia are slightly different from the dominant eye and both eyes in normal control at the middle and late stages of cognitive processing. Meanwhile, abnormal extents of amblyopic eye do not vary with three different spatial frequencies used in our study.

Cognitive processing of orientation discrimination in anisometropic amblyopia

PubMed Central

Wang, Jianglan; Zhao, Jiao; Wang, Shoujing; Gong, Rui; Zheng, Zhong; Liu, Longqian

2017-01-01

Cognition is very important in our daily life. However, amblyopia has abnormal visual cognition. Physiological changes of the brain during processes of cognition could be reflected with ERPs. So the purpose of this study was to investigate the speed and the capacity of resource allocation in visual cognitive processing in orientation discrimination task during monocular and binocular viewing conditions of amblyopia and normal control as well as the corresponding eyes of the two groups with ERPs. We also sought to investigate whether the speed and the capacity of resource allocation in visual cognitive processing vary with target stimuli at different spatial frequencies (3, 6 and 9 cpd) in amblyopia and normal control as well as between the corresponding eyes of the two groups. Fifteen mild to moderate anisometropic amblyopes and ten normal controls were recruited. Three-stimulus oddball paradigms of three different spatial frequency orientation discrimination tasks were used in monocular and binocular conditions in amblyopes and normal controls to elicit event-related potentials (ERPs). Accuracy (ACC), reaction time (RT), the latency of novelty P300 and P3b, and the amplitude of novelty P300 and P3b were measured. Results showed that RT was longer in the amblyopic eye than in both eyes of amblyopia and non-dominant eye in control. Novelty P300 amplitude was largest in the amblyopic eye, followed by the fellow eye, and smallest in both eyes of amblyopia. Novelty P300 amplitude was larger in the amblyopic eye than non-dominant eye and was larger in fellow eye than dominant eye. P3b latency was longer in the amblyopic eye than in the fellow eye, both eyes of amblyopia and non-dominant eye of control. P3b latency was not associated with RT in amblyopia. Neural responses of the amblyopic eye are abnormal at the middle and late stages of cognitive processing, indicating that the amblyopic eye needs to spend more time or integrate more resources to process the same visual task. Fellow eye and both eyes in amblyopia are slightly different from the dominant eye and both eyes in normal control at the middle and late stages of cognitive processing. Meanwhile, abnormal extents of amblyopic eye do not vary with three different spatial frequencies used in our study. PMID:29023501

"Paradox of slow frequencies" - Are slow frequencies in upper cortical layers a neural predisposition of the level/state of consciousness (NPC)?

PubMed

Northoff, Georg

2017-09-01

Consciousness research has much focused on faster frequencies like alpha or gamma while neglecting the slower ones in the infraslow (0.001-0.1Hz) and slow (0.1-1Hz) frequency range. These slower frequency ranges have a "bad reputation" though; their increase in power can observed during the loss of consciousness as in sleep, anesthesia, and vegetative state. However, at the same time, slower frequencies have been conceived instrumental for consciousness. The present paper aims to resolve this paradox which I describe as "paradox of slow frequencies". I first show various data that suggest a central role of slower frequencies in integrating faster ones, i.e., "temporo-spatial integration and nestedness". Such "temporo-spatial integration and nestedness" is disrupted during the loss of consciousness as in anesthesia and sleep leading to "temporo-spatial fragmentation and isolation" between slow and fast frequencies. Slow frequencies are supposedly mediated by neural activity in upper cortical layers in higher-order associative regions as distinguished from lower cortical layers that are related to faster frequencies. Taken together, slower and faster frequencies take on different roles for the level/state of consciousness. Faster frequencies by themselves are sufficient and thus a neural correlate of consciousness (NCC) while slower frequencies are a necessary non-sufficient condition of possible consciousness, e.g., a neural predisposition of the level/state of consciousness (NPC). This resolves the "paradox of slow frequencies" in that it assigns different roles to slower and faster frequencies in consciousness, i.e., NCC and NPC. Taken as NCC and NPC, fast and slow frequencies including their relation as in "temporo-spatial integration and nestedness" can be considered a first "building bloc" of a future "temporo-spatial theory of consciousness" (TTC) (Northoff, 2013; Northoff, 2014b; Northoff & Huang, 2017). Copyright © 2017 Elsevier Inc. All rights reserved.

Real-time object tracking based on scale-invariant features employing bio-inspired hardware.

PubMed

Yasukawa, Shinsuke; Okuno, Hirotsugu; Ishii, Kazuo; Yagi, Tetsuya

2016-09-01

We developed a vision sensor system that performs a scale-invariant feature transform (SIFT) in real time. To apply the SIFT algorithm efficiently, we focus on a two-fold process performed by the visual system: whole-image parallel filtering and frequency-band parallel processing. The vision sensor system comprises an active pixel sensor, a metal-oxide semiconductor (MOS)-based resistive network, a field-programmable gate array (FPGA), and a digital computer. We employed the MOS-based resistive network for instantaneous spatial filtering and a configurable filter size. The FPGA is used to pipeline process the frequency-band signals. The proposed system was evaluated by tracking the feature points detected on an object in a video. Copyright © 2016 Elsevier Ltd. All rights reserved.

Changes in tendon spatial frequency parameters with loading.

PubMed

Pearson, Stephen J; Engel, Aaron J; Bashford, Gregory R

2017-05-24

To examine and compare the loading related changes in micro-morphology of the patellar tendon. Fifteen healthy young males (age 19±3yrs, body mass 83±5kg) were utilised in a within subjects matched pairs design. B mode ultrasound images were taken in the sagittal plane of the patellar tendon at rest with the knee at 90° flexion. Repeat images were taken whilst the subjects were carrying out maximal voluntary isometric contractions. Spatial frequency parameters related to the tendon morphology were determined within regions of interest (ROI) from the B mode images at rest and during isometric contractions. A number of spatial parameters were observed to be significantly different between resting and contracted images (Peak spatial frequency radius (PSFR), axis ratio, spatial Q-factor, PSFR amplitude ratio, and the sum). These spatial frequency parameters were indicative of acute alterations in the tendon micro-morphology with loading. Acute loading modifies the micro-morphology of the tendon, as observed via spatial frequency analysis. Further research is warranted to explore its utility with regard to different loading induced micro-morphological alterations, as these could give valuable insight not only to aid strengthening of this tissue but also optimization of recovery from injury and treatment of conditions such as tendinopathies. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fire regimes, past and present

Treesearch

Carl N. Skinner; Chiru Chang

1996-01-01

Fire has been an important ecosystem process in the Sierra Nevada for thousands of years. Before the area was settled in the 1850s, fires were generally frequent throughout much of the range. The frequency and severity of these fires varied spatially and temporally depending upon climate, elevation, topography, vegetation, edaphic conditions, and human cultural...

Femtosecond laser irradiation on Nd:YAG crystal: Surface ablation and high-spatial-frequency nanograting

NASA Astrophysics Data System (ADS)

Ren, Yingying; Zhang, Limu; Romero, Carolina; Vázquez de Aldana, Javier R.; Chen, Feng

2018-05-01

In this work, we systematically study the surface modifications of femtosecond (fs) laser irradiated Nd:YAG crystal in stationary focusing case (i.e., the beam focused on the target in the steady focusing geometry) or dynamic scanning case (i.e., focused fs-laser beam scanning over the target material). Micro-sized structures (e.g. micro-craters or lines) are experimentally produced in a large scale of parameters in terms of pulse energy as well as (effective) pulse number. Surface ablation of Nd:YAG surface under both processing cases are investigated, involving the morphological evolution, parameter dependence, the ablation threshold fluences and the incubation factors. Meanwhile, under specific irradiation conditions, periodic surface structures with high-spatial-frequency (<λ/2) can be generated. The obtained period is as short as 157 nm in this work. Investigations on the evolution of nanograting formation and fluence dependence of period are performed. The experimental results obtained under different cases and the comparison between them reveal that incubation effect plays an important role not only in the ablation of Nd:YAG surface but also in the processes of nanograting formation.

Optically pre-amplified lidar-radar

NASA Astrophysics Data System (ADS)

Morvan, Loic; Dolfi, Daniel; Huignard, Jean-Pierre

2001-09-01

We present the concept of an optically pre-amplified intensity modulated lidar, where the modulation frequency is in the microwave domain (1-10 GHz). Such a system permits to combine directivity of laser beams with mature radar processing. As an intensity modulated or dual-frequency laser beam is directed on a target, the backscattered intensity is collected by an optical system, pass through an optical preamplifier, and is detected on a high speed photodiode in a direct detection scheme. A radar type processing permits then to extract range, speed and identification information. The association of spatially multimode amplifier and direct detection allows low sensitivity to atmospheric turbulence and large field of view. We demonstrated theoretically that optical pre-amplification can greatly enhance sensitivity, even in spatially multimode amplifiers, such as free-space amplifier or multimode doped fiber. Computed range estimates based on this concept are presented. Laboratory demonstrations using 1 to 3 GHz modulated laser sources and >20 dB gain in multimode amplifiers are detailed. Preliminary experimental results on range and speed measurements and possible use for large amplitude vibrometry will be presented.

Orientation masking and cross-orientation suppression (XOS): implications for estimates of filter bandwidth.

PubMed

Meese, Tim S; Holmes, David J

2010-10-01

Most contemporary models of spatial vision include a cross-oriented route to suppression (masking from a broadly tuned inhibitory pool), which is most potent at low spatial and high temporal frequencies (T. S. Meese & D. J. Holmes, 2007). The influence of this pathway can elevate orientation-masking functions without exciting the target mechanism, and because early psychophysical estimates of filter bandwidth did not accommodate this, it is likely that they have been overestimated for this corner of stimulus space. Here we show that a transient 40% contrast mask causes substantial binocular threshold elevation for a transient vertical target, and this declines from a mask orientation of 0° to about 40° (indicating tuning), and then more gently to 90°, where it remains at a factor of ∼4. We also confirm that cross-orientation masking is diminished or abolished at high spatial frequencies and for sustained temporal modulation. We fitted a simple model of pedestal masking and cross-orientation suppression (XOS) to our data and those of G. C. Phillips and H. R. Wilson (1984) and found the dependency of orientation bandwidth on spatial frequency to be much less than previously supposed. An extension of our linear spatial pooling model of contrast gain control and dilution masking (T. S. Meese & R. J. Summers, 2007) is also shown to be consistent with our results using filter bandwidths of ±20°. Both models include tightly and broadly tuned components of divisive suppression. More generally, because XOS and/or dilution masking can affect the shape of orientation-masking curves, we caution that variations in bandwidth estimates might reflect variations in processes that have nothing to do with filter bandwidth.

Large-scale functional networks connect differently for processing words and symbol strings.

PubMed

Liljeström, Mia; Vartiainen, Johanna; Kujala, Jan; Salmelin, Riitta

2018-01-01

Reconfigurations of synchronized large-scale networks are thought to be central neural mechanisms that support cognition and behavior in the human brain. Magnetoencephalography (MEG) recordings together with recent advances in network analysis now allow for sub-second snapshots of such networks. In the present study, we compared frequency-resolved functional connectivity patterns underlying reading of single words and visual recognition of symbol strings. Word reading emphasized coherence in a left-lateralized network with nodes in classical perisylvian language regions, whereas symbol processing recruited a bilateral network, including connections between frontal and parietal regions previously associated with spatial attention and visual working memory. Our results illustrate the flexible nature of functional networks, whereby processing of different form categories, written words vs. symbol strings, leads to the formation of large-scale functional networks that operate at distinct oscillatory frequencies and incorporate task-relevant regions. These results suggest that category-specific processing should be viewed not so much as a local process but as a distributed neural process implemented in signature networks. For words, increased coherence was detected particularly in the alpha (8-13 Hz) and high gamma (60-90 Hz) frequency bands, whereas increased coherence for symbol strings was observed in the high beta (21-29 Hz) and low gamma (30-45 Hz) frequency range. These findings attest to the role of coherence in specific frequency bands as a general mechanism for integrating stimulus-dependent information across brain regions.

Spatial layout of letters in nonwords affects visual short-term memory load: evidence from human electrophysiology.

PubMed

Prime, David; Dell'acqua, Roberto; Arguin, Martin; Gosselin, Frédéric; Jolicœur, Pierre

2011-03-01

The sustained posterior contralateral negativity (SPCN) was used to investigate the effect of spatial layout on the maintenance of letters in VSTM. SPCN amplitude was measured for words, nonwords, and scrambled nonwords. We reexamined the effects of spatial layout of letters on SPCN amplitude in a design that equated the mean frequency of use of each position. Scrambled letters that did not form words elicited a larger SPCN than either words or nonwords, indicating lower VSTM load for nonwords presented in a typical horizontal array than the load observed for the same letters presented in spatially scrambled locations. In contrast, prior research has shown that the spatial extent of arrays of simple stimuli did not influence the amplitude of the SPCN. Thus, the present results indicate the existence of encoding and VSTM maintenance mechanisms specific to letter and word processing. Copyright © 2010 Society for Psychophysiological Research.

Vision based tunnel inspection using non-rigid registration

NASA Astrophysics Data System (ADS)

Badshah, Amir; Ullah, Shan; Shahzad, Danish

2015-04-01

Growing numbers of long tunnels across the globe has increased the need for safety measurements and inspections of tunnels in these days. To avoid serious damages, tunnel inspection is highly recommended at regular intervals of time to find any deformations or cracks at the right time. While following the stringent safety and tunnel accessibility standards, conventional geodetic surveying using techniques of civil engineering and other manual and mechanical methods are time consuming and results in troublesome of routine life. An automatic tunnel inspection by image processing techniques using non rigid registration has been proposed. There are many other image processing methods used for image registration purposes. Most of the processes are operation of images in its spatial domain like finding edges and corners by Harris edge detection method. These methods are quite time consuming and fail for some or other reasons like for blurred or images with noise. Due to use of image features directly by these methods in the process, are known by the group, correlation by image features. The other method is featureless correlation, in which the images are converted into its frequency domain and then correlated with each other. The shift in spatial domain is the same as in frequency domain, but the processing is order faster than in spatial domain. In the proposed method modified normalized phase correlation has been used to find any shift between two images. As pre pre-processing the tunnel images i.e. reference and template are divided into small patches. All these relative patches are registered by the proposed modified normalized phase correlation. By the application of the proposed algorithm we get the pixel movement of the images. And then these pixels shifts are converted to measuring units like mm, cm etc. After the complete process if there is any shift in the tunnel at described points are located.

Critical band masking reveals the effects of optical distortions on the channel mediating letter identification.

PubMed

Young, Laura K; Smithson, Hannah E

2014-01-01

There is evidence that letter identification is mediated by only a narrow band of spatial frequencies and that the center frequency of the neural channel thought to underlie this selectivity is related to the size of the letters. When letters are spatially filtered (at a fixed size) the channel tuning characteristics change according to the properties of the spatial filter (Majaj et al., 2002). Optical aberrations in the eye act to spatially filter the image formed on the retina-their effect is generally to attenuate high frequencies more than low frequencies but often in a non-monotonic way. We might expect the change in the spatial frequency spectrum caused by the aberration to predict the shift in channel tuning observed for aberrated letters. We show that this is not the case. We used critical-band masking to estimate channel-tuning in the presence of three types of aberration-defocus, coma and secondary astigmatism. We found that the maximum masking was shifted to lower frequencies in the presence of an aberration and that this result was not simply predicted by the spatial-frequency-dependent degradation in image quality, assessed via metrics that have previously been shown to correlate well with performance loss in the presence of an aberration. We show that if image quality effects are taken into account (using visual Strehl metrics), the neural channel required to model the data is shifted to lower frequencies compared to the control (no-aberration) condition. Additionally, we show that when spurious resolution (caused by π phase shifts in the optical transfer function) in the image is masked, the channel tuning properties for aberrated letters are affected, suggesting that there may be interference between visual channels. Even in the presence of simulated aberrations, whose properties change from trial-to-trial, observers exhibit flexibility in selecting the spatial frequencies that support letter identification.

SSD with generalized phase modulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rothenberg, J.

1996-01-09

Smoothing by spectral dispersion (SSD) with standard frequency modulation (FM), although simple to implement, has the disadvantage that low spatial frequencies present in the spectrum of the target illumination are not smoothed as effectively as with a more general smoothing method (eg, induced spatial incoherence method). The reduced smoothing performance of standard FM-SSD can result in spectral power of the speckle noise at these low spatial frequencies as much as one order of magnitude larger than that achieved with a more general method. In fact, at small integration times FM-SSD has no smoothing effect at all for a broad bandmore » of low spatial frequencies. This effect may have important implications for both direct and indirect drive ICF.« less

Image processing analysis of traditional Gestalt vision experiments

NASA Astrophysics Data System (ADS)

McCann, John J.

2002-06-01

In the late 19th century, the Gestalt Psychology rebelled against the popular new science of Psychophysics. The Gestalt revolution used many fascinating visual examples to illustrate that the whole is greater than the sum of all the parts. Color constancy was an important example. The physical interpretation of sensations and their quantification by JNDs and Weber fractions were met with innumerable examples in which two 'identical' physical stimuli did not look the same. The fact that large changes in the color of the illumination failed to change color appearance in real scenes demanded something more than quantifying the psychophysical response of a single pixel. The debates continues today with proponents of both physical, pixel-based colorimetry and perceptual, image- based cognitive interpretations. Modern instrumentation has made colorimetric pixel measurement universal. As well, new examples of unconscious inference continue to be reported in the literature. Image processing provides a new way of analyzing familiar Gestalt displays. Since the pioneering experiments by Fergus Campbell and Land, we know that human vision has independent spatial channels and independent color channels. Color matching data from color constancy experiments agrees with spatial comparison analysis. In this analysis, simple spatial processes can explain the different appearances of 'identical' stimuli by analyzing the multiresolution spatial properties of their surrounds. Benary's Cross, White's Effect, the Checkerboard Illusion and the Dungeon Illusion can all be understood by the analysis of their low-spatial-frequency components. Just as with color constancy, these Gestalt images are most simply described by the analysis of spatial components. Simple spatial mechanisms account for the appearance of 'identical' stimuli in complex scenes. It does not require complex, cognitive processes to calculate appearances in familiar Gestalt experiments.

Imaging of the interaction of low frequency electric fields with biological tissues by optical coherence tomography

NASA Astrophysics Data System (ADS)

Peña, Adrian F.; Devine, Jack; Doronin, Alexander; Meglinski, Igor

2014-03-01

We report the use of conventional Optical Coherence Tomography (OCT) for visualization of propagation of low frequency electric field in soft biological tissues ex vivo. To increase the overall quality of the experimental images an adaptive Wiener filtering technique has been employed. Fourier domain correlation has been subsequently applied to enhance spatial resolution of images of biological tissues influenced by low frequency electric field. Image processing has been performed on Graphics Processing Units (GPUs) utilizing Compute Unified Device Architecture (CUDA) framework in the frequencydomain. The results show that variation in voltage and frequency of the applied electric field relates exponentially to the magnitude of its influence on biological tissue. The magnitude of influence is about twice more for fresh tissue samples in comparison to non-fresh ones. The obtained results suggest that OCT can be used for observation and quantitative evaluation of the electro-kinetic changes in biological tissues under different physiological conditions, functional electrical stimulation, and potentially can be used non-invasively for food quality control.

Cross-media color reproduction using the frequency-based spatial gamut mapping algorithm based on human color vision

NASA Astrophysics Data System (ADS)

Wu, Guangyuan; Niu, Shijun; Li, Xiaozhou; Hu, Guichun

2018-04-01

Due to the increasing globalization of printing industry, remoting proofing will become the inevitable development trend. Cross-media color reproduction will occur in different color gamuts using remote proofing technologies, which usually leads to the problem of incompatible color gamut. In this paper, to achieve equivalent color reproduction between a monitor and a printer, a frequency-based spatial gamut mapping algorithm is proposed for decreasing the loss of visual color information. The design of algorithm is based on the contrast sensitivity functions (CSF), which exploited CSF spatial filter to preserve luminance of the high spatial frequencies and chrominance of the low frequencies. First we show a general framework for how to apply CSF spatial filter in retention of relevant visual information. Then we compare the proposed framework with HPMINDE, CUSP, Bala's algorithm. The psychophysical experimental results indicated the good performance of the proposed algorithm.

An underestimated role of precipitation frequency in regulating summer soil moisture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Chaoyang; Chen, Jing M.; Pumpanen, Jukka

2012-04-26

Soil moisture induced droughts are expected to become more frequent under future global climate change. Precipitation has been previously assumed to be mainly responsible for variability in summer soil moisture. However, little is known about the impacts of precipitation frequency on summer soil moisture, either interannually or spatially. To better understand the temporal and spatial drivers of summer drought, 415 site yr measurements observed at 75 flux sites world wide were used to analyze the temporal and spatial relationships between summer soil water content (SWC) and the precipitation frequencies at various temporal scales, i.e., from half-hourly, 3, 6, 12 andmore » 24 h measurements. Summer precipitation was found to be an indicator of interannual SWC variability with r of 0.49 (p < 0.001) for the overall dataset. However, interannual variability in summer SWC was also significantly correlated with the five precipitation frequencies and the sub-daily precipitation frequencies seemed to explain the interannual SWC variability better than the total of precipitation. Spatially, all these precipitation frequencies were better indicators of summer SWC than precipitation totals, but these better performances were only observed in non-forest ecosystems. Our results demonstrate that precipitation frequency may play an important role in regulating both interannual and spatial variations of summer SWC, which has probably been overlooked or underestimated. However, the spatial interpretation should carefully consider other factors, such as the plant functional types and soil characteristics of diverse ecoregions.« less

Neural processing of high and low spatial frequency information in faces changes across development: qualitative changes in face processing during adolescence.

PubMed

Peters, Judith C; Vlamings, Petra; Kemner, Chantal

2013-05-01

Face perception in adults depends on skilled processing of interattribute distances ('configural' processing), which is disrupted for faces presented in inverted orientation (face inversion effect or FIE). Children are not proficient in configural processing, and this might relate to an underlying immaturity to use facial information in low spatial frequency (SF) ranges, which capture the coarse information needed for configural processing. We hypothesized that during adolescence a shift from use of high to low SF information takes place. Therefore, we studied the influence of SF content on neural face processing in groups of children (9-10 years), adolescents (14-15 years) and young adults (21-29 years) by measuring event-related potentials (ERPs) to upright and inverted faces which varied in SF content. Results revealed that children show a neural FIE in early processing stages (i.e. P1; generated in early visual areas), suggesting a superficial, global facial analysis. In contrast, ERPs of adults revealed an FIE at later processing stages (i.e. N170; generated in face-selective, higher visual areas). Interestingly, adolescents showed FIEs in both processing stages, suggesting a hybrid developmental stage. Furthermore, adolescents and adults showed FIEs for stimuli containing low SF information, whereas such effects were driven by both low and high SF information in children. These results indicate that face processing has a protracted maturational course into adolescence, and is dependent on changes in SF processing. During adolescence, sensitivity to configural cues is developed, which aids the fast and holistic processing that is so special for faces. © 2013 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Spatial orientation of different frequencies within the echolocation beam of a Tursiops truncatus and Pseudorca crassidens.

PubMed

Ibsen, Stuart D; Nachtigall, Paul E; Krause-Nehring, Jacqueline; Kloepper, Laura; Breese, Marlee; Li, Songhai; Vlachos, Stephanie

2012-08-01

A two-dimensional array of 16 hydrophones was created to map the spatial distribution of different frequencies within the echolocation beam of a Tursiops truncatus and a Pseudorca crassidens. It was previously shown that both the Tursiops and Pseudorca only paid attention to frequencies between 29 and 42 kHz while echolocating. Both individuals tightly focused the 30 kHz frequency and the spatial location of the focus was consistently pointed toward the target. At 50 kHz the beam was less focused and less precisely pointed at the target. At 100 kHz the focus was often completely lost and was not pointed at the target. This indicates that these individuals actively focused the beam toward the target only in the frequency range they paid attention to. Frequencies outside this range were left unfocused and undirected. This focusing was probably achieved through sensorimotor control of the melon morphology and nasal air sacs. This indicates that both morphologically different species can control the spatial distribution of different frequency ranges within the echolocation beam to create consistent ensonation of desired targets.

Soil moisture observations using L-, C-, and X-band microwave radiometers

NASA Astrophysics Data System (ADS)

Bolten, John Dennis

The purpose of this thesis is to further the current understanding of soil moisture remote sensing under varying conditions using L-, C-, and X-band. Aircraft and satellite instruments are used to investigate the effects of frequency and spatial resolution on soil moisture sensitivity. The specific objectives of the research are to examine multi-scale observed and modeled microwave radiobrightness, evaluate new EOS Aqua Advanced Microwave Scanning Radiometer (AMSR-E) brightness temperature and soil moisture retrievals, and examine future satellite-based technologies for soil moisture sensing. The cycling of Earth's water, energy and carbon is vital to understanding global climate. Over land, these processes are largely dependent on the amount of moisture within the top few centimeters of the soil. However, there are currently no methods available that can accurately characterize Earth's soil moisture layer at the spatial scales or temporal resolutions appropriate for climate modeling. The current work uses ground truth, satellite and aircraft remote sensing data from three large-scale field experiments having different land surface, topographic and climate conditions. A physically-based radiative transfer model is used to simulate the observed aircraft and satellite measurements using spatially and temporally co-located surface parameters. A robust analysis of surface heterogeneity and scaling is possible due to the combination of multiple datasets from a range of microwave frequencies and field conditions. Accurate characterization of spatial and temporal variability of soil moisture during the three field experiments is achieved through sensor calibration and algorithm validation. Comparisons of satellite observations and resampled aircraft observations are made using soil moisture from a Numerical Weather Prediction (NWP) model in order to further demonstrate a soil moisture correlation where point data was unavailable. The influence of vegetation, spatial scaling, and surface heterogeneity on multi-scale soil moisture prediction is presented. This work demonstrates that derived soil moisture using remote sensing provides a better coverage of soil moisture spatial variability than traditional in-situ sensors. Effects of spatial scale were shown to be less significant than frequency on soil moisture sensitivity. Retrievals of soil moisture using the current methods proved inadequate under some conditions; however, this study demonstrates the need for concurrent spaceborne frequencies including L-, C, and X-band.

Primitive Auditory Memory Is Correlated with Spatial Unmasking That Is Based on Direct-Reflection Integration

PubMed Central

Li, Huahui; Kong, Lingzhi; Wu, Xihong; Li, Liang

2013-01-01

In reverberant rooms with multiple-people talking, spatial separation between speech sources improves recognition of attended speech, even though both the head-shadowing and interaural-interaction unmasking cues are limited by numerous reflections. It is the perceptual integration between the direct wave and its reflections that bridges the direct-reflection temporal gaps and results in the spatial unmasking under reverberant conditions. This study further investigated (1) the temporal dynamic of the direct-reflection-integration-based spatial unmasking as a function of the reflection delay, and (2) whether this temporal dynamic is correlated with the listeners’ auditory ability to temporally retain raw acoustic signals (i.e., the fast decaying primitive auditory memory, PAM). The results showed that recognition of the target speech against the speech-masker background is a descending exponential function of the delay of the simulated target reflection. In addition, the temporal extent of PAM is frequency dependent and markedly longer than that for perceptual fusion. More importantly, the temporal dynamic of the speech-recognition function is significantly correlated with the temporal extent of the PAM of low-frequency raw signals. Thus, we propose that a chain process, which links the earlier-stage PAM with the later-stage correlation computation, perceptual integration, and attention facilitation, plays a role in spatially unmasking target speech under reverberant conditions. PMID:23658664

Rockfall hazard analysis using LiDAR and spatial modeling

NASA Astrophysics Data System (ADS)

Lan, Hengxing; Martin, C. Derek; Zhou, Chenghu; Lim, Chang Ho

2010-05-01

Rockfalls have been significant geohazards along the Canadian Class 1 Railways (CN Rail and CP Rail) since their construction in the late 1800s. These rockfalls cause damage to infrastructure, interruption of business, and environmental impacts, and their occurrence varies both spatially and temporally. The proactive management of these rockfall hazards requires enabling technologies. This paper discusses a hazard assessment strategy for rockfalls along a section of a Canadian railway using LiDAR and spatial modeling. LiDAR provides accurate topographical information of the source area of rockfalls and along their paths. Spatial modeling was conducted using Rockfall Analyst, a three dimensional extension to GIS, to determine the characteristics of the rockfalls in terms of travel distance, velocity and energy. Historical rockfall records were used to calibrate the physical characteristics of the rockfall processes. The results based on a high-resolution digital elevation model from a LiDAR dataset were compared with those based on a coarse digital elevation model. A comprehensive methodology for rockfall hazard assessment is proposed which takes into account the characteristics of source areas, the physical processes of rockfalls and the spatial attribution of their frequency and energy.

Stellar interferometers and hypertelescopes: new insights on an angular spatial frequency approach to their non-invariant imaging

NASA Astrophysics Data System (ADS)

Dettwiller, L.; Lépine, T.

2017-12-01

A general and pure wave theory of image formation for all types of stellar interferometers, including hypertelescopes, is developed in the frame of Fresnel's paraxial approximations of diffraction. For a hypertelescope, we show that the severe lack of translation invariance leads to multiple and strong spatial frequency heterodyning, which codes the very high frequencies detected by the hypertelescope into medium spatial frequencies and introduces a moiré-type ambiguity for extended objects. This explains mathematically the disappointing appearance of poor resolution observed in some image simulations for hypertelescopes.

Spatial contrast sensitivity - Effects of age, test-retest, and psychophysical method

NASA Technical Reports Server (NTRS)

Higgins, Kent E.; Jaffe, Myles J.; Caruso, Rafael C.; Demonasterio, Francisco M.

1988-01-01

Two different psychophysical methods were used to test the spatial contrast sensitivity in normal subjects from five age groups. The method of adjustment showed a decline in sensitivity with increasing age at all spatial frequencies, while the forced-choice procedure showed an age-related decline predominantly at high spatial frequencies. It is suggested that a neural component is responsible for this decline.

Surface Currents and Winds at the Delaware Bay Mouth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muscarella, P A; Barton, N P; Lipphardt, B L

2011-04-06

Knowledge of the circulation of estuaries and adjacent shelf waters has relied on hydrographic measurements, moorings, and local wind observations usually removed from the region of interest. Although these observations are certainly sufficient to identify major characteristics, they lack both spatial resolution and temporal coverage. High resolution synoptic observations are required to identify important coastal processes at smaller scales. Long observation periods are needed to properly sample low-frequency processes that may also be important. The introduction of high-frequency (HF) radar measurements and regional wind models for coastal studies is changing this situation. Here we analyze synoptic, high-resolution surface winds andmore » currents in the Delaware Bay mouth over an eight-month period (October 2007 through May 2008). The surface currents were measured by two high-frequency radars while the surface winds were extracted from a data-assimilating regional wind model. To illustrate the utility of these monitoring tools we focus on two 45-day periods which previously were shown to present contrasting pictures of the circulation. One, the low-outflow period is from 1 October through 14 November 2007; the other is the high-outflow period from 3 March through 16 April 2008. The large-scale characteristics noted by previous workers are clearly corroborated. Specifically the M2 tide dominates the surface currents, and the Delaware Bay outflow plume is clearly evident in the low frequency currents. Several new aspects of the surface circulation were also identified. These include a map of the spatial variability of the M2 tide (validating an earlier model study), persistent low-frequency cross-mouth flow, and a rapid response of the surface currents to a changing wind field. However, strong wind episodes did not persist long enough to set up a sustained Ekman response.« less

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging.

PubMed

Nadeau, Kyle P; Rice, Tyler B; Durkin, Anthony J; Tromberg, Bruce J

2015-11-01

We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging

PubMed Central

Nadeau, Kyle P.; Rice, Tyler B.; Durkin, Anthony J.; Tromberg, Bruce J.

2015-01-01

Abstract. We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI. PMID:26524682

Stochastic simulation of spatially correlated geo-processes

USGS Publications Warehouse

Christakos, G.

1987-01-01

In this study, developments in the theory of stochastic simulation are discussed. The unifying element is the notion of Radon projection in Euclidean spaces. This notion provides a natural way of reconstructing the real process from a corresponding process observable on a reduced dimensionality space, where analysis is theoretically easier and computationally tractable. Within this framework, the concept of space transformation is defined and several of its properties, which are of significant importance within the context of spatially correlated processes, are explored. The turning bands operator is shown to follow from this. This strengthens considerably the theoretical background of the geostatistical method of simulation, and some new results are obtained in both the space and frequency domains. The inverse problem is solved generally and the applicability of the method is extended to anisotropic as well as integrated processes. Some ill-posed problems of the inverse operator are discussed. Effects of the measurement error and impulses at origin are examined. Important features of the simulated process as described by geomechanical laws, the morphology of the deposit, etc., may be incorporated in the analysis. The simulation may become a model-dependent procedure and this, in turn, may provide numerical solutions to spatial-temporal geologic models. Because the spatial simu??lation may be technically reduced to unidimensional simulations, various techniques of generating one-dimensional realizations are reviewed. To link theory and practice, an example is computed in detail. ?? 1987 International Association for Mathematical Geology.

Slow-theta power decreases during item-place encoding predict spatial accuracy of subsequent context recall.

PubMed

Crespo-García, Maité; Zeiller, Monika; Leupold, Claudia; Kreiselmeyer, Gernot; Rampp, Stefan; Hamer, Hajo M; Dalal, Sarang S

2016-11-15

Human hippocampal theta oscillations play a key role in accurate spatial coding. Associative encoding involves similar hippocampal networks but, paradoxically, is also characterized by theta power decreases. Here, we investigated how theta activity relates to associative encoding of place contexts resulting in accurate navigation. Using MEG, we found that slow-theta (2-5Hz) power negatively correlated with subsequent spatial accuracy for virtual contextual locations in posterior hippocampus and other cortical structures involved in spatial cognition. A rare opportunity to simultaneously record MEG and intracranial EEG in an epilepsy patient provided crucial insights: during power decreases, slow-theta in right anterior hippocampus and left inferior frontal gyrus phase-led the left temporal cortex and predicted spatial accuracy. Our findings indicate that decreased slow-theta activity reflects local and long-range neural mechanisms that encode accurate spatial contexts, and strengthens the view that local suppression of low-frequency activity is essential for more efficient processing of detailed information. Copyright © 2016 Elsevier Inc. All rights reserved.

Precise and fast spatial-frequency analysis using the iterative local Fourier transform.

PubMed

Lee, Sukmock; Choi, Heejoo; Kim, Dae Wook

2016-09-19

The use of the discrete Fourier transform has decreased since the introduction of the fast Fourier transform (fFT), which is a numerically efficient computing process. This paper presents the iterative local Fourier transform (ilFT), a set of new processing algorithms that iteratively apply the discrete Fourier transform within a local and optimal frequency domain. The new technique achieves 2¹⁰ times higher frequency resolution than the fFT within a comparable computation time. The method's superb computing efficiency, high resolution, spectrum zoom-in capability, and overall performance are evaluated and compared to other advanced high-resolution Fourier transform techniques, such as the fFT combined with several fitting methods. The effectiveness of the ilFT is demonstrated through the data analysis of a set of Talbot self-images (1280 × 1024 pixels) obtained with an experimental setup using grating in a diverging beam produced by a coherent point source.

Non-contact defect diagnostics in Cz-Si wafers using resonance ultrasonic vibrations

NASA Astrophysics Data System (ADS)

Belyaev, A.; Kochelap, V. A.; Tarasov, I.; Ostapenko, S.

2001-01-01

A new resonance effect of generation of sub-harmonic acoustic vibrations was applied to characterize defects in as-grown and processed Cz-Si wafers. Ultrasonic vibrations were generated into standard 8″ wafers using an external ultrasonic transducer and their amplitude recorded in a non-contact mode using a scanning acoustic probe. By tuning the frequency, f, of the transducer we observed generation of intense sub-harmonic acoustic mode ("whistle" or w-mode) with f/2 frequency. The characteristics of the w-mode-amplitude dependence, frequency scans, spatial distribution allow a clear distinction versus harmonic vibrations of the same wafer. The origin of sub-harmonic vibrations observed on 8″ Cz-Si wafers is attributed to a parametric resonance of flexural vibrations in thin silicon circular plates. We present evidence that "whistle" effect shows a strong dependence on the wafer's growth and processing history and can be used for quality assurance purposes.

Observation of sum-frequency-generation-induced cascaded four-wave mixing using two crossing femtosecond laser pulses in a 0.1 mm beta-barium-borate crystal.

PubMed

Liu, Weimin; Zhu, Liangdong; Fang, Chong

2012-09-15

We demonstrate the simultaneous generation of multicolor femtosecond laser pulses spanning the wavelength range from UV to near IR in a 0.1 mm Type I beta-barium borate crystal from 800 nm fundamental and weak IR super-continuum white light (SCWL) pulses. The multicolor broadband laser pulses observed are attributed to two concomitant cascaded four-wave mixing (CFWM) processes as corroborated by calculation: (1) directly from the two incident laser pulses; (2) by the sum-frequency generation (SFG) induced CFWM process (SFGFWM). The latter signal arises from the interaction between the frequency-doubled fundamental pulse (400 nm) and the SFG pulse generated in between the fundamental and IR-SCWL pulses. The versatility and simplicity of this spatially dispersed multicolor self-compressed laser pulse generation offer compact and attractive methods to conduct femtosecond stimulated Raman spectroscopy and time-resolved multicolor spectroscopy.

Masking potency and whiteness of noise at various noise check sizes.

PubMed

Kukkonen, H; Rovamo, J; Näsänen, R

1995-02-01

The masking effect of spatial noise can be increased by increasing either the rms contrast or check size of noise. In this study, the authors investigated the largest noise check size that still mimics the effect of white noise in grating detection and how it depends on the bandwidth and spatial frequency of a grating. The authors measured contrast energy thresholds, E, for vertical cosine gratings at various spatial frequencies and bandwidths. Gratings were embedded in two-dimensional spatial noise. The side length of the square noise checks was varied in the experiments. The spectral density, N(0,0), of white spatial noise at zero frequency was calculated by multiplying the noise check area by the rms contrast of noise squared. The physical signal-to-noise ratio at threshold [E/N(0,0)]0.5 was initially constant but then started to decrease. The largest noise check that still produced a constant physical signal-to-noise ratio at threshold was directly proportional to the spatial frequency. When expressed as a fraction of grating cycle, the largest noise check size depended only on stimulus bandwidth. The smallest number of noise checks per grating cycle needed to mimic the effect of white noise decreased from 4.2 to 2.6 when the number of grating cycles increased from 1 to 64. Spatial noise can be regarded as white in grating detection if there are at least four square noise checks per grating cycle at all spatial frequencies.

A three-dimensional point process model for the spatial distribution of disease occurrence in relation to an exposure source.

PubMed

Grell, Kathrine; Diggle, Peter J; Frederiksen, Kirsten; Schüz, Joachim; Cardis, Elisabeth; Andersen, Per K

2015-10-15

We study methods for how to include the spatial distribution of tumours when investigating the relation between brain tumours and the exposure from radio frequency electromagnetic fields caused by mobile phone use. Our suggested point process model is adapted from studies investigating spatial aggregation of a disease around a source of potential hazard in environmental epidemiology, where now the source is the preferred ear of each phone user. In this context, the spatial distribution is a distribution over a sample of patients rather than over multiple disease cases within one geographical area. We show how the distance relation between tumour and phone can be modelled nonparametrically and, with various parametric functions, how covariates can be included in the model and how to test for the effect of distance. To illustrate the models, we apply them to a subset of the data from the Interphone Study, a large multinational case-control study on the association between brain tumours and mobile phone use. Copyright © 2015 John Wiley & Sons, Ltd.

Temporal resolution of orientation-defined texture segregation: a VEP study.

PubMed

Lachapelle, Julie; McKerral, Michelle; Jauffret, Colin; Bach, Michael

2008-09-01

Orientation is one of the visual dimensions that subserve figure-ground discrimination. A spatial gradient in orientation leads to "texture segregation", which is thought to be concurrent parallel processing across the visual field, without scanning. In the visual-evoked potential (VEP) a component can be isolated which is related to texture segregation ("tsVEP"). Our objective was to evaluate the temporal frequency dependence of the tsVEP to compare processing speed of low-level features (e.g., orientation, using the VEP, here denoted llVEP) with texture segregation because of a recent literature controversy in that regard. Visual-evoked potentials (VEPs) were recorded in seven normal adults. Oriented line segments of 0.1 degrees x 0.8 degrees at 100% contrast were presented in four different arrangements: either oriented in parallel for two homogeneous stimuli (from which were obtained the low-level VEP (llVEP)) or with a 90 degrees orientation gradient for two textured ones (from which were obtained the texture VEP). The orientation texture condition was presented at eight different temporal frequencies ranging from 7.5 to 45 Hz. Fourier analysis was used to isolate low-level components at the pattern-change frequency and texture-segregation components at half that frequency. For all subjects, there was lower high-cutoff frequency for tsVEP than for llVEPs, on average 12 Hz vs. 17 Hz (P = 0.017). The results suggest that the processing of feature gradients to extract texture segregation requires additional processing time, resulting in a lower fusion frequency.

Spatial-temporal variability of soil water content in a cropland-shelterbelt-desert site in an arid inland river basin of Northwest China

NASA Astrophysics Data System (ADS)

Shen, Qin; Gao, Guangyao; Hu, Wei; Fu, Bojie

2016-09-01

Knowledge of the spatial-temporal variability of soil water content (SWC) is critical for understanding a range of hydrological processes. In this study, the spatial variance and temporal stability of SWC were investigated in a cropland-shelterbelt-desert site at the oasis-desert ecotone in the middle of the Heihe River Basin, China. The SWC was measured on 65 occasions to a depth of 2.8 m at 45 locations during two growing seasons from 2012 to 2013. The standard deviation of the SWC versus the mean SWC exhibited a convex upward relationship in the shelterbelt with the greatest spatial variation at the SWC of around 22.0%, whereas a linearly increasing relationship was observed for the cropland, desert, and land use pattern. The standard deviation of the relative difference was positively linearly correlated with the SWC (p < 0.05) for the land use pattern, whereas such a relationship was not found in the three land use types. The spatial pattern of the SWC was more time stable for the land use pattern, followed by desert, shelterbelt, and cropland. The spatial pattern of SWC changed dramatically among different soil layers. The locations representing the mean SWC varied with the depth, and no location could represent the whole soil profile due to different soil texture, root distribution and irrigation management. The representative locations of each soil layer could be used to estimate the mean SWC well. The statistics of temporal stability of the SWC could be presented equally well with a low frequency of observation (30-day interval) as with a high frequency (5-day interval). Sampling frequency had little effect on the selection of the representative locations of the field mean SWC. This study provides useful information for designing the optimal strategy for sampling SWC at the oasis-desert ecotone in the arid inland river basin.

Visual sensitivity to spatially sampled modulation in human observers

NASA Technical Reports Server (NTRS)

Mulligan, Jeffrey B.; Macleod, Donald I. A.

1991-01-01

Thresholds were measured for detecting spatial luminance modulation in regular lattices of visually discrete dots. Thresholds for modulation of a lattice are generally higher than the corresponding threshold for modulation of a continuous field, and the size of the threshold elevation, which depends on the spacing of the lattice elements, can be as large as a one log unit. The largest threshold elevations are seen when the sample spacing is 12 min arc or greater. Theories based on response compression cannot explain the further observation that the threshold elevations due to spatial sampling are also dependent on modulation frequency: the greatest elevations occur with higher modulation frequencies. The idea that this is due to masking of the modulation frequency by the spatial frequencies in the sampling lattice is considered.

Image enhancement filters significantly improve reading performance for low vision observers

NASA Technical Reports Server (NTRS)

Lawton, T. B.

1992-01-01

As people age, so do their photoreceptors; many photoreceptors in central vision stop functioning when a person reaches their late sixties or early seventies. Low vision observers with losses in central vision, those with age-related maculopathies, were studied. Low vision observers no longer see high spatial frequencies, being unable to resolve fine edge detail. We developed image enhancement filters to compensate for the low vision observer's losses in contrast sensitivity to intermediate and high spatial frequencies. The filters work by boosting the amplitude of the less visible intermediate spatial frequencies. The lower spatial frequencies. These image enhancement filters not only reduce the magnification needed for reading by up to 70 percent, but they also increase the observer's reading speed by 2-4 times. A summary of this research is presented.

Wave excitations of drifting two-dimensional electron gas under strong inelastic scattering

NASA Astrophysics Data System (ADS)

Korotyeyev, V. V.; Kochelap, V. A.; Varani, L.

2012-10-01

We have analyzed low-temperature behavior of two-dimensional electron gas in polar heterostructures subjected to a high electric field. When the optical phonon emission is the fastest relaxation process, we have found existence of collective wave-like excitations of the electrons. These wave-like excitations are periodic in time oscillations of the electrons in both real and momentum spaces. The excitation spectra are of multi-branch character with considerable spatial dispersion. There are one acoustic-type and a number of optical-type branches of the spectra. Their small damping is caused by quasi-elastic scattering of the electrons and formation of relevant space charge. Also there exist waves with zero frequency and finite spatial periods—the standing waves. The found excitations of the electron gas can be interpreted as synchronous in time and real space manifestation of well-known optical-phonon-transient-time-resonance. Estimates of parameters of the excitations for two polar heterostructures, GaN/AlGaN and ZnO/MgZnO, have shown that excitation frequencies are in THz-frequency range, while standing wave periods are in sub-micrometer region.

Spatial acoustic signal processing for immersive communication

NASA Astrophysics Data System (ADS)

Atkins, Joshua

Computing is rapidly becoming ubiquitous as users expect devices that can augment and interact naturally with the world around them. In these systems it is necessary to have an acoustic front-end that is able to capture and reproduce natural human communication. Whether the end point is a speech recognizer or another human listener, the reduction of noise, reverberation, and acoustic echoes are all necessary and complex challenges. The focus of this dissertation is to provide a general method for approaching these problems using spherical microphone and loudspeaker arrays.. In this work, a theory of capturing and reproducing three-dimensional acoustic fields is introduced from a signal processing perspective. In particular, the decomposition of the spatial part of the acoustic field into an orthogonal basis of spherical harmonics provides not only a general framework for analysis, but also many processing advantages. The spatial sampling error limits the upper frequency range with which a sound field can be accurately captured or reproduced. In broadband arrays, the cost and complexity of using multiple transducers is an issue. This work provides a flexible optimization method for determining the location of array elements to minimize the spatial aliasing error. The low frequency array processing ability is also limited by the SNR, mismatch, and placement error of transducers. To address this, a robust processing method is introduced and used to design a reproduction system for rendering over arbitrary loudspeaker arrays or binaurally over headphones. In addition to the beamforming problem, the multichannel acoustic echo cancellation (MCAEC) issue is also addressed. A MCAEC must adaptively estimate and track the constantly changing loudspeaker-room-microphone response to remove the sound field presented over the loudspeakers from that captured by the microphones. In the multichannel case, the system is overdetermined and many adaptive schemes fail to converge to the true impulse response. This forces the need to track both the near and far end room responses. A transform domain method that mitigates this problem is derived and implemented. Results with a real system using a 16-channel loudspeaker array and 32-channel microphone array are presented.

Patterns in Temporal Variability of Temperature, Oxygen and pH along an Environmental Gradient in a Coral Reef

PubMed Central

Guadayol, Òscar; Silbiger, Nyssa J.; Donahue, Megan J.; Thomas, Florence I. M.

2014-01-01

Spatial and temporal environmental variability are important drivers of ecological processes at all scales. As new tools allow the in situ exploration of individual responses to fluctuations, ecologically meaningful ways of characterizing environmental variability at organism scales are needed. We investigated the fine-scale spatial heterogeneity of high-frequency temporal variability in temperature, dissolved oxygen concentration, and pH experienced by benthic organisms in a shallow coastal coral reef. We used a spatio-temporal sampling design, consisting of 21 short-term time-series located along a reef flat-to-reef slope transect, coupled to a long-term station monitoring water column changes. Spectral analyses revealed sharp gradients in variance decomposed by frequency, as well as differences between physically-driven and biologically-reactive parameters. These results highlight the importance of environmental variance at organismal scales and present a new sampling scheme for exploring this variability in situ. PMID:24416364

Spatial-frequency Fourier polarimetry of the complex degree of mutual anisotropy of linear and circular birefringence in the diagnostics of oncological changes in morphological structure of biological tissues

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ushenko, Yu A; Gorskii, M P; Dubolazov, A V

2012-08-31

Theory of polarisation-correlation analysis of laser images of histological sections of biopsy material from cervix tissue based on spatial frequency selection of linear and circular birefringence mechanisms is formulated. Comparative results of measuring the coordinate distributions of the complex degree of mutual anisotropy (CDMA), produced by fibrillar networks formed by myosin and collagen fibres of cervix tissue in different pathological conditions, namely, pre-cancer (dysplasia) and cancer (adenocarcinoma), are presented. The values and variation ranges of statistical (moments of the first - fourth order), correlation (excess-autocorrelation functions), and fractal (slopes of approximating curves and dispersion of extrema of logarithmic dependences ofmore » power spectra) parameters of the CDMA coordinate distributions are studied. Objective criteria for pathology diagnostics and differentiation of its severity degree are determined. (image processing)« less

Describing litho-constrained layout by a high-resolution model filter

NASA Astrophysics Data System (ADS)

Tsai, Min-Chun

2008-05-01

A novel high-resolution model (HRM) filtering technique was proposed to describe litho-constrained layouts. Litho-constrained layouts are layouts that have difficulties to pattern or are highly sensitive to process-fluctuations under current lithography technologies. HRM applies a short-wavelength (or high NA) model simulation directly on the pre-OPC, original design layout to filter out low spatial-frequency regions, and retain high spatial-frequency components which are litho-constrained. Since no OPC neither mask-synthesis steps are involved, this new technique is highly efficient in run time and can be used in design stage to detect and fix litho-constrained patterns. This method has successfully captured all the hot-spots with less than 15% overshoots on a realistic 80 mm2 full-chip M1 layout in 65nm technology node. A step by step derivation of this HRM technique is presented in this paper.

Investigating the effect of previous treatments on wheat biomass over multiple spatial frequencies

NASA Astrophysics Data System (ADS)

Milne, A. E.; Castellanos, M. T.; Cartagena, M. C.; Tarquis, A. M.; Lark, R. M.

2010-09-01

In this study we use the maximum overlap discrete packet transform (MODWPT) to investigate residual effects on wheat biomass of fertigation treatments applied to a previous crop. The wheat crop covered nine subplots from a previous experiment on melon response to fertigation. Each subplot had previously received a different level of applied nitrogen. Many factors affect wheat biomass, causing it to vary at different spatial frequencies. We hypothesize that these will include residual effects from fertilizer application (at relatively low spatial frequencies) and the local influence of individual plants from the previous melon crop (at high frequency). To test this hypothesis we use the MODWPT to identify the dominant spatial frequencies of wheat biomass variation, and analyse the relationship to both the previous fertilizer application and the location of individual melon plants in the previous crop. The MODWPT is particularly appropriate for this because it allows us first to identify the key spatial frequencies in the wheat biomass objectively and to analyse them, and their relationship to hypothesized driving factors without any assumptions of uniformity (stationarity) of wheat-biomass variation. The results showed that the applied nitrogen dominated the wheat biomass response, and that there was a noticeable component of wheat-biomass variation at the spatial frequency that corresponds to the melon cropping. We expected wheat biomass to be negatively correlated with the position of melons in the previous crop, due to uptake of the applied nitrogen. The MODWPT, which allows us to detect changes in correlation between variables at different frequencies, showed that such a relationship was found across part of the experiment but not uniformly.

EMGAN: A computer program for time and frequency domain reduction of electromyographic data

NASA Technical Reports Server (NTRS)

Hursta, W. N.

1975-01-01

An experiment in electromyography utilizing surface electrode techniques was developed for the Apollo-Soyuz test project. This report describes the computer program, EMGAN, which was written to provide first order data reduction for the experiment. EMG signals are produced by the membrane depolarization of muscle fibers during a muscle contraction. Surface electrodes detect a spatially summated signal from a large number of muscle fibers commonly called an interference pattern. An interference pattern is usually so complex that analysis through signal morphology is extremely difficult if not impossible. It has become common to process EMG interference patterns in the frequency domain. Muscle fatigue and certain myopathic conditions are recognized through changes in muscle frequency spectra.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaznatcheev, K.; Bertwistle, D.; Cheng, C.

We have explored the capabilities of synchronous ('lock-in') point detection techniques to enhance the x-ray magnetic circular dichroism (XMCD) contrast in scanning x-ray transmission microscopy (STXM) of magnetic thin-film microstructures. Local absorption contrast, measured synchronously with low-amplitude (<10 Oe) and low-frequency (<200 hz) longitudinal fields perturbing the near-remanent magnetization state, reveal a strong spatial dependence of the response, with a roll-off in frequency response above 200 Hz. In this context, synchronous measurement affords us a basis for imaging the relation between energy loss and the sweeping rate. We speculate that the lock-in approach will be uniquely suited for detailing stochasticmore » and deterministic frequency-dependent events in the process of magnetization reversal.« less

Spatial Frequency Discrimination: Effects of Age, Reward, and Practice

PubMed Central

Peters, Judith Carolien

2017-01-01

Social interaction starts with perception of the world around you. This study investigated two fundamental issues regarding the development of discrimination of higher spatial frequencies, which are important building blocks of perception. Firstly, it mapped the typical developmental trajectory of higher spatial frequency discrimination. Secondly, it developed and validated a novel design that could be applied to improve atypically developed vision. Specifically, this study examined the effect of age and reward on task performance, practice effects, and motivation (i.e., number of trials completed) in a higher spatial frequency (reference frequency: 6 cycles per degree) discrimination task. We measured discrimination thresholds in children aged between 7 to 12 years and adults (N = 135). Reward was manipulated by presenting either positive reinforcement or punishment. Results showed a decrease in discrimination thresholds with age, thus revealing that higher spatial frequency discrimination continues to develop after 12 years of age. This development continues longer than previously shown for discrimination of lower spatial frequencies. Moreover, thresholds decreased during the run, indicating that discrimination abilities improved. Reward did not affect performance or improvement. However, in an additional group of 5–6 year-olds (N = 28) punishments resulted in the completion of fewer trials compared to reinforcements. In both reward conditions children aged 5–6 years completed only a fourth or half of the run (64 to 128 out of 254 trials) and were not motivated to continue. The design thus needs further adaptation before it can be applied to this age group. Children aged 7–12 years and adults completed the run, suggesting that the design is successful and motivating for children aged 7–12 years. This study thus presents developmental differences in higher spatial frequency discrimination thresholds. Furthermore, it presents a design that can be used in future developmental studies that require multiple stimulus presentations such as visual perceptual learning. PMID:28135272

Spatial Frequency Discrimination: Effects of Age, Reward, and Practice.

PubMed

van den Boomen, Carlijn; Peters, Judith Carolien

2017-01-01

Social interaction starts with perception of the world around you. This study investigated two fundamental issues regarding the development of discrimination of higher spatial frequencies, which are important building blocks of perception. Firstly, it mapped the typical developmental trajectory of higher spatial frequency discrimination. Secondly, it developed and validated a novel design that could be applied to improve atypically developed vision. Specifically, this study examined the effect of age and reward on task performance, practice effects, and motivation (i.e., number of trials completed) in a higher spatial frequency (reference frequency: 6 cycles per degree) discrimination task. We measured discrimination thresholds in children aged between 7 to 12 years and adults (N = 135). Reward was manipulated by presenting either positive reinforcement or punishment. Results showed a decrease in discrimination thresholds with age, thus revealing that higher spatial frequency discrimination continues to develop after 12 years of age. This development continues longer than previously shown for discrimination of lower spatial frequencies. Moreover, thresholds decreased during the run, indicating that discrimination abilities improved. Reward did not affect performance or improvement. However, in an additional group of 5-6 year-olds (N = 28) punishments resulted in the completion of fewer trials compared to reinforcements. In both reward conditions children aged 5-6 years completed only a fourth or half of the run (64 to 128 out of 254 trials) and were not motivated to continue. The design thus needs further adaptation before it can be applied to this age group. Children aged 7-12 years and adults completed the run, suggesting that the design is successful and motivating for children aged 7-12 years. This study thus presents developmental differences in higher spatial frequency discrimination thresholds. Furthermore, it presents a design that can be used in future developmental studies that require multiple stimulus presentations such as visual perceptual learning.

Image gathering and processing - Information and fidelity

NASA Technical Reports Server (NTRS)

Huck, F. O.; Fales, C. L.; Halyo, N.; Samms, R. W.; Stacy, K.

1985-01-01

In this paper we formulate and use information and fidelity criteria to assess image gathering and processing, combining optical design with image-forming and edge-detection algorithms. The optical design of the image-gathering system revolves around the relationship among sampling passband, spatial response, and signal-to-noise ratio (SNR). Our formulations of information, fidelity, and optimal (Wiener) restoration account for the insufficient sampling (i.e., aliasing) common in image gathering as well as for the blurring and noise that conventional formulations account for. Performance analyses and simulations for ordinary optical-design constraints and random scences indicate that (1) different image-forming algorithms prefer different optical designs; (2) informationally optimized designs maximize the robustness of optimal image restorations and lead to the highest-spatial-frequency channel (relative to the sampling passband) for which edge detection is reliable (if the SNR is sufficiently high); and (3) combining the informationally optimized design with a 3 by 3 lateral-inhibitory image-plane-processing algorithm leads to a spatial-response shape that approximates the optimal edge-detection response of (Marr's model of) human vision and thus reduces the data preprocessing and transmission required for machine vision.

Neural dynamics of motion processing and speed discrimination.

PubMed

Chey, J; Grossberg, S; Mingolla, E

1998-09-01

A neural network model of visual motion perception and speed discrimination is presented. The model shows how a distributed population code of speed tuning, that realizes a size-speed correlation, can be derived from the simplest mechanisms whereby activations of multiple spatially short-range filters of different size are transformed into speed-turned cell responses. These mechanisms use transient cell responses to moving stimuli, output thresholds that covary with filter size, and competition. These mechanisms are proposed to occur in the V1-->MT cortical processing stream. The model reproduces empirically derived speed discrimination curves and simulates data showing how visual speed perception and discrimination can be affected by stimulus contrast, duration, dot density and spatial frequency. Model motion mechanisms are analogous to mechanisms that have been used to model 3-D form and figure-ground perception. The model forms the front end of a larger motion processing system that has been used to simulate how global motion capture occurs, and how spatial attention is drawn to moving forms. It provides a computational foundation for an emerging neural theory of 3-D form and motion perception.

Image jitter enhances visual performance when spatial resolution is impaired.

PubMed

Watson, Lynne M; Strang, Niall C; Scobie, Fraser; Love, Gordon D; Seidel, Dirk; Manahilov, Velitchko

2012-09-06

Visibility of low-spatial frequency stimuli improves when their contrast is modulated at 5 to 10 Hz compared with stationary stimuli. Therefore, temporal modulations of visual objects could enhance the performance of low vision patients who primarily perceive images of low-spatial frequency content. We investigated the effect of retinal-image jitter on word recognition speed and facial emotion recognition in subjects with central visual impairment. Word recognition speed and accuracy of facial emotion discrimination were measured in volunteers with AMD under stationary and jittering conditions. Computer-driven and optoelectronic approaches were used to induce retinal-image jitter with duration of 100 or 166 ms and amplitude within the range of 0.5 to 2.6° visual angle. Word recognition speed was also measured for participants with simulated (Bangerter filters) visual impairment. Text jittering markedly enhanced word recognition speed for people with severe visual loss (101 ± 25%), while for those with moderate visual impairment, this effect was weaker (19 ± 9%). The ability of low vision patients to discriminate the facial emotions of jittering images improved by a factor of 2. A prototype of optoelectronic jitter goggles produced similar improvement in facial emotion discrimination. Word recognition speed in participants with simulated visual impairment was enhanced for interjitter intervals over 100 ms and reduced for shorter intervals. Results suggest that retinal-image jitter with optimal frequency and amplitude is an effective strategy for enhancing visual information processing in the absence of spatial detail. These findings will enable the development of novel tools to improve the quality of life of low vision patients.

Spatial and Temporal Patterns of Nitrification Rates in Forested Floodplain Wetland Soils of Upper Mississippi River Pool 8, Journal Article

EPA Science Inventory

Overbank flooding is thought to be a critical process controlling nitrogen retention and cycling. In this study we investigated the effects of season and flood frequency on soil nitrification rates at ten sites in forested floodplains of Upper Mississippi River, Pool 8...A rough ...

Audio-visual synchrony and feature-selective attention co-amplify early visual processing.

PubMed

Keitel, Christian; Müller, Matthias M

2016-05-01

Our brain relies on neural mechanisms of selective attention and converging sensory processing to efficiently cope with rich and unceasing multisensory inputs. One prominent assumption holds that audio-visual synchrony can act as a strong attractor for spatial attention. Here, we tested for a similar effect of audio-visual synchrony on feature-selective attention. We presented two superimposed Gabor patches that differed in colour and orientation. On each trial, participants were cued to selectively attend to one of the two patches. Over time, spatial frequencies of both patches varied sinusoidally at distinct rates (3.14 and 3.63 Hz), giving rise to pulse-like percepts. A simultaneously presented pure tone carried a frequency modulation at the pulse rate of one of the two visual stimuli to introduce audio-visual synchrony. Pulsed stimulation elicited distinct time-locked oscillatory electrophysiological brain responses. These steady-state responses were quantified in the spectral domain to examine individual stimulus processing under conditions of synchronous versus asynchronous tone presentation and when respective stimuli were attended versus unattended. We found that both, attending to the colour of a stimulus and its synchrony with the tone, enhanced its processing. Moreover, both gain effects combined linearly for attended in-sync stimuli. Our results suggest that audio-visual synchrony can attract attention to specific stimulus features when stimuli overlap in space.

Towards Understanding the Timing and Frequency of Rain-on-Snow (ROS) Events in Alaska

NASA Astrophysics Data System (ADS)

Pan, C.; Kirchner, P. B.; Kimball, J. S.; Kim, Y.; Kamp, U.

2017-12-01

Rain-on-snow (ROS) events affect ecosystem processes at multiple spatial and temporal scales including hydrology, carbon cycling, wildlife movement and human transportation and result in marked changes to snowpack processes including enhanced snow melt, surface albedo and energy balance. Changes in the surface structure of the snowpack are visible through optical remote sensing and changes in the relative content and distribution of water, air and ice in the snowpack are detectable using passive microwave remote sensing. This project aims to develop ROS products to elucidate changes in frequency and distribution in ROS events using satellite data products derived from both optical and passive microwave satellite records. To detect ROS events, we use downscaled brightness temperature measurements derived from vertical and horizontal polarizations at 19 and 37 GHz from the Advanced Microwave Scanning Radiometer (AMSR-E/2) passive microwave satellites. Preliminary results indicate an overall classification accuracy of 77.6% relative to in situ weather observations including surface air temperature, precipitation, and snow depth. ROS events are spatially distributed largely to elevations below 500 m and occur most frequently on northern to western aspects in addition to southeastern. Regional ROS hot spots occur in southwest Alaska characterized by warmer climates and transient snowcover. The seasonal timing of ROS events indicates increasing frequency during the fall and spring months.

Extremely low frequency (ELF) stray magnetic fields of laboratory equipment: a possible co-exposure conducting experiments on cell cultures.

PubMed

Gresits, Iván; Necz, Péter Pál; Jánossy, Gábor; Thuróczy, György

2015-09-01

Measurements of extremely low frequency (ELF) magnetic fields were conducted in the environment of commercial laboratory equipment in order to evaluate the possible co-exposure during the experimental processes on cell cultures. Three types of device were evaluated: a cell culture CO2 incubator, a thermostatic water bath and a laboratory shaker table. These devices usually have electric motors, heating wires and electronic control systems, therefore may expose the cell cultures to undesirable ELF stray magnetic fields. Spatial distributions of magnetic field time domain signal waveform and frequency spectral analysis (FFT) were processed. Long- and short-term variation of stray magnetic field was also evaluated under normal use of investigated laboratory devices. The results show that the equipment under test may add a considerable ELF magnetic field to the ambient environmental magnetic field or to the intentional exposure to ELF, RF or other physical/chemical agents. The maximum stray magnetic fields were higher than 3 µT, 20 µT and 75 µT in the CO2 incubator, in water bath and on the laboratory shaker table, respectively, with high variation of spatial distribution and time domain. Our investigation emphasizes possible confounding factors conducting cell culture studies related to low-level ELF-EMF exposure due to the existing stray magnetic fields in the ambient environment of laboratory equipment.

Tampered Region Localization of Digital Color Images Based on JPEG Compression Noise

NASA Astrophysics Data System (ADS)

Wang, Wei; Dong, Jing; Tan, Tieniu

With the availability of various digital image edit tools, seeing is no longer believing. In this paper, we focus on tampered region localization for image forensics. We propose an algorithm which can locate tampered region(s) in a lossless compressed tampered image when its unchanged region is output of JPEG decompressor. We find the tampered region and the unchanged region have different responses for JPEG compression. The tampered region has stronger high frequency quantization noise than the unchanged region. We employ PCA to separate different spatial frequencies quantization noises, i.e. low, medium and high frequency quantization noise, and extract high frequency quantization noise for tampered region localization. Post-processing is involved to get final localization result. The experimental results prove the effectiveness of our proposed method.

Right Hemispatial Neglect: Frequency and Characterization Following Acute Left Hemisphere Stroke

ERIC Educational Resources Information Center

Kleinman, Jonathan T.; Newhart, Melissa; Davis, Cameron; Heidler-Gary, Jennifer; Gottesman, Rebecca F.; Hillis, Argye E.

2007-01-01

The frequency of various types of unilateral spatial neglect and associated areas of neural dysfunction after left hemisphere stroke are not well characterized. Unilateral spatial neglect (USN) in distinct spatial reference frames have been identified after acute right, but not left hemisphere stroke. We studied 47 consecutive right handed…

Stimulus Type, Level of Categorization, and Spatial-Frequencies Utilization: Implications for Perceptual Categorization Hierarchies

ERIC Educational Resources Information Center

Harel, Assaf; Bentin, Shlomo

2009-01-01

The type of visual information needed for categorizing faces and nonface objects was investigated by manipulating spatial frequency scales available in the image during a category verification task addressing basic and subordinate levels. Spatial filtering had opposite effects on faces and airplanes that were modulated by categorization level. The…

Brief Report: Developing Spatial Frequency Biases for Face Recognition in Autism and Williams Syndrome

ERIC Educational Resources Information Center

Leonard, Hayley C.; Annaz, Dagmara; Karmiloff-Smith, Annette; Johnson, Mark H.

2011-01-01

The current study investigated whether contrasting face recognition abilities in autism and Williams syndrome could be explained by different spatial frequency biases over developmental time. Typically-developing children and groups with Williams syndrome and autism were asked to recognise faces in which low, middle and high spatial frequency…

Effects of Genetic Drift and Gene Flow on the Selective Maintenance of Genetic Variation

PubMed Central

Star, Bastiaan; Spencer, Hamish G.

2013-01-01

Explanations for the genetic variation ubiquitous in natural populations are often classified by the population–genetic processes they emphasize: natural selection or mutation and genetic drift. Here we investigate models that incorporate all three processes in a spatially structured population, using what we call a construction approach, simulating finite populations under selection that are bombarded with a steady stream of novel mutations. As expected, the amount of genetic variation compared to previous models that ignored the stochastic effects of drift was reduced, especially for smaller populations and when spatial structure was most profound. By contrast, however, for higher levels of gene flow and larger population sizes, the amount of genetic variation found after many generations was greater than that in simulations without drift. This increased amount of genetic variation is due to the introduction of slightly deleterious alleles by genetic drift and this process is more efficient when migration load is higher. The incorporation of genetic drift also selects for fitness sets that exhibit allele-frequency equilibria with larger domains of attraction: they are “more stable.” Moreover, the finiteness of populations strongly influences levels of local adaptation, selection strength, and the proportion of allele-frequency vectors that can be distinguished from the neutral expectation. PMID:23457235

Insensitivity to Fearful Emotion for Early ERP Components in High Autistic Tendency Is Associated with Lower Magnocellular Efficiency.

PubMed

Burt, Adelaide; Hugrass, Laila; Frith-Belvedere, Tash; Crewther, David

2017-01-01

Low spatial frequency (LSF) visual information is extracted rapidly from fearful faces, suggesting magnocellular involvement. Autistic phenotypes demonstrate altered magnocellular processing, which we propose contributes to a decreased P100 evoked response to LSF fearful faces. Here, we investigated whether rapid processing of fearful facial expressions differs for groups of neurotypical adults with low and high scores on the Autistic Spectrum Quotient (AQ). We created hybrid face stimuli with low and high spatial frequency filtered, fearful, and neutral expressions. Fearful faces produced higher amplitude P100 responses than neutral faces in the low AQ group, particularly when the hybrid face contained a LSF fearful expression. By contrast, there was no effect of fearful expression on P100 amplitude in the high AQ group. Consistent with evidence linking magnocellular differences with autistic personality traits, our non-linear VEP results showed that the high AQ group had higher amplitude K2.1 responses than the low AQ group, which is indicative of less efficient magnocellular recovery. Our results suggest that magnocellular LSF processing of a human face may be the initial visual cue used to rapidly and automatically detect fear, but that this cue functions atypically in those with high autistic tendency.

High-latitude distributions of plasma waves and spatial irregularities from DE 2 alternating current electric field observations

NASA Technical Reports Server (NTRS)

Heppner, J. P.; Liebrecht, M. C.; Maynard, N. C.; Pfaff, R. F.

1993-01-01

The high-latitude spatial distributions of average signal intensities in 12 frequency channels between 4 Hz and 512 kHz as measured by the ac electric field spectrometers on the DE-2 spacecraft are analyzed for 18 mo of measurements. In MLT-INL (magnetic local time-invariant latitude) there are three distinct distributions that can be identified with 4-512 Hz signals from spatial irregularities and Alfven waves, 256-Hz to 4.1-kHz signals from ELF hiss, and 4.1-64 kHz signals from VLF auroral hiss, respectively. Overlap between ELF hiss and spatial irregularity signals occurs in the 256-512 Hz band. VLF hiss signals extend downward in frequency into the 1.0-4.1 kHz band and upward into the frequency range 128-512 kHz. The distinctly different spatial distribution patterns for the three bands, 4-256 Hz, 512-1204 Hz, and 4.1-64 kHz, indicate a lack of any causal relationships between VLF hiss, ELF hiss, and lower-frequency signals from spatial irregularities and Alfven waves.

Neurons in cat V1 show significant clustering by degree of tuning

PubMed Central

Ziskind, Avi J.; Emondi, Al A.; Kurgansky, Andrei V.; Rebrik, Sergei P.

2015-01-01

Neighboring neurons in cat primary visual cortex (V1) have similar preferred orientation, direction, and spatial frequency. How diverse is their degree of tuning for these properties? To address this, we used single-tetrode recordings to simultaneously isolate multiple cells at single recording sites and record their responses to flashed and drifting gratings of multiple orientations, spatial frequencies, and, for drifting gratings, directions. Orientation tuning width, spatial frequency tuning width, and direction selectivity index (DSI) all showed significant clustering: pairs of neurons recorded at a single site were significantly more similar in each of these properties than pairs of neurons from different recording sites. The strength of the clustering was generally modest. The percent decrease in the median difference between pairs from the same site, relative to pairs from different sites, was as follows: for different measures of orientation tuning width, 29–35% (drifting gratings) or 15–25% (flashed gratings); for DSI, 24%; and for spatial frequency tuning width measured in octaves, 8% (drifting gratings). The clusterings of all of these measures were much weaker than for preferred orientation (68% decrease) but comparable to that seen for preferred spatial frequency in response to drifting gratings (26%). For the above properties, little difference in clustering was seen between simple and complex cells. In studies of spatial frequency tuning to flashed gratings, strong clustering was seen among simple-cell pairs for tuning width (70% decrease) and preferred frequency (71% decrease), whereas no clustering was seen for simple-complex or complex-complex cell pairs. PMID:25652921

Design of an integrated aerial image sensor

NASA Astrophysics Data System (ADS)

Xue, Jing; Spanos, Costas J.

2005-05-01

The subject of this paper is a novel integrated aerial image sensor (IAIS) system suitable for integration within the surface of an autonomous test wafer. The IAIS could be used as a lithography processing monitor, affording a "wafer's eye view" of the process, and therefore facilitating advanced process control and diagnostics without integrating (and dedicating) the sensor to the processing equipment. The IAIS is composed of an aperture mask and an array of photo-detectors. In order to retrieve nanometer scale resolution of the aerial image with a practical photo-detector pixel size, we propose a design of an aperture mask involving a series of spatial phase "moving" aperture groups. We demonstrate a design example aimed at the 65nm technology node through TEMPEST simulation. The optimized, key design parameters include an aperture width in the range of 30nm, aperture thickness in the range of 70nm, and offer a spatial resolution of about 5nm, all with comfortable fabrication tolerances. Our preliminary simulation work indicates the possibility of the IAIS being applied to the immersion lithography. A bench-top far-field experiment verifies that our approach of the spatial frequency down-shift through forming large Moire patterns is feasible.

Effect of wafer geometry on lithography chucking processes

NASA Astrophysics Data System (ADS)

Turner, Kevin T.; Sinha, Jaydeep K.

2015-03-01

Wafer flatness during exposure in lithography tools is critical and is becoming more important as feature sizes in devices shrink. While chucks are used to support and flatten the wafer during exposure, it is essential that wafer geometry be controlled as well. Thickness variations of the wafer and high-frequency wafer shape components can lead to poor flatness of the chucked wafer and ultimately patterning problems, such as defocus errors. The objective of this work is to understand how process-induced wafer geometry, resulting from deposited films with non-uniform stress, can lead to high-frequency wafer shape variations that prevent complete chucking in lithography scanners. In this paper, we discuss both the acceptable limits of wafer shape that permit complete chucking to be achieved, and how non-uniform residual stresses in films, either due to patterning or process non-uniformity, can induce high spatial frequency wafer shape components that prevent chucking. This paper describes mechanics models that relate non-uniform film stress to wafer shape and presents results for two example cases. The models and results can be used as a basis for establishing control strategies for managing process-induced wafer geometry in order to avoid wafer flatness-induced errors in lithography processes.

POD and PPP with multi-frequency processing

NASA Astrophysics Data System (ADS)

Roldán, Pedro; Navarro, Pedro; Rodríguez, Daniel; Rodríguez, Irma

2017-04-01

Precise Orbit Determination (POD) and Precise Point Positioning (PPP) are methods for estimating the orbits and clocks of GNSS satellites and the precise positions and clocks of user receivers. These methods are traditionally based on processing the ionosphere-free combination. With this combination, the delay introduced in the signal when passing through the ionosphere is removed, taking advantage of the dependency of this delay with the square of the frequency. It is also possible to process the individual frequencies, but in this case it is needed to properly model the ionospheric delay. This modelling is usually very challenging, as the electron content in the ionosphere experiences important temporal and spatial variations. These two options define the two main kinds of processing: the dual-frequency ionosphere-free processing, typically used in the POD and in certain applications of PPP, and the single-frequency processing with estimation or modelisation of the ionosphere, mostly used in the PPP processing. In magicGNSS, a software tool developed by GMV for POD and PPP, a hybrid approach has been implemented. This approach combines observations from any number of individual frequencies and any number of ionosphere-free combinations of these frequencies. In such a way, the observations of ionosphere-free combination allow a better estimation of positions and orbits, while the inclusion of observations from individual frequencies allows to estimate the ionospheric delay and to reduce the noise of the solution. It is also possible to include other kind of combinations, such as geometry-free combination, instead of processing individual frequencies. The joint processing of all the frequencies for all the constellations requires both the estimation or modelisation of ionospheric delay and the estimation of inter-frequency biases. The ionospheric delay can be estimated from the single-frequency or dual-frequency geometry-free observations, but it is also possible to use a-priori information based on ionospheric models, on external estimations and on the expected behavior of the ionosphere. The inter-frequency biases appear because the delay of the signal inside the transmitter and the receiver strongly depends on its frequency. However, it is possible to include constraints in the estimator regarding these delays, assuming small variations over time. By using different types of combinations, all the available information from GNSS systems can be included in the processing. This is especially interesting for the case of Galileo satellites, which transmit in several frequencies, and the GPS IIF satellites, which transmit in L5 in addition to the traditional L1 and L2. Several experiments have been performed, to assess the improvement on performance of POD and PPP when using all the constellations and all the available frequencies for each constellation. This paper describes the new approach of multi-frequency processing, including the estimation of biases and ionospheric delays impacting on GNSS observations, and presents the results of the performed experimentation activities to assess the benefits in POD and PPP algorithms.

Spatial resolution dependence on spectral frequency in human speech cortex electrocorticography.

PubMed

Muller, Leah; Hamilton, Liberty S; Edwards, Erik; Bouchard, Kristofer E; Chang, Edward F

2016-10-01

Electrocorticography (ECoG) has become an important tool in human neuroscience and has tremendous potential for emerging applications in neural interface technology. Electrode array design parameters are outstanding issues for both research and clinical applications, and these parameters depend critically on the nature of the neural signals to be recorded. Here, we investigate the functional spatial resolution of neural signals recorded at the human cortical surface. We empirically derive spatial spread functions to quantify the shared neural activity for each frequency band of the electrocorticogram. Five subjects with high-density (4 mm center-to-center spacing) ECoG grid implants participated in speech perception and production tasks while neural activity was recorded from the speech cortex, including superior temporal gyrus, precentral gyrus, and postcentral gyrus. The cortical surface field potential was decomposed into traditional EEG frequency bands. Signal similarity between electrode pairs for each frequency band was quantified using a Pearson correlation coefficient. The correlation of neural activity between electrode pairs was inversely related to the distance between the electrodes; this relationship was used to quantify spatial falloff functions for cortical subdomains. As expected, lower frequencies remained correlated over larger distances than higher frequencies. However, both the envelope and phase of gamma and high gamma frequencies (30-150 Hz) are largely uncorrelated (<90%) at 4 mm, the smallest spacing of the high-density arrays. Thus, ECoG arrays smaller than 4 mm have significant promise for increasing signal resolution at high frequencies, whereas less additional gain is achieved for lower frequencies. Our findings quantitatively demonstrate the dependence of ECoG spatial resolution on the neural frequency of interest. We demonstrate that this relationship is consistent across patients and across cortical areas during activity.

Spatial resolution dependence on spectral frequency in human speech cortex electrocorticography

NASA Astrophysics Data System (ADS)

Muller, Leah; Hamilton, Liberty S.; Edwards, Erik; Bouchard, Kristofer E.; Chang, Edward F.

2016-10-01

Objective. Electrocorticography (ECoG) has become an important tool in human neuroscience and has tremendous potential for emerging applications in neural interface technology. Electrode array design parameters are outstanding issues for both research and clinical applications, and these parameters depend critically on the nature of the neural signals to be recorded. Here, we investigate the functional spatial resolution of neural signals recorded at the human cortical surface. We empirically derive spatial spread functions to quantify the shared neural activity for each frequency band of the electrocorticogram. Approach. Five subjects with high-density (4 mm center-to-center spacing) ECoG grid implants participated in speech perception and production tasks while neural activity was recorded from the speech cortex, including superior temporal gyrus, precentral gyrus, and postcentral gyrus. The cortical surface field potential was decomposed into traditional EEG frequency bands. Signal similarity between electrode pairs for each frequency band was quantified using a Pearson correlation coefficient. Main results. The correlation of neural activity between electrode pairs was inversely related to the distance between the electrodes; this relationship was used to quantify spatial falloff functions for cortical subdomains. As expected, lower frequencies remained correlated over larger distances than higher frequencies. However, both the envelope and phase of gamma and high gamma frequencies (30-150 Hz) are largely uncorrelated (<90%) at 4 mm, the smallest spacing of the high-density arrays. Thus, ECoG arrays smaller than 4 mm have significant promise for increasing signal resolution at high frequencies, whereas less additional gain is achieved for lower frequencies. Significance. Our findings quantitatively demonstrate the dependence of ECoG spatial resolution on the neural frequency of interest. We demonstrate that this relationship is consistent across patients and across cortical areas during activity.

Investigating the Small-Scale Spatial Variabilty of Precipitable Water Vapor by Adding Single-Frequency Receivers into an Existing Dual-Frequency Receiver Network

NASA Astrophysics Data System (ADS)

Krietemeyer, Andreas; ten Veldhuis, Marie-claire; van de Giesen, Nick

2017-04-01

Exploiting GNSS signal delays is one possibility to obtain Precipitable Water Vapor (PWV) estimates in the atmosphere. The technique is well known since the early 1990s and by now an established method in the meteorological community. The data is crucial for weather forecasting and its assimilation into numerical weather forecasting models is a topic of ongoing research. However, the spatial resolution of ground based GNSS receivers is usually low, in the order of tens of kilometres. Since severe weather events such as convective storms can be concentrated in spatial extent, existing GNSS networks are often not sufficient to retrieve small scale PWV fluctuations and need to be densified. For economic reasons, the use of low-cost single-frequency receivers is a promising solution. In this study, we will deploy a network of single-frequency receivers to densify an existing dual-frequency network in order to investigate the spatial and temporal PWV variations. We demonstrate a test network consisting of four single-frequency receivers in the Rotterdam area (Netherlands). In order to eliminate the delay caused by the ionosphere, the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) is applied, using a surrounding dual-frequency network distributed over a radius of approximately 25 km. With the synthesized L2 frequency, the tropospheric delays are estimated using the Precise Point Positioning (PPP) strategy and International GNSS Service (IGS) final orbits. The PWV time series are validated by a comparison of a collocated single-frequency and a dual-frequency receiver. The time series themselves form the basis for potential further studies like data assimilation into numerical weather models and GNSS tomography to study the impact of the increased spatial resolution on local heavy rain forecast.

Semantic word category processing in semantic dementia and posterior cortical atrophy.

PubMed

Shebani, Zubaida; Patterson, Karalyn; Nestor, Peter J; Diaz-de-Grenu, Lara Z; Dawson, Kate; Pulvermüller, Friedemann

2017-08-01

There is general agreement that perisylvian language cortex plays a major role in lexical and semantic processing; but the contribution of additional, more widespread, brain areas in the processing of different semantic word categories remains controversial. We investigated word processing in two groups of patients whose neurodegenerative diseases preferentially affect specific parts of the brain, to determine whether their performance would vary as a function of semantic categories proposed to recruit those brain regions. Cohorts with (i) Semantic Dementia (SD), who have anterior temporal-lobe atrophy, and (ii) Posterior Cortical Atrophy (PCA), who have predominantly parieto-occipital atrophy, performed a lexical decision test on words from five different lexico-semantic categories: colour (e.g., yellow), form (oval), number (seven), spatial prepositions (under) and function words (also). Sets of pseudo-word foils matched the target words in length and bi-/tri-gram frequency. Word-frequency was matched between the two visual word categories (colour and form) and across the three other categories (number, prepositions, and function words). Age-matched healthy individuals served as controls. Although broad word processing deficits were apparent in both patient groups, the deficit was strongest for colour words in SD and for spatial prepositions in PCA. The patterns of performance on the lexical decision task demonstrate (a) general lexicosemantic processing deficits in both groups, though more prominent in SD than in PCA, and (b) differential involvement of anterior-temporal and posterior-parietal cortex in the processing of specific semantic categories of words. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Attention Modifies Spatial Resolution According to Task Demands.

PubMed

Barbot, Antoine; Carrasco, Marisa

2017-03-01

How does visual attention affect spatial resolution? In texture-segmentation tasks, exogenous (involuntary) attention automatically increases resolution at the attended location, which improves performance where resolution is too low (at the periphery) but impairs performance where resolution is already too high (at central locations). Conversely, endogenous (voluntary) attention improves performance at all eccentricities, which suggests a more flexible mechanism. Here, using selective adaptation to spatial frequency, we investigated the mechanism by which endogenous attention benefits performance in resolution tasks. Participants detected a texture target that could appear at several eccentricities. Adapting to high or low spatial frequencies selectively affected performance in a manner consistent with changes in resolution. Moreover, adapting to high, but not low, frequencies mitigated the attentional benefit at central locations where resolution was too high; this shows that attention can improve performance by decreasing resolution. Altogether, our results indicate that endogenous attention benefits performance by modulating the contribution of high-frequency information in order to flexibly adjust spatial resolution according to task demands.

Attention Modifies Spatial Resolution According to Task Demands

PubMed Central

Barbot, Antoine; Carrasco, Marisa

2017-01-01

How does visual attention affect spatial resolution? In texture-segmentation tasks, exogenous (involuntary) attention automatically increases resolution at the attended location, which improves performance where resolution is too low (at the periphery) but impairs performance where resolution is already too high (at central locations). Conversely, endogenous (voluntary) attention improves performance at all eccentricities, which suggests a more flexible mechanism. Here, using selective adaptation to spatial frequency, we investigated the mechanism by which endogenous attention benefits performance in resolution tasks. Participants detected a texture target that could appear at several eccentricities. Adapting to high or low spatial frequencies selectively affected performance in a manner consistent with changes in resolution. Moreover, adapting to high, but not low, frequencies mitigated the attentional benefit at central locations where resolution was too high; this shows that attention can improve performance by decreasing resolution. Altogether, our results indicate that endogenous attention benefits performance by modulating the contribution of high-frequency information in order to flexibly adjust spatial resolution according to task demands. PMID:28118103

Method to optimize patch size based on spatial frequency response in image rendering of the light field

NASA Astrophysics Data System (ADS)

Zhang, Wei; Wang, Yanan; Zhu, Zhenhao; Su, Jinhui

2018-05-01

A focused plenoptic camera can effectively transform angular and spatial information to yield a refocused rendered image with high resolution. However, choosing a proper patch size poses a significant problem for the image-rendering algorithm. By using a spatial frequency response measurement, a method to obtain a suitable patch size is presented. By evaluating the spatial frequency response curves, the optimized patch size can be obtained quickly and easily. Moreover, the range of depth over which images can be rendered without artifacts can be estimated. Experiments show that the results of the image rendered based on frequency response measurement are in accordance with the theoretical calculation, which indicates that this is an effective way to determine the patch size. This study may provide support to light-field image rendering.

Visual sensitivity for luminance and chromatic stimuli during the execution of smooth pursuit and saccadic eye movements.

PubMed

Braun, Doris I; Schütz, Alexander C; Gegenfurtner, Karl R

2017-07-01

Visual sensitivity is dynamically modulated by eye movements. During saccadic eye movements, sensitivity is reduced selectively for low-spatial frequency luminance stimuli and largely unaffected for high-spatial frequency luminance and chromatic stimuli (Nature 371 (1994), 511-513). During smooth pursuit eye movements, sensitivity for low-spatial frequency luminance stimuli is moderately reduced while sensitivity for chromatic and high-spatial frequency luminance stimuli is even increased (Nature Neuroscience, 11 (2008), 1211-1216). Since these effects are at least partly of different polarity, we investigated the combined effects of saccades and smooth pursuit on visual sensitivity. For the time course of chromatic sensitivity, we found that detection rates increased slightly around pursuit onset. During saccades to static and moving targets, detection rates dropped briefly before the saccade and reached a minimum at saccade onset. This reduction of chromatic sensitivity was present whenever a saccade was executed and it was not modified by subsequent pursuit. We also measured contrast sensitivity for flashed high- and low-spatial frequency luminance and chromatic stimuli during saccades and pursuit. During saccades, the reduction of contrast sensitivity was strongest for low-spatial frequency luminance stimuli (about 90%). However, a significant reduction was also present for chromatic stimuli (about 58%). Chromatic sensitivity was increased during smooth pursuit (about 12%). These results suggest that the modulation of visual sensitivity during saccades and smooth pursuit is more complex than previously assumed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Clinical skin imaging using color spatial frequency domain imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Yang, Bin; Lesicko, John; Moy, Austin J.; Reichenberg, Jason; Tunnell, James W.

2016-02-01

Skin diseases are typically associated with underlying biochemical and structural changes compared with normal tissues, which alter the optical properties of the skin lesions, such as tissue absorption and scattering. Although widely used in dermatology clinics, conventional dermatoscopes don't have the ability to selectively image tissue absorption and scattering, which may limit its diagnostic power. Here we report a novel clinical skin imaging technique called color spatial frequency domain imaging (cSFDI) which enhances contrast by rendering color spatial frequency domain (SFD) image at high spatial frequency. Moreover, by tuning spatial frequency, we can obtain both absorption weighted and scattering weighted images. We developed a handheld imaging system specifically for clinical skin imaging. The flexible configuration of the system allows for better access to skin lesions in hard-to-reach regions. A total of 48 lesions from 31 patients were imaged under 470nm, 530nm and 655nm illumination at a spatial frequency of 0.6mm^(-1). The SFD reflectance images at 470nm, 530nm and 655nm were assigned to blue (B), green (G) and red (R) channels to render a color SFD image. Our results indicated that color SFD images at f=0.6mm-1 revealed properties that were not seen in standard color images. Structural features were enhanced and absorption features were reduced, which helped to identify the sources of the contrast. This imaging technique provides additional insights into skin lesions and may better assist clinical diagnosis.

Attempting to physically explain space-time correlation of extremes

NASA Astrophysics Data System (ADS)

Bernardara, Pietro; Gailhard, Joel

2010-05-01

Spatial and temporal clustering of hydro-meteorological extreme events is scientific evidence. Moreover, the statistical parameters characterizing their local frequencies of occurrence show clear spatial patterns. Thus, in order to robustly assess the hydro-meteorological hazard, statistical models need to be able to take into account spatial and temporal dependencies. Statistical models considering long term correlation for quantifying and qualifying temporal and spatial dependencies are available, such as multifractal approach. Furthermore, the development of regional frequency analysis techniques allows estimating the frequency of occurrence of extreme events taking into account spatial patterns on the extreme quantiles behaviour. However, in order to understand the origin of spatio-temporal clustering, an attempt to find physical explanation should be done. Here, some statistical evidences of spatio-temporal correlation and spatial patterns of extreme behaviour are given on a large database of more than 400 rainfall and discharge series in France. In particular, the spatial distribution of multifractal and Generalized Pareto distribution parameters shows evident correlation patterns in the behaviour of frequency of occurrence of extremes. It is then shown that the identification of atmospheric circulation pattern (weather types) can physically explain the temporal clustering of extreme rainfall events (seasonality) and the spatial pattern of the frequency of occurrence. Moreover, coupling this information with the hydrological modelization of a watershed (as in the Schadex approach) an explanation of spatio-temporal distribution of extreme discharge can also be provided. We finally show that a hydro-meteorological approach (as the Schadex approach) can explain and take into account space and time dependencies of hydro-meteorological extreme events.

Temporal Instabilities in Amblyopic Perception: A Quantitative Approach.

PubMed

Thiel, Aylin; Iftime, Adrian

2016-04-01

The purpose of this study is to quantify the temporal characteristics of spatial misperceptions in human amblyopia. Twenty-two adult participants with strabismus, strabismic, anisometropic, or mixed amblyopia were asked to describe their subjective percept of static geometrical patterns with different spatial frequencies and shapes, as seen with their non-dominant eye. We generated digital reconstructions of their perception (static images or movies) that were subsequently validated by the subjects using consecutive matching sessions. We calculated the Shannon entropy variation in time for each recorded movie, as a measure of temporal instability. Nineteen of the 22 subjects perceived temporal instabilities that can be broadly classified in two categories. We found that the average frequency of the perceived temporal instabilities is ∼1 Hz. The stimuli with higher spatial frequencies yielded more often temporally unstable perceptions with higher frequencies. We suggest that type and amount of temporal instabilities in amblyopic vision are correlated with the etiology and spatial frequency of the stimulus.

Complex-valued time-series correlation increases sensitivity in FMRI analysis.

PubMed

Kociuba, Mary C; Rowe, Daniel B

2016-07-01

To develop a linear matrix representation of correlation between complex-valued (CV) time-series in the temporal Fourier frequency domain, and demonstrate its increased sensitivity over correlation between magnitude-only (MO) time-series in functional MRI (fMRI) analysis. The standard in fMRI is to discard the phase before the statistical analysis of the data, despite evidence of task related change in the phase time-series. With a real-valued isomorphism representation of Fourier reconstruction, correlation is computed in the temporal frequency domain with CV time-series data, rather than with the standard of MO data. A MATLAB simulation compares the Fisher-z transform of MO and CV correlations for varying degrees of task related magnitude and phase amplitude change in the time-series. The increased sensitivity of the complex-valued Fourier representation of correlation is also demonstrated with experimental human data. Since the correlation description in the temporal frequency domain is represented as a summation of second order temporal frequencies, the correlation is easily divided into experimentally relevant frequency bands for each voxel's temporal frequency spectrum. The MO and CV correlations for the experimental human data are analyzed for four voxels of interest (VOIs) to show the framework with high and low contrast-to-noise ratios in the motor cortex and the supplementary motor cortex. The simulation demonstrates the increased strength of CV correlations over MO correlations for low magnitude contrast-to-noise time-series. In the experimental human data, the MO correlation maps are noisier than the CV maps, and it is more difficult to distinguish the motor cortex in the MO correlation maps after spatial processing. Including both magnitude and phase in the spatial correlation computations more accurately defines the correlated left and right motor cortices. Sensitivity in correlation analysis is important to preserve the signal of interest in fMRI data sets with high noise variance, and avoid excessive processing induced correlation. Copyright © 2016 Elsevier Inc. All rights reserved.

Frequency-dependent tACS modulation of BOLD signal during rhythmic visual stimulation.

PubMed

Chai, Yuhui; Sheng, Jingwei; Bandettini, Peter A; Gao, Jia-Hong

2018-05-01

Transcranial alternating current stimulation (tACS) has emerged as a promising tool for modulating cortical oscillations. In previous electroencephalogram (EEG) studies, tACS has been found to modulate brain oscillatory activity in a frequency-specific manner. However, the spatial distribution and hemodynamic response for this modulation remains poorly understood. Functional magnetic resonance imaging (fMRI) has the advantage of measuring neuronal activity in regions not only below the tACS electrodes but also across the whole brain with high spatial resolution. Here, we measured fMRI signal while applying tACS to modulate rhythmic visual activity. During fMRI acquisition, tACS at different frequencies (4, 8, 16, and 32 Hz) was applied along with visual flicker stimulation at 8 and 16 Hz. We analyzed the blood-oxygen-level-dependent (BOLD) signal difference between tACS-ON vs tACS-OFF, and different frequency combinations (e.g., 4 Hz tACS, 8 Hz flicker vs 8 Hz tACS, 8 Hz flicker). We observed significant tACS modulation effects on BOLD responses when the tACS frequency matched the visual flicker frequency or the second harmonic frequency. The main effects were predominantly seen in regions that were activated by the visual task and targeted by the tACS current distribution. These findings bridge different scientific domains of tACS research and demonstrate that fMRI could localize the tACS effect on stimulus-induced brain rhythms, which could lead to a new approach for understanding the high-level cognitive process shaped by the ongoing oscillatory signal. © 2018 Wiley Periodicals, Inc.

Research on the EDM Technology for Micro-holes at Complex Spatial Locations

NASA Astrophysics Data System (ADS)

Y Liu, J.; Guo, J. M.; Sun, D. J.; Cai, Y. H.; Ding, L. T.; Jiang, H.

2017-12-01

For the demands on machining micro-holes at complex spatial location, several key technical problems are conquered such as micro-Electron Discharge Machining (micro-EDM) power supply system’s development, the host structure’s design and machining process technical. Through developing low-voltage power supply circuit, high-voltage circuit, micro and precision machining circuit and clearance detection system, the narrow pulse and high frequency six-axis EDM machining power supply system is developed to meet the demands on micro-hole discharging machining. With the method of combining the CAD structure design, CAE simulation analysis, modal test, ODS (Operational Deflection Shapes) test and theoretical analysis, the host construction and key axes of the machine tool are optimized to meet the position demands of the micro-holes. Through developing the special deionized water filtration system to make sure that the machining process is stable enough. To verify the machining equipment and processing technical developed in this paper through developing the micro-hole’s processing flow and test on the real machine tool. As shown in the final test results: the efficient micro-EDM machining pulse power supply system, machine tool host system, deionized filtration system and processing method developed in this paper meet the demands on machining micro-holes at complex spatial locations.

[Imprinting as a mechanism of information memorizing in the adult BALB/c mice].

PubMed

Nikol'skaia, K A; Berezhnoĭ, D S

2011-09-01

Study of spatial learning in adult BALB/c mice revealed that a short exposition to the environment (from 3 to 8 minutes) could be enough for spatial information to be fixed in the long-term memory, and affected subsequent learning process in the new environment. Control group, learning in the same maze, followed the "shortest path" principle during formation of the optimal food-obtaining habit. Experimental animals, learning in a slightly changed environment, were unable to apply this rule due to persistent coupling of the new spatial information with the old memory traces which led to constant errors. The obtained effect was observed during the whole learning period and depended neither on frequency nor on interval of repetition during the initial information acquisition. The obtained data testify that memorizing in adult state share the properties with the imprinting process inherent in the early ontogeny. The memory fixation on all development stages seems to be based on a universal mechanism.

Statistics of natural scenes and cortical color processing.

PubMed

Cecchi, Guillermo A; Rao, A Ravishankar; Xiao, Youping; Kaplan, Ehud

2010-09-01

We investigate the spatial correlations of orientation and color information in natural images. We find that the correlation of orientation information falls off rapidly with increasing distance, while color information is more highly correlated over longer distances. We show that orientation and color information are statistically independent in natural images and that the spatial correlation of jointly encoded orientation and color information decays faster than that of color alone. Our findings suggest that: (a) orientation and color information should be processed in separate channels and (b) the organization of cortical color and orientation selectivity at low spatial frequencies is a reflection of the cortical adaptation to the statistical structure of the visual world. These findings are in agreement with biological observations, as form and color are thought to be represented by different classes of neurons in the primary visual cortex, and the receptive fields of color-selective neurons are larger than those of orientation-selective neurons. The agreement between our findings and biological observations supports the ecological theory of perception.

PAPR-Constrained Pareto-Optimal Waveform Design for OFDM-STAP Radar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sen, Satyabrata

We propose a peak-to-average power ratio (PAPR) constrained Pareto-optimal waveform design approach for an orthogonal frequency division multiplexing (OFDM) radar signal to detect a target using the space-time adaptive processing (STAP) technique. The use of an OFDM signal does not only increase the frequency diversity of our system, but also enables us to adaptively design the OFDM coefficients in order to further improve the system performance. First, we develop a parametric OFDM-STAP measurement model by considering the effects of signaldependent clutter and colored noise. Then, we observe that the resulting STAP-performance can be improved by maximizing the output signal-to-interference-plus-noise ratiomore » (SINR) with respect to the signal parameters. However, in practical scenarios, the computation of output SINR depends on the estimated values of the spatial and temporal frequencies and target scattering responses. Therefore, we formulate a PAPR-constrained multi-objective optimization (MOO) problem to design the OFDM spectral parameters by simultaneously optimizing four objective functions: maximizing the output SINR, minimizing two separate Cramer-Rao bounds (CRBs) on the normalized spatial and temporal frequencies, and minimizing the trace of CRB matrix on the target scattering coefficients estimations. We present several numerical examples to demonstrate the achieved performance improvement due to the adaptive waveform design.« less

Biologically Inspired Model for Inference of 3D Shape from Texture

PubMed Central

Gomez, Olman; Neumann, Heiko

2016-01-01

A biologically inspired model architecture for inferring 3D shape from texture is proposed. The model is hierarchically organized into modules roughly corresponding to visual cortical areas in the ventral stream. Initial orientation selective filtering decomposes the input into low-level orientation and spatial frequency representations. Grouping of spatially anisotropic orientation responses builds sketch-like representations of surface shape. Gradients in orientation fields and subsequent integration infers local surface geometry and globally consistent 3D depth. From the distributions in orientation responses summed in frequency, an estimate of the tilt and slant of the local surface can be obtained. The model suggests how 3D shape can be inferred from texture patterns and their image appearance in a hierarchically organized processing cascade along the cortical ventral stream. The proposed model integrates oriented texture gradient information that is encoded in distributed maps of orientation-frequency representations. The texture energy gradient information is defined by changes in the grouped summed normalized orientation-frequency response activity extracted from the textured object image. This activity is integrated by directed fields to generate a 3D shape representation of a complex object with depth ordering proportional to the fields output, with higher activity denoting larger distance in relative depth away from the viewer. PMID:27649387

Power spectrum model of visual masking: simulations and empirical data.

PubMed

Serrano-Pedraza, Ignacio; Sierra-Vázquez, Vicente; Derrington, Andrew M

2013-06-01

In the study of the spatial characteristics of the visual channels, the power spectrum model of visual masking is one of the most widely used. When the task is to detect a signal masked by visual noise, this classical model assumes that the signal and the noise are previously processed by a bank of linear channels and that the power of the signal at threshold is proportional to the power of the noise passing through the visual channel that mediates detection. The model also assumes that this visual channel will have the highest ratio of signal power to noise power at its output. According to this, there are masking conditions where the highest signal-to-noise ratio (SNR) occurs in a channel centered in a spatial frequency different from the spatial frequency of the signal (off-frequency looking). Under these conditions the channel mediating detection could vary with the type of noise used in the masking experiment and this could affect the estimation of the shape and the bandwidth of the visual channels. It is generally believed that notched noise, white noise and double bandpass noise prevent off-frequency looking, and high-pass, low-pass and bandpass noises can promote it independently of the channel's shape. In this study, by means of a procedure that finds the channel that maximizes the SNR at its output, we performed numerical simulations using the power spectrum model to study the characteristics of masking caused by six types of one-dimensional noise (white, high-pass, low-pass, bandpass, notched, and double bandpass) for two types of channel's shape (symmetric and asymmetric). Our simulations confirm that (1) high-pass, low-pass, and bandpass noises do not prevent the off-frequency looking, (2) white noise satisfactorily prevents the off-frequency looking independently of the shape and bandwidth of the visual channel, and interestingly we proved for the first time that (3) notched and double bandpass noises prevent off-frequency looking only when the noise cutoffs around the spatial frequency of the signal match the shape of the visual channel (symmetric or asymmetric) involved in the detection. In order to test the explanatory power of the model with empirical data, we performed six visual masking experiments. We show that this model, with only two free parameters, fits the empirical masking data with high precision. Finally, we provide equations of the power spectrum model for six masking noises used in the simulations and in the experiments.

Steady-state VEP responses to uncomfortable stimuli.

PubMed

O'Hare, Louise

2017-02-01

Periodic stimuli, such as op-art, can evoke a range of aversive sensations included in the term visual discomfort. Illusory motion effects are elicited by fixational eye movements, but the cortex might also contribute to effects of discomfort. To investigate this possibility, steady-state visually evoked responses (SSVEPs) to contrast-matched op-art-based stimuli were measured at the same time as discomfort judgements. On average, discomfort reduced with increasing spatial frequency of the pattern. In contrast, the peak amplitude of the SSVEP response was around the midrange spatial frequencies. Like the discomfort judgements, SSVEP responses to the highest spatial frequencies were lowest amplitude, but the relationship breaks down between discomfort and SSVEP for the lower spatial frequency stimuli. This was not explicable by gross eye movements as measured using the facial electrodes. There was a weak relationship between the peak SSVEP responses and discomfort judgements for some stimuli, suggesting that discomfort can be explained in part by electrophysiological responses measured at the level of the cortex. However, there is a breakdown of this relationship in the case of lower spatial frequency stimuli, which remains unexplained. © 2016 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Visual Evoked Cortical Potential (VECP) Elicited by Sinusoidal Gratings Controlled by Pseudo-Random Stimulation

PubMed Central

Araújo, Carolina S.; Souza, Givago S.; Gomes, Bruno D.; Silveira, Luiz Carlos L.

2013-01-01

The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECPs. Single stimulation with spatial contrast temporally controlled by m-sequences has not been extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by pseudo random binary m-sequence at seven spatial frequencies (0.4–10 cpd) and three stimulus sizes (4°, 8°, and 16° of visual angle). At 8° subtence, six contrast levels were used (3.12–99%). The first order kernel (K1) did not provide a consistent measurable signal across spatial frequencies and contrasts that were tested–signal was very small or absent–while the second order kernel first (K2.1) and second (K2.2) slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the K2.1 and K2.2 were in the contrast gain as measured in the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that K2.1 was dominated by M-pathway, but for some stimulus condition some P-pathway contribution could be found, while the second slice reflected the P-pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudorandom stimulation for a wider range of spatial frequencies. PMID:23940546

Modification of response functions of cat visual cortical cells by spatially congruent perturbing stimuli.

PubMed

Kabara, J F; Bonds, A B

2001-12-01

Responses of cat striate cortical cells to a drifting sinusoidal grating were modified by the superimposition of a second, perturbing grating (PG) that did not excite the cell when presented alone. One consequence of the presence of a PG was a shift in the tuning curves. The orientation tuning of all 41 cells exposed to a PG and the spatial frequency tuning of 83% of the 23 cells exposed to a PG showed statistically significant dislocations of both the response function peak and center of mass from their single grating values. As found in earlier reports, the presence of PGs suppressed responsiveness. However, reductions measured at the single grating optimum orientation or spatial frequency were on average 1.3 times greater than the suppression found at the peak of the response function modified by the presence of the PG. Much of the loss in response seen at the single grating optimum is thus a result of a shift in the tuning function rather than outright suppression. On average orientation shifts were repulsive and proportional (approximately 0.10 deg/deg) to the angle between the perturbing stimulus and the optimum single grating orientation. Shifts in the spatial frequency response function were both attractive and repulsive, resulting in an overall average of zero. For both simple and complex cells, PGs generally broadened orientation response function bandwidths. Similarly, complex cell spatial frequency response function bandwidths broadened. Simple cell spatial frequency response functions usually did not change, and those that did broadened only 4% on average. These data support the hypothesis that additional sinusoidal components in compound stimuli retune cells' response functions for orientation and spatial frequency.

Active optics - The NTT and the future

NASA Astrophysics Data System (ADS)

Wilson, R. N.; Franza, F.; Giordano, P.; Noethe, L.; Tarenghi, M.

1988-09-01

An account is given of the essential design features and advantages of the ESO's NTT system optics, constituting an active telescope in which the optical correction process exhibited in histograms can be performed at will, on-line, so that the intrinsic quality of the telescope can be fully realized. This technology allows the relaxation of low spatial frequency (long-wave) manufacturing tolerances, and accomplishes automatic maintenance with respect to errors due to optics' maladjustment. Linearity, convergence, and orthogonality laws are used by the optical correction process algorithm.

Contextual Interactions in Grating Plaid Configurations Are Explained by Natural Image Statistics and Neural Modeling

PubMed Central

Ernst, Udo A.; Schiffer, Alina; Persike, Malte; Meinhardt, Günter

2016-01-01

Processing natural scenes requires the visual system to integrate local features into global object descriptions. To achieve coherent representations, the human brain uses statistical dependencies to guide weighting of local feature conjunctions. Pairwise interactions among feature detectors in early visual areas may form the early substrate of these local feature bindings. To investigate local interaction structures in visual cortex, we combined psychophysical experiments with computational modeling and natural scene analysis. We first measured contrast thresholds for 2 × 2 grating patch arrangements (plaids), which differed in spatial frequency composition (low, high, or mixed), number of grating patch co-alignments (0, 1, or 2), and inter-patch distances (1° and 2° of visual angle). Contrast thresholds for the different configurations were compared to the prediction of probability summation (PS) among detector families tuned to the four retinal positions. For 1° distance the thresholds for all configurations were larger than predicted by PS, indicating inhibitory interactions. For 2° distance, thresholds were significantly lower compared to PS when the plaids were homogeneous in spatial frequency and orientation, but not when spatial frequencies were mixed or there was at least one misalignment. Next, we constructed a neural population model with horizontal laminar structure, which reproduced the detection thresholds after adaptation of connection weights. Consistent with prior work, contextual interactions were medium-range inhibition and long-range, orientation-specific excitation. However, inclusion of orientation-specific, inhibitory interactions between populations with different spatial frequency preferences were crucial for explaining detection thresholds. Finally, for all plaid configurations we computed their likelihood of occurrence in natural images. The likelihoods turned out to be inversely related to the detection thresholds obtained at larger inter-patch distances. However, likelihoods were almost independent of inter-patch distance, implying that natural image statistics could not explain the crowding-like results at short distances. This failure of natural image statistics to resolve the patch distance modulation of plaid visibility remains a challenge to the approach. PMID:27757076

Analysis of Spatial Distribution And Statistical Characteristics of Typhoon In The Western Pacific Based On Spatial Point Model

NASA Astrophysics Data System (ADS)

Wang, Jingmei; Gong, Adu; Li, Jing; Chen, Yanling

2017-04-01

Typhoon is a kind of strong weather system formed in tropical or subtropical oceans. China, located on the west side of the Pacific Ocean, is the country affected by the typhoon most frequently and seriously. To provide theoretical support for effectively reducing the damage caused by typhoon, the variation law of typhoon frequency is explored by analyzing the distribution of typhoon path and landing sites, sphere of influence, and the statistical characteristics of typhoon for every 5 years. In this study, the typhoon point data set was formed using the Best Path Data Set (0.1 ° × 0.1 °) compiled by China Meteorological Administration from 1950 to 2014. By using the tool of Point to Line in software ArgGIS, the typhoon paths are produced from the point data set. The influence sphere of typhoon is calculated from Euclidean distance of typhoon, whose threshold is set to 1°.The typhoon landing site was extracted by using the Chinese vector layer provided by the research group. By counting the frequency of typhoons, the landing sites, and the sphere of influence, some conclusions can be drawn as follows. In recent years, the number of typhoons generated has been reduced, typhoon intensity is relatively stable, but the impact of typhoon area has increased. Specific performance can be seen from the typhoon statistical and spatial distribution characteristics in China. In terms of frequency of typhoon landing, the number of typhoons landing in China has increased while the total number of typhoons is reduced. In terms of distribution of landing sites, the range of typhoon landing fluctuates. However, during the process of fluctuation, the range is gradually expanding. For example, in south of China, Hainan Island is affected by typhoon more frequently meanwhile China's northeast region is also gradually affected, which is extremely unusual before. Key words: spatial point model, distribution of typhoon, frequency of typhoon

Frequency correction method for improved spatial correlation of hyperpolarized 13C metabolites and anatomy.

PubMed

Cunningham, Charles H; Dominguez Viqueira, William; Hurd, Ralph E; Chen, Albert P

2014-02-01

Blip-reversed echo-planar imaging (EPI) is investigated as a method for measuring and correcting the spatial shifts that occur due to bulk frequency offsets in (13)C metabolic imaging in vivo. By reversing the k-space trajectory for every other time point, the direction of the spatial shift for a given frequency is reversed. Here, mutual information is used to find the 'best' alignment between images and thereby measure the frequency offset. Time-resolved 3D images of pyruvate/lactate/urea were acquired with 5 s temporal resolution over a 1 min duration in rats (N = 6). For each rat, a second injection was performed with the demodulation frequency purposely mis-set by +35 Hz, to test the correction for erroneous shifts in the images. Overall, the shift induced by the 35 Hz frequency offset was 5.9 ± 0.6 mm (mean ± standard deviation). This agrees well with the expected 5.7 mm shift based on the 2.02 ms delay between k-space lines (giving 30.9 Hz per pixel). The 0.6 mm standard deviation in the correction corresponds to a frequency-detection accuracy of 4 Hz. A method was presented for ensuring the spatial registration between (13)C metabolic images and conventional anatomical images when long echo-planar readouts are used. The frequency correction method was shown to have an accuracy of 4 Hz. Summing the spatially corrected frames gave a signal-to-noise ratio (SNR) improvement factor of 2 or greater, compared with the highest single frame. Copyright © 2013 John Wiley & Sons, Ltd.

Spatial Intensity Duration Frequency Relationships Using Hierarchical Bayesian Analysis for Urban Areas

NASA Astrophysics Data System (ADS)

Rupa, Chandra; Mujumdar, Pradeep

2016-04-01

In urban areas, quantification of extreme precipitation is important in the design of storm water drains and other infrastructure. Intensity Duration Frequency (IDF) relationships are generally used to obtain design return level for a given duration and return period. Due to lack of availability of extreme precipitation data for sufficiently large number of years, estimating the probability of extreme events is difficult. Typically, a single station data is used to obtain the design return levels for various durations and return periods, which are used in the design of urban infrastructure for the entire city. In an urban setting, the spatial variation of precipitation can be high; the precipitation amounts and patterns often vary within short distances of less than 5 km. Therefore it is crucial to study the uncertainties in the spatial variation of return levels for various durations. In this work, the extreme precipitation is modeled spatially using the Bayesian hierarchical analysis and the spatial variation of return levels is studied. The analysis is carried out with Block Maxima approach for defining the extreme precipitation, using Generalized Extreme Value (GEV) distribution for Bangalore city, Karnataka state, India. Daily data for nineteen stations in and around Bangalore city is considered in the study. The analysis is carried out for summer maxima (March - May), monsoon maxima (June - September) and the annual maxima rainfall. In the hierarchical analysis, the statistical model is specified in three layers. The data layer models the block maxima, pooling the extreme precipitation from all the stations. In the process layer, the latent spatial process characterized by geographical and climatological covariates (lat-lon, elevation, mean temperature etc.) which drives the extreme precipitation is modeled and in the prior level, the prior distributions that govern the latent process are modeled. Markov Chain Monte Carlo (MCMC) algorithm (Metropolis Hastings algorithm within a Gibbs sampler) is used to obtain the samples of parameters from the posterior distribution of parameters. The spatial maps of return levels for specified return periods, along with the associated uncertainties, are obtained for the summer, monsoon and annual maxima rainfall. Considering various covariates, the best fit model is selected using Deviance Information Criteria. It is observed that the geographical covariates outweigh the climatological covariates for the monsoon maxima rainfall (latitude and longitude). The best covariates for summer maxima and annual maxima rainfall are mean summer precipitation and mean monsoon precipitation respectively, including elevation for both the cases. The scale invariance theory, which states that statistical properties of a process observed at various scales are governed by the same relationship, is used to disaggregate the daily rainfall to hourly scales. The spatial maps of the scale are obtained for the study area. The spatial maps of IDF relationships thus generated are useful in storm water designs, adequacy analysis and identifying the vulnerable flooding areas.

Decoherence and Collisional Frequency Shifts of Trapped Bosons and Fermions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibble, Kurt; LNE-SYRTE, Observatoire de Paris, 75014 Paris

2009-09-11

We perform exact calculations of collisional frequency shifts for several fermions or bosons using a singlet and triplet basis for pairs of particles. The 'factor of 2 controversy' for bosons becomes clear - the factor is always 2. Decoherence is described by singlet states and they are unaffected by spatially uniform clock fields. Spatial variations are critical, especially for fermions which were previously thought to be immune to collision shifts. The spatial variations lead to decoherence and a novel frequency shift that is not proportional to the partial density of internal states.

Spatial pattern of long-distance symplasmic transport and communication in trees

PubMed Central

Sokołowska, Katarzyna; Brysz, Alicja Maria; Zagórska-Marek, Beata

2013-01-01

Symplasmic short- and long-distance communication may be regulated at different levels of plant body organization. It depends on cell-to-cell transport modulated by plasmodesmata conductivity and frequency but above all on morphogenetic fields that integrate a plant at the supracellular level. Their control of physiological and developmental processes is especially important in trees, where the continuum consists of 3-dimensional systems of: 1) stem cells in cambium, and 2) living parenchyma cells in the secondary conductive tissues. We found that long-distance symplasmic transport in trees is spatially regulated. Uneven distribution of fluorescent tracer in cambial cells along the branches examined illustrates an unknown intrinsic phenomenon that can possibly be important for plant organism integration. Here we illustrate the spatial dynamics of symplasmic transport in cambium, test and exclude the role of callose in its regulation, and discuss the mechanism that could possibly be responsible for the maintenance of this spatial pattern. PMID:23989002

Image Quality Assessment Using the Joint Spatial/Spatial-Frequency Representation

NASA Astrophysics Data System (ADS)

Beghdadi, Azeddine; Iordache, Răzvan

2006-12-01

This paper demonstrates the usefulness of spatial/spatial-frequency representations in image quality assessment by introducing a new image dissimilarity measure based on 2D Wigner-Ville distribution (WVD). The properties of 2D WVD are shortly reviewed, and the important issue of choosing the analytic image is emphasized. The WVD-based measure is shown to be correlated with subjective human evaluation, which is the premise towards an image quality assessor developed on this principle.

Quantitative evaluation of the risk induced by dominant geomorphological processes on different land uses, based on GIS spatial analysis models

NASA Astrophysics Data System (ADS)

Ştefan, Bilaşco; Sanda, Roşca; Ioan, Fodorean; Iuliu, Vescan; Sorin, Filip; Dănuţ, Petrea

2017-12-01

Maramureş Land is mostly characterized by agricultural and forestry land use due to its specific configuration of topography and its specific pedoclimatic conditions. Taking into consideration the trend of the last century from the perspective of land management, a decrease in the surface of agricultural lands to the advantage of built-up and grass lands, as well as an accelerated decrease in the forest cover due to uncontrolled and irrational forest exploitation, has become obvious. The field analysis performed on the territory of Maramureş Land has highlighted a high frequency of two geomorphologic processes — landslides and soil erosion — which have a major negative impact on land use due to their rate of occurrence. The main aim of the present study is the GIS modeling of the two geomorphologic processes, determining a state of vulnerability (the USLE model for soil erosion and a quantitative model based on the morphometric characteristics of the territory, derived from the HG. 447/2003) and their integration in a complex model of cumulated vulnerability identification. The modeling of the risk exposure was performed using a quantitative approach based on models and equations of spatial analysis, which were developed with modeled raster data structures and primary vector data, through a matrix highlighting the correspondence between vulnerability and land use classes. The quantitative analysis of the risk was performed by taking into consideration the exposure classes as modeled databases and the land price as a primary alphanumeric database using spatial analysis techniques for each class by means of the attribute table. The spatial results highlight the territories with a high risk to present geomorphologic processes that have a high degree of occurrence and represent a useful tool in the process of spatial planning.

Quantitative evaluation of the risk induced by dominant geomorphological processes on different land uses, based on GIS spatial analysis models

NASA Astrophysics Data System (ADS)

Ştefan, Bilaşco; Sanda, Roşca; Ioan, Fodorean; Iuliu, Vescan; Sorin, Filip; Dănuţ, Petrea

2018-06-01

Maramureş Land is mostly characterized by agricultural and forestry land use due to its specific configuration of topography and its specific pedoclimatic conditions. Taking into consideration the trend of the last century from the perspective of land management, a decrease in the surface of agricultural lands to the advantage of built-up and grass lands, as well as an accelerated decrease in the forest cover due to uncontrolled and irrational forest exploitation, has become obvious. The field analysis performed on the territory of Maramureş Land has highlighted a high frequency of two geomorphologic processes — landslides and soil erosion — which have a major negative impact on land use due to their rate of occurrence. The main aim of the present study is the GIS modeling of the two geomorphologic processes, determining a state of vulnerability (the USLE model for soil erosion and a quantitative model based on the morphometric characteristics of the territory, derived from the HG. 447/2003) and their integration in a complex model of cumulated vulnerability identification. The modeling of the risk exposure was performed using a quantitative approach based on models and equations of spatial analysis, which were developed with modeled raster data structures and primary vector data, through a matrix highlighting the correspondence between vulnerability and land use classes. The quantitative analysis of the risk was performed by taking into consideration the exposure classes as modeled databases and the land price as a primary alphanumeric database using spatial analysis techniques for each class by means of the attribute table. The spatial results highlight the territories with a high risk to present geomorphologic processes that have a high degree of occurrence and represent a useful tool in the process of spatial planning.

Nonlinear mechanism for the generation of electromagnetic fields in a magnetized plasma by the beatings of waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aburjania, G. D.; Machabeli, G. Z.; Kharshiladze, O. A.

2006-07-15

The modulational instability in a plasma in a strong constant external magnetic field is considered. The plasmon condensate is modulated not by conventional low-frequency ion sound but by the beatings of two high-frequency transverse electromagnetic waves propagating along the magnetic field. The instability reduces the spatial scales of Langmuir turbulence along the external magnetic field and generates electromagnetic fields. It is shown that, for a pump wave with a sufficiently large amplitude, the effect described in the present paper can be a dominant nonlinear process.

Strong spatial variability in trace gas dynamics following experimental drought in a humid tropical forest

Treesearch

Tana Wood; W. L. Silver

2012-01-01

[1] Soil moisture is a key driver of biogeochemical processes in terrestrial ecosystems, strongly affecting carbon (C) and nutrient availability as well as trace gas production and consumption in soils. Models predict increasing drought frequency in tropical forest ecosystems, which could feed back on future climate change directly via effects on trace gasdynamics and...

Contribution of Binaural Masking Release to Improved Speech Intelligibility for different Masker types.

PubMed

Sutojo, Sarinah; van de Par, Steven; Schoenmaker, Esther

2018-06-01

In situations with competing talkers or in the presence of masking noise, speech intelligibility can be improved by spatially separating the target speaker from the interferers. This advantage is generally referred to as spatial release from masking (SRM) and different mechanisms have been suggested to explain it. One proposed mechanism to benefit from spatial cues is the binaural masking release, which is purely stimulus driven. According to this mechanism, the spatial benefit results from differences in the binaural cues of target and masker, which need to appear simultaneously in time and frequency to improve the signal detection. In an alternative proposed mechanism, the differences in the interaural cues improve the segregation of auditory streams, a process, which involves top-down processing rather than being purely stimulus driven. Other than the cues that produce binaural masking release, the interaural cue differences between target and interferer required to improve stream segregation do not have to appear simultaneously in time and frequency. This study is concerned with the contribution of binaural masking release to SRM for three masker types that differ with respect to the amount of energetic masking they exert. Speech intelligibility was measured, employing a stimulus manipulation that inhibits binaural masking release, and analyzed with a metric to account for the number of better-ear glimpses. Results indicate that the contribution of the stimulus-driven binaural masking release plays a minor role while binaural stream segregation and the availability of glimpses in the better ear had a stronger influence on improving the speech intelligibility. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Impact of Primary Spherical Aberration, Spatial Frequency and Stiles Crawford Apodization on Wavefront determined Refractive Error: A Computational Study

PubMed Central

Xu, Renfeng; Bradley, Arthur; Thibos, Larry N.

2013-01-01

Purpose We tested the hypothesis that pupil apodization is the basis for central pupil bias of spherical refractions in eyes with spherical aberration. Methods We employed Fourier computational optics in which we vary spherical aberration levels, pupil size, and pupil apodization (Stiles Crawford Effect) within the pupil function, from which point spread functions and optical transfer functions were computed. Through-focus analysis determined the refractive correction that optimized retinal image quality. Results For a large pupil (7 mm), as spherical aberration levels increase, refractions that optimize the visual Strehl ratio mirror refractions that maximize high spatial frequency modulation in the image and both focus a near paraxial region of the pupil. These refractions are not affected by Stiles Crawford Effect apodization. Refractions that optimize low spatial frequency modulation come close to minimizing wavefront RMS, and vary with level of spherical aberration and Stiles Crawford Effect. In the presence of significant levels of spherical aberration (e.g. C40 = 0.4 µm, 7mm pupil), low spatial frequency refractions can induce −0.7D myopic shift compared to high SF refraction, and refractions that maximize image contrast of a 3 cycle per degree square-wave grating can cause −0.75D myopic drift relative to refractions that maximize image sharpness. Discussion Because of small depth of focus associated with high spatial frequency stimuli, the large change in dioptric power across the pupil caused by spherical aberration limits the effective aperture contributing to the image of high spatial frequencies. Thus, when imaging high spatial frequencies, spherical aberration effectively induces an annular aperture defining that portion of the pupil contributing to a well-focused image. As spherical focus is manipulated during the refraction procedure, the dimensions of the annular aperture change. Image quality is maximized when the inner radius of the induced annulus falls to zero, thus defining a circular near paraxial region of the pupil that determines refraction outcome. PMID:23683093

Target dependence of orientation and direction selectivity of corticocortical projection neurons in the mouse V1

PubMed Central

Matsui, Teppei; Ohki, Kenichi

2013-01-01

Higher order visual areas that receive input from the primary visual cortex (V1) are specialized for the processing of distinct features of visual information. However, it is still incompletely understood how this functional specialization is acquired. Here we used in vivo two photon calcium imaging in the mouse visual cortex to investigate whether this functional distinction exists at as early as the level of projections from V1 to two higher order visual areas, AL and LM. Specifically, we examined whether sharpness of orientation and direction selectivity and optimal spatial and temporal frequency of projection neurons from V1 to higher order visual areas match with that of target areas. We found that the V1 input to higher order visual areas were indeed functionally distinct: AL preferentially received inputs from V1 that were more orientation and direction selective and tuned for lower spatial frequency compared to projection of V1 to LM, consistent with functional differences between AL and LM. The present findings suggest that selective projections from V1 to higher order visual areas initiates parallel processing of sensory information in the visual cortical network. PMID:24068987

Reference frames for spatial frequency in face representation differ in the temporal visual cortex and amygdala.

PubMed

Inagaki, Mikio; Fujita, Ichiro

2011-07-13

Social communication in nonhuman primates and humans is strongly affected by facial information from other individuals. Many cortical and subcortical brain areas are known to be involved in processing facial information. However, how the neural representation of faces differs across different brain areas remains unclear. Here, we demonstrate that the reference frame for spatial frequency (SF) tuning of face-responsive neurons differs in the temporal visual cortex and amygdala in monkeys. Consistent with psychophysical properties for face recognition, temporal cortex neurons were tuned to image-based SFs (cycles/image) and showed viewing distance-invariant representation of face patterns. On the other hand, many amygdala neurons were influenced by retina-based SFs (cycles/degree), a characteristic that is useful for social distance computation. The two brain areas also differed in the luminance contrast sensitivity of face-responsive neurons; amygdala neurons sharply reduced their responses to low luminance contrast images, while temporal cortex neurons maintained the level of their responses. From these results, we conclude that different types of visual processing in the temporal visual cortex and the amygdala contribute to the construction of the neural representations of faces.

The elimination of zero-order diffraction of 10.6 μm infrared digital holography

NASA Astrophysics Data System (ADS)

Liu, Ning; Yang, Chao

2017-05-01

A new method of eliminating the zero-order diffraction in infrared digital holography has been raised in this paper. Usually in the reconstruction of digital holography, the spatial frequency of the infrared thermal imager, such as microbolometer, cannot be compared to the common visible CCD or CMOS devices. The infrared imager suffers the problems of large pixel size and low spatial resolution, which cause the zero-order diffraction a severe influence of the reconstruction process of digital holograms. The zero-order diffraction has very large energy and occupies the central region in the spectrum domain. In this paper, we design a new filtering strategy to overcome this problem. This filtering strategy contains two kinds of filtering process which are the Gaussian low-frequency filter and the high-pass phase averaging filter. With the correct set of the calculating parameters, these filtering strategies can work effectively on the holograms and fully eliminate the zero-order diffraction, as well as the two crossover bars shown in the spectrum domain. Detailed explanation and discussion about the new method have been proposed in this paper, and the experiment results are also demonstrated to prove the performance of this method.

Evaluation and testing of image quality of the Space Solar Extreme Ultraviolet Telescope

NASA Astrophysics Data System (ADS)

Peng, Jilong; Yi, Zhong; Zhou, Shuhong; Yu, Qian; Hou, Yinlong; Wang, Shanshan

2018-01-01

For the space solar extreme ultraviolet telescope, the star point test can not be performed in the x-ray band (19.5nm band) as there is not light source of bright enough. In this paper, the point spread function of the optical system is calculated to evaluate the imaging performance of the telescope system. Combined with the actual processing surface error, such as small grinding head processing and magnetorheological processing, the optical design software Zemax and data analysis software Matlab are used to directly calculate the system point spread function of the space solar extreme ultraviolet telescope. Matlab codes are programmed to generate the required surface error grid data. These surface error data is loaded to the specified surface of the telescope system by using the communication technique of DDE (Dynamic Data Exchange), which is used to connect Zemax and Matlab. As the different processing methods will lead to surface error with different size, distribution and spatial frequency, the impact of imaging is also different. Therefore, the characteristics of the surface error of different machining methods are studied. Combining with its position in the optical system and simulation its influence on the image quality, it is of great significance to reasonably choose the processing technology. Additionally, we have also analyzed the relationship between the surface error and the image quality evaluation. In order to ensure the final processing of the mirror to meet the requirements of the image quality, we should choose one or several methods to evaluate the surface error according to the different spatial frequency characteristics of the surface error.

The spatial resolving power of earth resources satellites: A review

NASA Technical Reports Server (NTRS)

Townshend, J. R. G.

1980-01-01

The significance of spatial resolving power on the utility of current and future Earth resources satellites is critically discussed and the relative merits of different approaches in defining and estimating spatial resolution are outlined. It is shown that choice of a particular measure of spatial resolution depends strongly on the particular needs of the user. Several experiments have simulated the capabilities of future satellite systems by degradation of aircraft images. Surprisingly, many of these indicated that improvements in resolution may lead to a reduction in the classification accuracy of land cover types using computer assisted methods. However, where the frequency of boundary pixels is high, the converse relationship is found. Use of imagery dependent upon visual interpretation is likely to benefit more consistently from higher resolutions. Extraction of information from images will depend upon several other factors apart from spatial resolving power: these include characteristics of the terrain being sensed, the image processing methods that are applied as well as certain sensor characteristics.

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals

PubMed Central

Fukuda, Yoshiaki; Tomita, Yasuo

2016-01-01

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms. PMID:28773314

Spatial Frequency Responses of Anisotropic Refractive Index Gratings Formed in Holographic Polymer Dispersed Liquid Crystals.

PubMed

Fukuda, Yoshiaki; Tomita, Yasuo

2016-03-10

We report on an experimental investigation of spatial frequency responses of anisotropic transmission refractive index gratings formed in holographic polymer dispersed liquid crystals (HPDLCs). We studied two different types of HPDLC materials employing two different monomer systems: one with acrylate monomer capable of radical mediated chain-growth polymerizations and the other with thiol-ene monomer capable of step-growth polymerizations. It was found that the photopolymerization kinetics of the two HPDLC materials could be well explained by the autocatalytic model. We also measured grating-spacing dependences of anisotropic refractive index gratings at a recording wavelength of 532 nm. It was found that the HPDLC material with the thiol-ene monomer gave higher spatial frequency responses than that with the acrylate monomer. Statistical thermodynamic simulation suggested that such a spatial frequency dependence was attributed primarily to a difference in the size of formed liquid crystal droplets due to different photopolymerization mechanisms.

Spatial filtering with photonic crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maigyte, Lina; Staliunas, Kestutis; Institució Catalana de Recerca i Estudis Avançats

2015-03-15

Photonic crystals are well known for their celebrated photonic band-gaps—the forbidden frequency ranges, for which the light waves cannot propagate through the structure. The frequency (or chromatic) band-gaps of photonic crystals can be utilized for frequency filtering. In analogy to the chromatic band-gaps and the frequency filtering, the angular band-gaps and the angular (spatial) filtering are also possible in photonic crystals. In this article, we review the recent advances of the spatial filtering using the photonic crystals in different propagation regimes and for different geometries. We review the most evident configuration of filtering in Bragg regime (with the back-reflection—i.e., inmore » the configuration with band-gaps) as well as in Laue regime (with forward deflection—i.e., in the configuration without band-gaps). We explore the spatial filtering in crystals with different symmetries, including axisymmetric crystals; we discuss the role of chirping, i.e., the dependence of the longitudinal period along the structure. We also review the experimental techniques to fabricate the photonic crystals and numerical techniques to explore the spatial filtering. Finally, we discuss several implementations of such filters for intracavity spatial filtering.« less

Algebraic signal processing theory: 2-D spatial hexagonal lattice.

PubMed

Pünschel, Markus; Rötteler, Martin

2007-06-01

We develop the framework for signal processing on a spatial, or undirected, 2-D hexagonal lattice for both an infinite and a finite array of signal samples. This framework includes the proper notions of z-transform, boundary conditions, filtering or convolution, spectrum, frequency response, and Fourier transform. In the finite case, the Fourier transform is called discrete triangle transform. Like the hexagonal lattice, this transform is nonseparable. The derivation of the framework makes it a natural extension of the algebraic signal processing theory that we recently introduced. Namely, we construct the proper signal models, given by polynomial algebras, bottom-up from a suitable definition of hexagonal space shifts using a procedure provided by the algebraic theory. These signal models, in turn, then provide all the basic signal processing concepts. The framework developed in this paper is related to Mersereau's early work on hexagonal lattices in the same way as the discrete cosine and sine transforms are related to the discrete Fourier transform-a fact that will be made rigorous in this paper.

Impact imaging of aircraft composite structure based on a model-independent spatial-wavenumber filter.

PubMed

Qiu, Lei; Liu, Bin; Yuan, Shenfang; Su, Zhongqing

2016-01-01

The spatial-wavenumber filtering technique is an effective approach to distinguish the propagating direction and wave mode of Lamb wave in spatial-wavenumber domain. Therefore, it has been gradually studied for damage evaluation in recent years. But for on-line impact monitoring in practical application, the main problem is how to realize the spatial-wavenumber filtering of impact signal when the wavenumber of high spatial resolution cannot be measured or the accurate wavenumber curve cannot be modeled. In this paper, a new model-independent spatial-wavenumber filter based impact imaging method is proposed. In this method, a 2D cross-shaped array constructed by two linear piezoelectric (PZT) sensor arrays is used to acquire impact signal on-line. The continuous complex Shannon wavelet transform is adopted to extract the frequency narrowband signals from the frequency wideband impact response signals of the PZT sensors. A model-independent spatial-wavenumber filter is designed based on the spatial-wavenumber filtering technique. Based on the designed filter, a wavenumber searching and best match mechanism is proposed to implement the spatial-wavenumber filtering of the frequency narrowband signals without modeling, which can be used to obtain a wavenumber-time image of the impact relative to a linear PZT sensor array. By using the two wavenumber-time images of the 2D cross-shaped array, the impact direction can be estimated without blind angle. The impact distance relative to the 2D cross-shaped array can be calculated by using the difference of time-of-flight between the frequency narrowband signals of two different central frequencies and the corresponding group velocities. The validations performed on a carbon fiber composite laminate plate and an aircraft composite oil tank show a good impact localization accuracy of the model-independent spatial-wavenumber filter based impact imaging method. Copyright © 2015 Elsevier B.V. All rights reserved.

Systematic study of high-frequency ultrasonic transducer design for laser-scanning photoacoustic ophthalmoscopy

PubMed Central

Ma, Teng; Zhang, Xiangyang; Chiu, Chi Tat; Chen, Ruimin; Kirk Shung, K.; Zhou, Qifa; Jiao, Shuliang

2014-01-01

Abstract. Photoacoustic ophthalmoscopy (PAOM) is a high-resolution in vivo imaging modality that is capable of providing specific optical absorption information for the retina. A high-frequency ultrasonic transducer is one of the key components in PAOM, which is in contact with the eyelid through coupling gel during imaging. The ultrasonic transducer plays a crucial role in determining the image quality affected by parameters such as spatial resolution, signal-to-noise ratio, and field of view. In this paper, we present the results of a systematic study on a high-frequency ultrasonic transducer design for PAOM. The design includes piezoelectric material selection, frequency selection, and the fabrication process. Transducers of various designs were successfully applied for capturing images of biological samples in vivo. The performances of these designs are compared and evaluated. PMID:24441942

Systematic study of high-frequency ultrasonic transducer design for laser-scanning photoacoustic ophthalmoscopy.

PubMed

Ma, Teng; Zhang, Xiangyang; Chiu, Chi Tat; Chen, Ruimin; Kirk Shung, K; Zhou, Qifa; Jiao, Shuliang

2014-01-01

Photoacoustic ophthalmoscopy (PAOM) is a high-resolution in vivo imaging modality that is capable of providing specific optical absorption information for the retina. A high-frequency ultrasonic transducer is one of the key components in PAOM, which is in contact with the eyelid through coupling gel during imaging. The ultrasonic transducer plays a crucial role in determining the image quality affected by parameters such as spatial resolution, signal-to-noise ratio, and field of view. In this paper, we present the results of a systematic study on a high-frequency ultrasonic transducer design for PAOM. The design includes piezoelectric material selection, frequency selection, and the fabrication process. Transducers of various designs were successfully applied for capturing images of biological samples in vivo. The performances of these designs are compared and evaluated.

Double Fourier analysis for Emotion Identification in Voiced Speech

NASA Astrophysics Data System (ADS)

Sierra-Sosa, D.; Bastidas, M.; Ortiz P., D.; Quintero, O. L.

2016-04-01

We propose a novel analysis alternative, based on two Fourier Transforms for emotion recognition from speech. Fourier analysis allows for display and synthesizes different signals, in terms of power spectral density distributions. A spectrogram of the voice signal is obtained performing a short time Fourier Transform with Gaussian windows, this spectrogram portraits frequency related features, such as vocal tract resonances and quasi-periodic excitations during voiced sounds. Emotions induce such characteristics in speech, which become apparent in spectrogram time-frequency distributions. Later, the signal time-frequency representation from spectrogram is considered an image, and processed through a 2-dimensional Fourier Transform in order to perform the spatial Fourier analysis from it. Finally features related with emotions in voiced speech are extracted and presented.

Computational Approaches to Spatial Orientation: From Transfer Functions to Dynamic Bayesian Inference

PubMed Central

MacNeilage, Paul R.; Ganesan, Narayan; Angelaki, Dora E.

2008-01-01

Spatial orientation is the sense of body orientation and self-motion relative to the stationary environment, fundamental to normal waking behavior and control of everyday motor actions including eye movements, postural control, and locomotion. The brain achieves spatial orientation by integrating visual, vestibular, and somatosensory signals. Over the past years, considerable progress has been made toward understanding how these signals are processed by the brain using multiple computational approaches that include frequency domain analysis, the concept of internal models, observer theory, Bayesian theory, and Kalman filtering. Here we put these approaches in context by examining the specific questions that can be addressed by each technique and some of the scientific insights that have resulted. We conclude with a recent application of particle filtering, a probabilistic simulation technique that aims to generate the most likely state estimates by incorporating internal models of sensor dynamics and physical laws and noise associated with sensory processing as well as prior knowledge or experience. In this framework, priors for low angular velocity and linear acceleration can explain the phenomena of velocity storage and frequency segregation, both of which have been modeled previously using arbitrary low-pass filtering. How Kalman and particle filters may be implemented by the brain is an emerging field. Unlike past neurophysiological research that has aimed to characterize mean responses of single neurons, investigations of dynamic Bayesian inference should attempt to characterize population activities that constitute probabilistic representations of sensory and prior information. PMID:18842952

Quenches across the self-organization transition in multimode cavities

NASA Astrophysics Data System (ADS)

Keller, Tim; Torggler, Valentin; Jäger, Simon B.; Schütz, Stefan; Ritsch, Helmut; Morigi, Giovanna

2018-02-01

A cold dilute atomic gas in an optical resonator can be radiatively cooled by coherent scattering processes when the driving laser frequency is tuned close to but below the cavity resonance. When the atoms are sufficiently illuminated, their steady state undergoes a phase transition from a homogeneous distribution to a spatially organized Bragg grating. We characterize the dynamics of this self-ordering process in the semi-classical regime when distinct cavity modes with commensurate wavelengths are quasi-resonantly driven by laser fields via scattering by the atoms. The lasers are simultaneously applied and uniformly illuminate the atoms; their frequencies are chosen so that the atoms are cooled by the radiative processes, and their intensities are either suddenly switched or slowly ramped across the self-ordering transition. Numerical simulations for different ramp protocols predict that the system will exhibit long-lived metastable states, whose occurrence strongly depends on the initial temperature, ramp speed, and the number of atoms.

Depth Structure from Asymmetric Shading Supports Face Discrimination

PubMed Central

Chen, Chien-Chung; Chen, Chin-Mei; Tyler, Christopher W.

2013-01-01

To examine the effect of illumination direction on the ability of observers to discriminate between faces, we manipulated the direction of illumination on scanned 3D face models. In order to dissociate the surface reflectance and illumination components of front-view face images, we introduce a symmetry algorithm that can separate the symmetric and asymmetric components of the face in both low and high spatial frequency bands. Based on this approach, hybrid faces stimuli were constructed with different combinations of symmetric and asymmetric spatial content. Discrimination results with these images showed that asymmetric illumination information biased face perception toward the structure of the shading component, while the symmetric illumination information had little, if any, effect. Measures of perceived depth showed that this property increased systematically with the asymmetric but not the symmetric low spatial frequency component. Together, these results suggest that (1) the asymmetric 3D shading information dramatically affects both the perceived facial information and the perceived depth of the facial structure; and (2) these effects both increase as the illumination direction is shifted to the side. Thus, our results support the hypothesis that face processing has a strong 3D component. PMID:23457484

Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency

PubMed Central

An, Ran; Massa, Katherine

2014-01-01

AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H+] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H+] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position. PMID:25553200

Detection of fresh bruises in apples by structured-illumination reflectance imaging

NASA Astrophysics Data System (ADS)

Lu, Yuzhen; Li, Richard; Lu, Renfu

2016-05-01

Detection of fresh bruises in apples remains a challenging task due to the absence of visual symptoms and significant chemical alterations of fruit tissues during the initial stage after the fruit have been bruised. This paper reports on a new structured-illumination reflectance imaging (SIRI) technique for enhanced detection of fresh bruises in apples. Using a digital light projector engine, sinusoidally-modulated illumination at the spatial frequencies of 50, 100, 150 and 200 cycles/m was generated. A digital camera was then used to capture the reflectance images from `Gala' and `Jonagold' apples, immediately after they had been subjected to two levels of bruising by impact tests. A conventional three-phase demodulation (TPD) scheme was applied to the acquired images for obtaining the planar (direct component or DC) and amplitude (alternating component or AC) images. Bruises were identified in the amplitude images with varying image contrasts, depending on spatial frequency. The bruise visibility was further enhanced through post-processing of the amplitude images. Furthermore, three spiral phase transform (SPT)-based demodulation methods, using single and two images and two phase-shifted images, were proposed for obtaining AC images. Results showed that the demodulation methods greatly enhanced the contrast and spatial resolution of the AC images, making it feasible to detect the fresh bruises that, otherwise, could not be achieved by conventional imaging technique with planar or uniform illumination. The effectiveness of image enhancement, however, varied with spatial frequency. Both 2-image and 2-phase SPT methods achieved the performance similar to that by conventional TPD. SIRI technique has demonstrated the capability of detecting fresh bruises in apples, and it has the potential as a new imaging modality for enhancing food quality and safety detection.

Anti-aliasing Wiener filtering for wave-front reconstruction in the spatial-frequency domain for high-order astronomical adaptive-optics systems.

PubMed

Correia, Carlos M; Teixeira, Joel

2014-12-01

Computationally efficient wave-front reconstruction techniques for astronomical adaptive-optics (AO) systems have seen great development in the past decade. Algorithms developed in the spatial-frequency (Fourier) domain have gathered much attention, especially for high-contrast imaging systems. In this paper we present the Wiener filter (resulting in the maximization of the Strehl ratio) and further develop formulae for the anti-aliasing (AA) Wiener filter that optimally takes into account high-order wave-front terms folded in-band during the sensing (i.e., discrete sampling) process. We employ a continuous spatial-frequency representation for the forward measurement operators and derive the Wiener filter when aliasing is explicitly taken into account. We further investigate and compare to classical estimates using least-squares filters the reconstructed wave-front, measurement noise, and aliasing propagation coefficients as a function of the system order. Regarding high-contrast systems, we provide achievable performance results as a function of an ensemble of forward models for the Shack-Hartmann wave-front sensor (using sparse and nonsparse representations) and compute point-spread-function raw intensities. We find that for a 32×32 single-conjugated AOs system the aliasing propagation coefficient is roughly 60% of the least-squares filters, whereas the noise propagation is around 80%. Contrast improvements of factors of up to 2 are achievable across the field in the H band. For current and next-generation high-contrast imagers, despite better aliasing mitigation, AA Wiener filtering cannot be used as a standalone method and must therefore be used in combination with optical spatial filters deployed before image formation actually takes place.

Effects of spatial frequency content on classification of face gender and expression.

PubMed

Aguado, Luis; Serrano-Pedraza, Ignacio; Rodríguez, Sonia; Román, Francisco J

2010-11-01

The role of different spatial frequency bands on face gender and expression categorization was studied in three experiments. Accuracy and reaction time were measured for unfiltered, low-pass (cut-off frequency of 1 cycle/deg) and high-pass (cutoff frequency of 3 cycles/deg) filtered faces. Filtered and unfiltered faces were equated in root-mean-squared contrast. For low-pass filtered faces reaction times were higher than unfiltered and high-pass filtered faces in both categorization tasks. In the expression task, these results were obtained with expressive faces presented in isolation (Experiment 1) and also with neutral-expressive dynamic sequences where each expressive face was preceded by a briefly presented neutral version of the same face (Experiment 2). For high-pass filtered faces different effects were observed on gender and expression categorization. While both speed and accuracy of gender categorization were reduced comparing to unfiltered faces, the efficiency of expression classification remained similar. Finally, we found no differences between expressive and non expressive faces in the effects of spatial frequency filtering on gender categorization (Experiment 3). These results show a common role of information from the high spatial frequency band in the categorization of face gender and expression.

The θ-γ neural code.

PubMed

Lisman, John E; Jensen, Ole

2013-03-20

Theta and gamma frequency oscillations occur in the same brain regions and interact with each other, a process called cross-frequency coupling. Here, we review evidence for the following hypothesis: that the dual oscillations form a code for representing multiple items in an ordered way. This form of coding has been most clearly demonstrated in the hippocampus, where different spatial information is represented in different gamma subcycles of a theta cycle. Other experiments have tested the functional importance of oscillations and their coupling. These involve correlation of oscillatory properties with memory states, correlation with memory performance, and effects of disrupting oscillations on memory. Recent work suggests that this coding scheme coordinates communication between brain regions and is involved in sensory as well as memory processes. Copyright © 2013 Elsevier Inc. All rights reserved.

Mutual Information in Frequency and Its Application to Measure Cross-Frequency Coupling in Epilepsy

NASA Astrophysics Data System (ADS)

Malladi, Rakesh; Johnson, Don H.; Kalamangalam, Giridhar P.; Tandon, Nitin; Aazhang, Behnaam

2018-06-01

We define a metric, mutual information in frequency (MI-in-frequency), to detect and quantify the statistical dependence between different frequency components in the data, referred to as cross-frequency coupling and apply it to electrophysiological recordings from the brain to infer cross-frequency coupling. The current metrics used to quantify the cross-frequency coupling in neuroscience cannot detect if two frequency components in non-Gaussian brain recordings are statistically independent or not. Our MI-in-frequency metric, based on Shannon's mutual information between the Cramer's representation of stochastic processes, overcomes this shortcoming and can detect statistical dependence in frequency between non-Gaussian signals. We then describe two data-driven estimators of MI-in-frequency: one based on kernel density estimation and the other based on the nearest neighbor algorithm and validate their performance on simulated data. We then use MI-in-frequency to estimate mutual information between two data streams that are dependent across time, without making any parametric model assumptions. Finally, we use the MI-in- frequency metric to investigate the cross-frequency coupling in seizure onset zone from electrocorticographic recordings during seizures. The inferred cross-frequency coupling characteristics are essential to optimize the spatial and spectral parameters of electrical stimulation based treatments of epilepsy.

Context processing in adolescents with autism spectrum disorder: How complex could it be?

PubMed

Ben-Yosef, Dekel; Anaki, David; Golan, Ofer

2017-03-01

The ability of individuals with Autism Spectrum Disorder (ASD) to process context has long been debated: According to the Weak Central Coherence theory, ASD is characterized by poor global processing, and consequently-poor context processing. In contrast, the Social Cognition theory argues individuals with ASD will present difficulties only in social context processing. The complexity theory of autism suggests context processing in ASD will depend on task complexity. The current study examined this controversy through two priming tasks, one presenting human stimuli (facial expressions) and the other presenting non-human stimuli (animal faces). Both tasks presented visual targets, preceded by congruent, incongruent, or neutral auditory primes. Local and global processing were examined by presenting the visual targets in three spatial frequency conditions: High frequency, low frequency, and broadband. Tasks were administered to 16 adolescents with high functioning ASD and 16 matched typically developing adolescents. Reaction time and accuracy were measured for each task in each condition. Results indicated that individuals with ASD processed context for both human and non-human stimuli, except in one condition, in which human stimuli had to be processed globally (i.e., target presented in low frequency). The task demands presented in this condition, and the performance deficit shown in the ASD group as a result, could be understood in terms of cognitive overload. These findings provide support for the complexity theory of autism and extend it. Our results also demonstrate how associative priming could support intact context processing of human and non-human stimuli in individuals with ASD. Autism Res 2017, 10: 520-530. © 2016 International Society for Autism Research, Wiley Periodicals, Inc. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Ladar imaging detection of salient map based on PWVD and Rényi entropy

NASA Astrophysics Data System (ADS)

Xu, Yuannan; Zhao, Yuan; Deng, Rong; Dong, Yanbing

2013-10-01

Spatial-frequency information of a given image can be extracted by associating the grey-level spatial data with one of the well-known spatial/spatial-frequency distributions. The Wigner-Ville distribution (WVD) has a good characteristic that the images can be represented in spatial/spatial-frequency domains. For intensity and range images of ladar, through the pseudo Wigner-Ville distribution (PWVD) using one or two dimension window, the statistical property of Rényi entropy is studied. We also analyzed the change of Rényi entropy's statistical property in the ladar intensity and range images when the man-made objects appear. From this foundation, a novel method for generating saliency map based on PWVD and Rényi entropy is proposed. After that, target detection is completed when the saliency map is segmented using a simple and convenient threshold method. For the ladar intensity and range images, experimental results show the proposed method can effectively detect the military vehicles from complex earth background with low false alarm.

Temporal and spatial tuning of dorsal lateral geniculate nucleus neurons in unanesthetized rats

PubMed Central

Sriram, Balaji; Meier, Philip M.

2016-01-01

Visual response properties of neurons in the dorsolateral geniculate nucleus (dLGN) have been well described in several species, but not in rats. Analysis of responses from the unanesthetized rat dLGN will be needed to develop quantitative models that account for visual behavior of rats. We recorded visual responses from 130 single units in the dLGN of 7 unanesthetized rats. We report the response amplitudes, temporal frequency, and spatial frequency sensitivities in this population of cells. In response to 2-Hz visual stimulation, dLGN cells fired 15.9 ± 11.4 spikes/s (mean ± SD) modulated by 10.7 ± 8.4 spikes/s about the mean. The optimal temporal frequency for full-field stimulation ranged from 5.8 to 19.6 Hz across cells. The temporal high-frequency cutoff ranged from 11.7 to 33.6 Hz. Some cells responded best to low temporal frequency stimulation (low pass), and others were strictly bandpass; most cells fell between these extremes. At 2- to 4-Hz temporal modulation, the spatial frequency of drifting grating that drove cells best ranged from 0.008 to 0.18 cycles per degree (cpd) across cells. The high-frequency cutoff ranged from 0.01 to 1.07 cpd across cells. The majority of cells were driven best by the lowest spatial frequency tested, but many were partially or strictly bandpass. We conclude that single units in the rat dLGN can respond vigorously to temporal modulation up to at least 30 Hz and spatial detail up to 1 cpd. Tuning properties were heterogeneous, but each fell along a continuum; we found no obvious clustering into discrete cell types along these dimensions. PMID:26936980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novak, Erik; Trolinger, James D.; Lacey, Ian

This work reports on the development of a binary pseudo-random test sample optimized to calibrate the MTF of optical microscopes. The sample consists of a number of 1-D and 2-D patterns, with different minimum sizes of spatial artifacts from 300 nm to 2 microns. We describe the mathematical background, fabrication process, data acquisition and analysis procedure to return spatial frequency based instrument calibration. We show that the developed samples satisfy the characteristics of a test standard: functionality, ease of specification and fabrication, reproducibility, and low sensitivity to manufacturing error. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading ofmore » the abstract is permitted for personal use only.« less

Final Technical Report for DE-SC0008149

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buchanan, Kristen

The major goal of this project is to study spin waves in magnetic thin films, especially how spin waves respond to external stimuli. This is expected to lead to new insight into dynamic processes and new ideas for methods to control spin waves. Experimental studies are being done primarily using time- and spatially-resolved Brillouin light scattering (BLS) measurements on extended and patterned magnetic thin films. BLS is a versatile tool that provides a non-invasive probe of spin dynamics with frequencies of ~1 GHz to well over 100 GHz, diffraction-limited spatial resolution, 250-ps temporal resolution, and it is sensitive enough tomore » detect thermal magnons.« less

Relative saliency in change signals affects perceptual comparison and decision processes in change detection.

PubMed

Yang, Cheng-Ta

2011-12-01

Change detection requires perceptual comparison and decision processes on different features of multiattribute objects. How relative salience between two feature-changes influences the processes has not been addressed. This study used the systems factorial technology to investigate the processes when detecting changes in a Gabor patch with visual inputs from orientation and spatial frequency channels. Two feature-changes were equally salient in Experiment 1, but a frequency-change was more salient than an orientation-change in Experiment 2. Results showed that all four observers adopted parallel self-terminating processing with limited- to unlimited-capacity processing in Experiment 1. In Experiment 2, one observer used parallel self-terminating processing with unlimited-capacity processing, and the others adopted serial self-terminating processing with limited- to unlimited-capacity processing to detect changes. Postexperimental interview revealed that subjective utility of feature information underlay the adoption of a decision strategy. These results highlight that observers alter decision strategies in change detection depending on the relative saliency in change signals, with relative saliency being determined by both physical salience and subjective weight of feature information. When relative salience exists, individual differences in the process characteristics emerge.

Growth Twinning and Generation of High-Frequency Surface Nanostructures in Ultrafast Laser-Induced Transient Melting and Resolidification.

PubMed

Sedao, Xxx; Shugaev, Maxim V; Wu, Chengping; Douillard, Thierry; Esnouf, Claude; Maurice, Claire; Reynaud, Stéphanie; Pigeon, Florent; Garrelie, Florence; Zhigilei, Leonid V; Colombier, Jean-Philippe

2016-07-26

The structural changes generated in surface regions of single crystal Ni targets by femtosecond laser irradiation are investigated experimentally and computationally for laser fluences that, in the multipulse irradiation regime, produce sub-100 nm high spatial frequency surface structures. Detailed experimental characterization of the irradiated targets combining electron back scattered diffraction analysis with high-resolution transmission electron microscopy reveals the presence of multiple nanoscale twinned domains in the irradiated surface regions of single crystal targets with (111) surface orientation. Atomistic- and continuum-level simulations performed for experimental irradiation conditions reproduce the generation of twinned domains and establish the conditions leading to the formation of growth twin boundaries in the course of the fast transient melting and epitaxial regrowth of the surface regions of the irradiated targets. The observation of growth twins in the irradiated Ni(111) targets provides strong evidence of the role of surface melting and resolidification in the formation of high spatial frequency surface structures. This also suggests that the formation of twinned domains can be used as a sensitive measure of the levels of liquid undercooling achieved in short pulse laser processing of metals.

High Speed Computational Ghost Imaging via Spatial Sweeping

NASA Astrophysics Data System (ADS)

Wang, Yuwang; Liu, Yang; Suo, Jinli; Situ, Guohai; Qiao, Chang; Dai, Qionghai

2017-03-01

Computational ghost imaging (CGI) achieves single-pixel imaging by using a Spatial Light Modulator (SLM) to generate structured illuminations for spatially resolved information encoding. The imaging speed of CGI is limited by the modulation frequency of available SLMs, and sets back its practical applications. This paper proposes to bypass this limitation by trading off SLM’s redundant spatial resolution for multiplication of the modulation frequency. Specifically, a pair of galvanic mirrors sweeping across the high resolution SLM multiply the modulation frequency within the spatial resolution gap between SLM and the final reconstruction. A proof-of-principle setup with two middle end galvanic mirrors achieves ghost imaging as fast as 42 Hz at 80 × 80-pixel resolution, 5 times faster than state-of-the-arts, and holds potential for one magnitude further multiplication by hardware upgrading. Our approach brings a significant improvement in the imaging speed of ghost imaging and pushes ghost imaging towards practical applications.

Large-Scale Multiantenna Multisine Wireless Power Transfer

NASA Astrophysics Data System (ADS)

Huang, Yang; Clerckx, Bruno

2017-11-01

Wireless Power Transfer (WPT) is expected to be a technology reshaping the landscape of low-power applications such as the Internet of Things, Radio Frequency identification (RFID) networks, etc. Although there has been some progress towards multi-antenna multi-sine WPT design, the large-scale design of WPT, reminiscent of massive MIMO in communications, remains an open challenge. In this paper, we derive efficient multiuser algorithms based on a generalizable optimization framework, in order to design transmit sinewaves that maximize the weighted-sum/minimum rectenna output DC voltage. The study highlights the significant effect of the nonlinearity introduced by the rectification process on the design of waveforms in multiuser systems. Interestingly, in the single-user case, the optimal spatial domain beamforming, obtained prior to the frequency domain power allocation optimization, turns out to be Maximum Ratio Transmission (MRT). In contrast, in the general weighted sum criterion maximization problem, the spatial domain beamforming optimization and the frequency domain power allocation optimization are coupled. Assuming channel hardening, low-complexity algorithms are proposed based on asymptotic analysis, to maximize the two criteria. The structure of the asymptotically optimal spatial domain precoder can be found prior to the optimization. The performance of the proposed algorithms is evaluated. Numerical results confirm the inefficiency of the linear model-based design for the single and multi-user scenarios. It is also shown that as nonlinear model-based designs, the proposed algorithms can benefit from an increasing number of sinewaves.

Fault detection in rotating machines with beamforming: Spatial visualization of diagnosis features

NASA Astrophysics Data System (ADS)

Cardenas Cabada, E.; Leclere, Q.; Antoni, J.; Hamzaoui, N.

2017-12-01

Rotating machines diagnosis is conventionally related to vibration analysis. Sensors are usually placed on the machine to gather information about its components. The recorded signals are then processed through a fault detection algorithm allowing the identification of the failing part. This paper proposes an acoustic-based diagnosis method. A microphone array is used to record the acoustic field radiated by the machine. The main advantage over vibration-based diagnosis is that the contact between the sensors and the machine is no longer required. Moreover, the application of acoustic imaging makes possible the identification of the sources of acoustic radiation on the machine surface. The display of information is then spatially continuous while the accelerometers only give it discrete. Beamforming provides the time-varying signals radiated by the machine as a function of space. Any fault detection tool can be applied to the beamforming output. Spectral kurtosis, which highlights the impulsiveness of a signal as function of frequency, is used in this study. The combination of spectral kurtosis with acoustic imaging makes possible the mapping of the impulsiveness as a function of space and frequency. The efficiency of this approach lays on the source separation in the spatial and frequency domains. These mappings make possible the localization of such impulsive sources. The faulty components of the machine have an impulsive behavior and thus will be highlighted on the mappings. The study presents experimental validations of the method on rotating machines.

Stimulus discriminability in visual search.

PubMed

Verghese, P; Nakayama, K

1994-09-01

We measured the probability of detecting the target in a visual search task, as a function of the following parameters: the discriminability of the target from the distractors, the duration of the display, and the number of elements in the display. We examined the relation between these parameters at criterion performance (80% correct) to determine if the parameters traded off according to the predictions of a limited capacity model. For the three dimensions that we studied, orientation, color, and spatial frequency, the observed relationship between the parameters deviates significantly from a limited capacity model. The data relating discriminability to display duration are better than predicted over the entire range of orientation and color differences that we examined, and are consistent with the prediction for only a limited range of spatial frequency differences--from 12 to 23%. The relation between discriminability and number varies considerably across the three dimensions and is better than the limited capacity prediction for two of the three dimensions that we studied. Orientation discrimination shows a strong number effect, color discrimination shows almost no effect, and spatial frequency discrimination shows an intermediate effect. The different trading relationships in each dimension are more consistent with early filtering in that dimension, than with a common limited capacity stage. Our results indicate that higher-level processes that group elements together also play a strong role. Our experiments provide little support for limited capacity mechanisms over the range of stimulus differences that we examined in three different dimensions.

Conscious and unconscious processing of facial expressions: evidence from two split-brain patients.

PubMed

Prete, Giulia; D'Ascenzo, Stefania; Laeng, Bruno; Fabri, Mara; Foschi, Nicoletta; Tommasi, Luca

2015-03-01

We investigated how the brain's hemispheres process explicit and implicit facial expressions in two 'split-brain' patients (one with a complete and one with a partial anterior resection). Photographs of faces expressing positive, negative or neutral emotions were shown either centrally or bilaterally. The task consisted in judging the friendliness of each person in the photographs. Half of the photograph stimuli were 'hybrid faces', that is an amalgamation of filtered images which contained emotional information only in the low range of spatial frequency, blended to a neutral expression of the same individual in the rest of the spatial frequencies. The other half of the images contained unfiltered faces. With the hybrid faces the patients and a matched control group were more influenced in their social judgements by the emotional expression of the face shown in the left visual field (LVF). When the expressions were shown explicitly, that is without filtering, the control group and the partially callosotomized patient based their judgement on the face shown in the LVF, whereas the complete split-brain patient based his ratings mainly on the face presented in the right visual field. We conclude that the processing of implicit emotions does not require the integrity of callosal fibres and can take place within subcortical routes lateralized in the right hemisphere. © 2013 The British Psychological Society.

Integrated use of spatial and semantic relationships for extracting road networks from floating car data

NASA Astrophysics Data System (ADS)

Li, Jun; Qin, Qiming; Xie, Chao; Zhao, Yue

2012-10-01

The update frequency of digital road maps influences the quality of road-dependent services. However, digital road maps surveyed by probe vehicles or extracted from remotely sensed images still have a long updating circle and their cost remain high. With GPS technology and wireless communication technology maturing and their cost decreasing, floating car technology has been used in traffic monitoring and management, and the dynamic positioning data from floating cars become a new data source for updating road maps. In this paper, we aim to update digital road maps using the floating car data from China's National Commercial Vehicle Monitoring Platform, and present an incremental road network extraction method suitable for the platform's GPS data whose sampling frequency is low and which cover a large area. Based on both spatial and semantic relationships between a trajectory point and its associated road segment, the method classifies each trajectory point, and then merges every trajectory point into the candidate road network through the adding or modifying process according to its type. The road network is gradually updated until all trajectories have been processed. Finally, this method is applied in the updating process of major roads in North China and the experimental results reveal that it can accurately derive geometric information of roads under various scenes. This paper provides a highly-efficient, low-cost approach to update digital road maps.

Probing the Spatio-Temporal Characteristics of Temporal Aliasing Errors and their Impact on Satellite Gravity Retrievals

NASA Astrophysics Data System (ADS)

Wiese, D. N.; McCullough, C. M.

2017-12-01

Studies have shown that both single pair low-low satellite-to-satellite tracking (LL-SST) and dual-pair LL-SST hypothetical future satellite gravimetry missions utilizing improved onboard measurement systems relative to the Gravity Recovery and Climate Experiment (GRACE) will be limited by temporal aliasing errors; that is, the error introduced through deficiencies in models of high frequency mass variations required for the data processing. Here, we probe the spatio-temporal characteristics of temporal aliasing errors to understand their impact on satellite gravity retrievals using high fidelity numerical simulations. We find that while aliasing errors are dominant at long wavelengths and multi-day timescales, improving knowledge of high frequency mass variations at these resolutions translates into only modest improvements (i.e. spatial resolution/accuracy) in the ability to measure temporal gravity variations at monthly timescales. This result highlights the reliance on accurate models of high frequency mass variations for gravity processing, and the difficult nature of reducing temporal aliasing errors and their impact on satellite gravity retrievals.

Population receptive field (pRF) measurements of chromatic responses in human visual cortex using fMRI.

PubMed

Welbourne, Lauren E; Morland, Antony B; Wade, Alex R

2018-02-15

The spatial sensitivity of the human visual system depends on stimulus color: achromatic gratings can be resolved at relatively high spatial frequencies while sensitivity to isoluminant color contrast tends to be more low-pass. Models of early spatial vision often assume that the receptive field size of pattern-sensitive neurons is correlated with their spatial frequency sensitivity - larger receptive fields are typically associated with lower optimal spatial frequency. A strong prediction of this model is that neurons coding isoluminant chromatic patterns should have, on average, a larger receptive field size than neurons sensitive to achromatic patterns. Here, we test this assumption using functional magnetic resonance imaging (fMRI). We show that while spatial frequency sensitivity depends on chromaticity in the manner predicted by behavioral measurements, population receptive field (pRF) size measurements show no such dependency. At any given eccentricity, the mean pRF size for neuronal populations driven by luminance, opponent red/green and S-cone isolating contrast, are identical. Changes in pRF size (for example, an increase with eccentricity and visual area hierarchy) are also identical across the three chromatic conditions. These results suggest that fMRI measurements of receptive field size and spatial resolution can be decoupled under some circumstances - potentially reflecting a fundamental dissociation between these parameters at the level of neuronal populations. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Using fire return interval departure (FRID) analysis to map spatial and temporal changes in fire frequency on national forest lands in California

Treesearch

Hugh D. Safford; Kip M. Van de Water

2014-01-01

In California, fire regimes and related ecosystem processes have been altered by land use practices associated with Euro-American settlement, and climate warming is exacerbating the magnitude and effects of these changes. Because of changing environmental baselines, restoration of narrowly defined historical conditions may no longer be an attainable or sustainable long...

High frequency longitudinal profiling reveals hydrologic controls on solute sourcing, transport and processing in a karst river

NASA Astrophysics Data System (ADS)

Hensley, R. T.; Cohen, M. J.; Spangler, M.; Gooseff, M. N.

2017-12-01

The lower Santa Fe River is a large, karst river of north Florida, fed by numerous artesian springs and also containing multiple sink-rise systems. We performed repeated longitudinal profiles collecting very high frequency measurements of multiple stream parameters including temperature, dissolved oxygen, carbon dioxide, pH, dissolved organic matter, nitrate, ammonium, phosphate and turbidity. This high frequency dataset provided a spatially explicit understanding of solute sources and coupled biogeochemical processing rates along the 25 km study reach. We noted marked changes in river profiles as the river transitioned from low to high flow during the onset of the wet season. The role of lateral inflow from springs as the primary solute source was greatly reduced under high flow conditions. Effects of sink-rise systems, which under low flow conditions allow the majority of flow to bypass several kilometer long sections of the main channel, virtually disappeared under high flow conditions. Impeded light transmittance at high flow reduced primary production and by extension assimilatory nutrient uptake. This study demonstrates how high frequency longitudinal profiling can be used to observe how hydrologic conditions can alter groundwater-surface water interactions and modulate the sourcing, transport and biogeochemical processing of stream solutes.

Electrophysiological spatiotemporal dynamics during implicit visual threat processing.

PubMed

DeLaRosa, Bambi L; Spence, Jeffrey S; Shakal, Scott K M; Motes, Michael A; Calley, Clifford S; Calley, Virginia I; Hart, John; Kraut, Michael A

2014-11-01

Numerous studies have found evidence for corticolimbic theta band electroencephalographic (EEG) oscillations in the neural processing of visual stimuli perceived as threatening. However, varying temporal and topographical patterns have emerged, possibly due to varying arousal levels of the stimuli. In addition, recent studies suggest neural oscillations in delta, theta, alpha, and beta-band frequencies play a functional role in information processing in the brain. This study implemented a data-driven PCA based analysis investigating the spatiotemporal dynamics of electroencephalographic delta, theta, alpha, and beta-band frequencies during an implicit visual threat processing task. While controlling for the arousal dimension (the intensity of emotional activation), we found several spatial and temporal differences for threatening compared to nonthreatening visual images. We detected an early posterior increase in theta power followed by a later frontal increase in theta power, greatest for the threatening condition. There was also a consistent left lateralized beta desynchronization for the threatening condition. Our results provide support for a dynamic corticolimbic network, with theta and beta band activity indexing processes pivotal in visual threat processing. Published by Elsevier Inc.

An analysis of Greek seismicity based on Non Extensive Statistical Physics: The interdependence of magnitude, interevent time and interevent distance.

NASA Astrophysics Data System (ADS)

Efstathiou, Angeliki; Tzanis, Andreas; Vallianatos, Filippos

2014-05-01

The context of Non Extensive Statistical Physics (NESP) has recently been suggested to comprise an appropriate tool for the analysis of complex dynamic systems with scale invariance, long-range interactions, long-range memory and systems that evolve in a fractal-like space-time. This is because the active tectonic grain is thought to comprise a (self-organizing) complex system; therefore, its expression (seismicity) should be manifested in the temporal and spatial statistics of energy release rates. In addition to energy release rates expressed by the magnitude M, measures of the temporal and spatial interactions are the time (Δt) and hypocentral distance (Δd) between consecutive events. Recent work indicated that if the distributions of M, Δt and Δd are independent so that the joint probability p(M,Δt,Δd) factorizes into the probabilities of M, Δt and Δd, i.e. p(M,Δt,Δd)= p(M)p(Δt)p(Δd), then the frequency of earthquake occurrence is multiply related, not only to magnitude as the celebrated Gutenberg - Richter law predicts, but also to interevent time and distance by means of well-defined power-laws consistent with NESP. The present work applies these concepts to investigate the self-organization and temporal/spatial dynamics of seismicity in Greece and western Turkey, for the period 1964-2011. The analysis was based on the ISC earthquake catalogue which is homogenous by construction with consistently determined hypocenters and magnitude. The presentation focuses on the analysis of bivariate Frequency-Magnitude-Time distributions, while using the interevent distances as spatial constraints (or spatial filters) for studying the spatial dependence of the energy and time dynamics of the seismicity. It is demonstrated that the frequency of earthquake occurrence is multiply related to the magnitude and the interevent time by means of well-defined multi-dimensional power-laws consistent with NESP and has attributes of universality,as its holds for a broad range of spatial, temporal and magnitude scales. Provided that the multivariate empirical frequency distributions are based on a sufficient number of observations as an empirical lower limit, the results are stable and consistent with the established ken, irrespective of the magnitude and spatio-temporal range of the earthquake catalogue, or operations pertaining to re-sampling, bootstrapping or re-arrangement of the catalogue. It is also demonstrated that that the expression of the regional active tectonic grain may comprise a mixture of processes significantly dependent on Δd. The analysis of the size (energy) distribution of earthquakes yielded results consistent with a correlated sub-extensive system; the results are also consistent with conventional determinations of Frequency-Magnitude distributions. The analysis of interevent times, has determined the existence of sub-extensivity and near-field interaction (correlation) in the complete catalogue of Greek and western Turkish seismicity (mixed background earthquake activity and aftershock processes),as well as in the pure background process (declustered catalogue).This could be attributed to the joint effect of near-field interaction between neighbouring earthquakes or seismic areas and interaction within aftershock sequences. The background process appears to be moderately - weakly correlated at the far field. Formal random temporal processes have not been detected. A general syllogism affordable by the above observations is that aftershock sequences may be an integral part of the seismogenetic process, as they appear to partake in long-range interaction. A formal explanation of such an effect is pending, but may nevertheless involve delayed remote triggering of seismic activity by (transient or static) stress transfer from the main shocks and large aftershocks and/or cascading effects already discussed by Marsan and Lengliné (2008). In this view, the effect weakens when aftershocks are removed because aftershocks are the link between the main shocks and their remote offshoot. Overall, the above results compare well to the results of North Californian seismicity which have shown that the expression of seismicity at Northern California is generally consistent with non-extensive (sub-extensive) thermodynamics. Acknowledgments: This work was supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project "Integrated understanding of Seismicity, using innovative methodologies of Fracture Mechanics along with Earthquake and Non-Extensive Statistical Physics - Application to the geodynamic system of the Hellenic Arc - SEISMO FEAR HELLARC". References: Tzanis A., Vallianatos F., Efstathiou A., Multidimensional earthquake frequency distributions consistent with Non-Extensive Statistical Physics: the interdependence of magnitude, interevent time and interevent distance in North California. Bulletin of the Geological Society of Greece, vol. XLVII 2013. Proceedings of the 13th International Congress, Chania, Sept. 2013 Tzanis A., Vallianatos F., Efstathiou A., Generalized multidimensional earthquake frequency distributions consistent with Non-Extensive Statistical Physics: An appraisal of the universality in the interdependence of magnitude, interevent time and interevent distance Geophysical Research Abstracts, Vol. 15, EGU2013-628, 2013, EGU General Assembly 2013 Marsan, D. and Lengliné, O., 2008. Extending earthquakes's reach through cascading, Science, 319, 1076; doi: 10.1126/science.1148783 On-line Bulletin, http://www.isc.ac.uk, Internatl. Seis. Cent., Thatcham, United Kingdom, 2011.

[Multi-channel in vivo recording techniques: signal processing of action potentials and local field potentials].

PubMed

Xu, Jia-Min; Wang, Ce-Qun; Lin, Long-Nian

2014-06-25

Multi-channel in vivo recording techniques are used to record ensemble neuronal activity and local field potentials (LFP) simultaneously. One of the key points for the technique is how to process these two sets of recorded neural signals properly so that data accuracy can be assured. We intend to introduce data processing approaches for action potentials and LFP based on the original data collected through multi-channel recording system. Action potential signals are high-frequency signals, hence high sampling rate of 40 kHz is normally chosen for recording. Based on waveforms of extracellularly recorded action potentials, tetrode technology combining principal component analysis can be used to discriminate neuronal spiking signals from differently spatially distributed neurons, in order to obtain accurate single neuron spiking activity. LFPs are low-frequency signals (lower than 300 Hz), hence the sampling rate of 1 kHz is used for LFPs. Digital filtering is required for LFP analysis to isolate different frequency oscillations including theta oscillation (4-12 Hz), which is dominant in active exploration and rapid-eye-movement (REM) sleep, gamma oscillation (30-80 Hz), which is accompanied by theta oscillation during cognitive processing, and high frequency ripple oscillation (100-250 Hz) in awake immobility and slow wave sleep (SWS) state in rodent hippocampus. For the obtained signals, common data post-processing methods include inter-spike interval analysis, spike auto-correlation analysis, spike cross-correlation analysis, power spectral density analysis, and spectrogram analysis.

Space and time scales of shoreline change at Cape Cod National Seashore, MA, USA

USGS Publications Warehouse

Allen, J.R.; LaBash, C.L.; List, J.H.; Kraus, Nicholas C.; McDougal, William G.

1999-01-01

Different processes cause patterns of shoreline change which are exhibited at different magnitudes and nested into different spatial and time scale hierarchies. The 77-km outer beach at Cape Cod National Seashore offers one of the few U.S. federally owned portions of beach to study shoreline change within the full range of sediment source and sink relationships, and barely affected by human intervention. 'Mean trends' of shoreline changes are best observed at long time scales but contain much spatial variation thus many sites are not equal in response. Long-term, earlier-noted trends are confirmed but the added quantification and resolution improves greatly the understanding of appropriate spatial and time scales of those processes driving bluff retreat and barrier island changes in both north and south depocenters. Shorter timescales allow for comparison of trends and uncertainty in shoreline change at local scales but are dependent upon some measure of storm intensity and seasonal frequency. Single-event shoreline survey results for one storm at daily intervals after the erosional phase suggest a recovery time for the system of six days, identifies three sites with abnormally large change, and that responses at these sites are spatially coherent for now unknown reasons. Areas near inlets are the most variable at all time scales. Hierarchies in both process and form are suggested.

Spatially Detailed Porosity Prediction From Airborne Electromagnetics and Sparse Borehole Fluid Sampling

NASA Astrophysics Data System (ADS)

Macnae, J.; Ley-Cooper, Y.

2009-05-01

Sub-surface porosity is of importance in estimating fluid contant and salt-load parameters for hydrological modelling. While sparse boreholes may adequately sample the depth to a sub-horizontal water-table and usually also adequately sample ground-water salinity, they do not provide adequate sampling of the spatial variations in porosity or hydraulic permeability caused by spatial variations in sedimentary and other geological processes.. We show in this presentation that spatially detailed porosity can be estimated by applying Archie's law to conductivity estimates from airborne electromagnetic surveys with interpolated ground-water conductivity values. The prediction was tested on data from the Chowilla flood plain in the Murray-Darling Basin of South Australia. A frequency domain, helicopter-borne electromagnetic system collected data at 6 frequencies and 3 to 4 m spacings on lines spaced 100 m apart. This data was transformed into conductivity-depth sections, from which a 3D bulk-conductivity map could be created with about 30 m spatial resolution and 2 to 5 m vertical depth resolution. For that portion of the volume below the interpolated water-table, we predicted porosity in each cell using Archie's law. Generally, predicted porosities were in the 30 to 50 % range, consistent with expectations for the partially consolidated sediments in the floodplain. Porosities were directly measured on core from eight boreholes in the area, and compared quite well with the predictions. The predicted porosity map was spatially consistent, and when combined with measured salinities in the ground water, was able to provide a detailed 3D map of salt-loads in the saturated zone, and as such contribute to a hazard assessment of the saline threat to the river.

Evaluation of Spatial Pattern of Altered Flow Regimes on a River Network Using a Distributed Hydrological Model

PubMed Central

Ryo, Masahiro; Iwasaki, Yuichi; Yoshimura, Chihiro; Saavedra V., Oliver C.

2015-01-01

Alteration of the spatial variability of natural flow regimes has been less studied than that of the temporal variability, despite its ecological importance for river ecosystems. Here, we aimed to quantify the spatial patterns of flow regime alterations along a river network in the Sagami River, Japan, by estimating river discharge under natural and altered flow conditions. We used a distributed hydrological model, which simulates hydrological processes spatiotemporally, to estimate 20-year daily river discharge along the river network. Then, 33 hydrologic indices (i.e., Indicators of Hydrologic Alteration) were calculated from the simulated discharge to estimate the spatial patterns of their alterations. Some hydrologic indices were relatively well estimated such as the magnitude and timing of maximum flows, monthly median flows, and the frequency of low and high flow pulses. The accuracy was evaluated with correlation analysis (r > 0.4) and the Kolmogorov–Smirnov test (α = 0.05) by comparing these indices calculated from both observed and simulated discharge. The spatial patterns of the flow regime alterations varied depending on the hydrologic indices. For example, both the median flow in August and the frequency of high flow pulses were reduced by the maximum of approximately 70%, but these strongest alterations were detected at different locations (i.e., on the mainstream and the tributary, respectively). These results are likely caused by different operational purposes of multiple water control facilities. The results imply that the evaluation only at discharge gauges is insufficient to capture the alteration of the flow regime. Our findings clearly emphasize the importance of evaluating the spatial pattern of flow regime alteration on a river network where its discharge is affected by multiple water control facilities. PMID:26207997

Perceptual learning improves contrast sensitivity, visual acuity, and foveal crowding in amblyopia.

PubMed

Barollo, Michele; Contemori, Giulio; Battaglini, Luca; Pavan, Andrea; Casco, Clara

2017-01-01

Amblyopic observers present abnormal spatial interactions between a low-contrast sinusoidal target and high-contrast collinear flankers. It has been demonstrated that perceptual learning (PL) can modulate these low-level lateral interactions, resulting in improved visual acuity and contrast sensitivity. We measured the extent and duration of generalization effects to various spatial tasks (i.e., visual acuity, Vernier acuity, and foveal crowding) through PL on the target's contrast detection. Amblyopic observers were trained on a contrast-detection task for a central target (i.e., a Gabor patch) flanked above and below by two high-contrast Gabor patches. The pre- and post-learning tasks included lateral interactions at different target-to-flankers separations (i.e., 2, 3, 4, 8λ) and included a range of spatial frequencies and stimulus durations as well as visual acuity, Vernier acuity, contrast-sensitivity function, and foveal crowding. The results showed that perceptual training reduced the target's contrast-detection thresholds more for the longest target-to-flanker separation (i.e., 8λ). We also found generalization of PL to different stimuli and tasks: contrast sensitivity for both trained and untrained spatial frequencies, visual acuity for Sloan letters, and foveal crowding, and partially for Vernier acuity. Follow-ups after 5-7 months showed not only complete maintenance of PL effects on visual acuity and contrast sensitivity function but also further improvement in these tasks. These results suggest that PL improves facilitatory lateral interactions in amblyopic observers, which usually extend over larger separations than in typical foveal vision. The improvement in these basic visual spatial operations leads to a more efficient capability of performing spatial tasks involving high levels of visual processing, possibly due to the refinement of bottom-up and top-down networks of visual areas.

Quantitative analysis of biological tissues using Fourier transform-second-harmonic generation imaging

NASA Astrophysics Data System (ADS)

Ambekar Ramachandra Rao, Raghu; Mehta, Monal R.; Toussaint, Kimani C., Jr.

2010-02-01

We demonstrate the use of Fourier transform-second-harmonic generation (FT-SHG) imaging of collagen fibers as a means of performing quantitative analysis of obtained images of selected spatial regions in porcine trachea, ear, and cornea. Two quantitative markers, preferred orientation and maximum spatial frequency are proposed for differentiating structural information between various spatial regions of interest in the specimens. The ear shows consistent maximum spatial frequency and orientation as also observed in its real-space image. However, there are observable changes in the orientation and minimum feature size of fibers in the trachea indicating a more random organization. Finally, the analysis is applied to a 3D image stack of the cornea. It is shown that the standard deviation of the orientation is sensitive to the randomness in fiber orientation. Regions with variations in the maximum spatial frequency, but with relatively constant orientation, suggest that maximum spatial frequency is useful as an independent quantitative marker. We emphasize that FT-SHG is a simple, yet powerful, tool for extracting information from images that is not obvious in real space. This technique can be used as a quantitative biomarker to assess the structure of collagen fibers that may change due to damage from disease or physical injury.

Theta and Alpha Oscillations Are Traveling Waves in the Human Neocortex.

PubMed

Zhang, Honghui; Watrous, Andrew J; Patel, Ansh; Jacobs, Joshua

2018-06-01

Human cognition requires the coordination of neural activity across widespread brain networks. Here, we describe a new mechanism for large-scale coordination in the human brain: traveling waves of theta and alpha oscillations. Examining direct brain recordings from neurosurgical patients performing a memory task, we found contiguous clusters of cortex in individual patients with oscillations at specific frequencies within 2 to 15 Hz. These oscillatory clusters displayed spatial phase gradients, indicating that they formed traveling waves that propagated at ∼0.25-0.75 m/s. Traveling waves were relevant behaviorally because their propagation correlated with task events and was more consistent when subjects performed the task well. Human traveling theta and alpha waves can be modeled by a network of coupled oscillators because the direction of wave propagation correlated with the spatial orientation of local frequency gradients. Our findings suggest that oscillations support brain connectivity by organizing neural processes across space and time. Copyright © 2018 Elsevier Inc. All rights reserved.

Methods for magnetic resonance analysis using magic angle technique

DOEpatents

Hu, Jian Zhi [Richland, WA; Wind, Robert A [Kennewick, WA; Minard, Kevin R [Kennewick, WA; Majors, Paul D [Kennewick, WA

2011-11-22

Methods of performing a magnetic resonance analysis of a biological object are disclosed that include placing the object in a main magnetic field (that has a static field direction) and in a radio frequency field; rotating the object at a frequency of less than about 100 Hz around an axis positioned at an angle of about 54.degree.44' relative to the main magnetic static field direction; pulsing the radio frequency to provide a sequence that includes a phase-corrected magic angle turning pulse segment; and collecting data generated by the pulsed radio frequency. In particular embodiments the method includes pulsing the radio frequency to provide at least two of a spatially selective read pulse, a spatially selective phase pulse, and a spatially selective storage pulse. Further disclosed methods provide pulse sequences that provide extended imaging capabilities, such as chemical shift imaging or multiple-voxel data acquisition.

Soft X-ray holographic grating beam splitter including a double frequency grating for interferometer pre-alignment.

PubMed

Liu, Ying; Tan, Xin; Liu, Zhengkun; Xu, Xiangdong; Hong, Yilin; Fu, Shaojun

2008-09-15

Grating beam splitters have been fabricated for soft X-ray Mach- Zehnder interferometer using holographic interference lithography. The grating beam splitter consists of two gratings, one works at X-ray laser wavelength of 13.9 nm with the spatial frequency of 1000 lines/mm as the operation grating, the other works at visible wavelength of 632.8 nm for pre-aligning the X-ray interferometer with the spatial frequency of 22 lines/mm as the pre-alignment grating. The two gratings lie vertically on the same substrate. The main feature of the beam splitter is the use of low-spatial- frequency beat grating of a holographic double frequency grating as the pre-alignment grating of the X-ray interferometer. The grating line parallelism between the two gratings can be judged by observing the diffraction patterns of the pre-alignment grating directly.

FIBRE AND INTEGRATED OPTICS. OPTICAL PROCESSING OF INFORMATION: Method for optical data processing based on a two-pulse photon echo

NASA Astrophysics Data System (ADS)

Zakharov, S. M.; Manykin, Eduard A.

1995-02-01

The principles of optical processing based on dynamic spatial—temporal properties of two-pulse photon echo signals are considered. The properties of a resonant medium as an on-line filter of temporal and spatial frequencies are discussed. These properties are due to the sensitivity of such a medium to the Fourier spectrum of the second exiting pulse. Degeneracy of quantum resonant systems, demonstrated by the coherent response dependence on the square of the amplitude of the second pulse, can be used for 'simultaneous' correlation processing of optical 'signals'. Various methods for the processing of the Fourier optical image are discussed.

Low-dose cone-beam CT via raw counts domain low-signal correction schemes: Performance assessment and task-based parameter optimization (Part II. Task-based parameter optimization).

PubMed

Gomez-Cardona, Daniel; Hayes, John W; Zhang, Ran; Li, Ke; Cruz-Bastida, Juan Pablo; Chen, Guang-Hong

2018-05-01

Different low-signal correction (LSC) methods have been shown to efficiently reduce noise streaks and noise level in CT to provide acceptable images at low-radiation dose levels. These methods usually result in CT images with highly shift-variant and anisotropic spatial resolution and noise, which makes the parameter optimization process highly nontrivial. The purpose of this work was to develop a local task-based parameter optimization framework for LSC methods. Two well-known LSC methods, the adaptive trimmed mean (ATM) filter and the anisotropic diffusion (AD) filter, were used as examples to demonstrate how to use the task-based framework to optimize filter parameter selection. Two parameters, denoted by the set P, for each LSC method were included in the optimization problem. For the ATM filter, these parameters are the low- and high-signal threshold levels p l and p h ; for the AD filter, the parameters are the exponents δ and γ in the brightness gradient function. The detectability index d' under the non-prewhitening (NPW) mathematical observer model was selected as the metric for parameter optimization. The optimization problem was formulated as an unconstrained optimization problem that consisted of maximizing an objective function d'(P), where i and j correspond to the i-th imaging task and j-th spatial location, respectively. Since there is no explicit mathematical function to describe the dependence of d' on the set of parameters P for each LSC method, the optimization problem was solved via an experimentally measured d' map over a densely sampled parameter space. In this work, three high-contrast-high-frequency discrimination imaging tasks were defined to explore the parameter space of each of the LSC methods: a vertical bar pattern (task I), a horizontal bar pattern (task II), and a multidirectional feature (task III). Two spatial locations were considered for the analysis, a posterior region-of-interest (ROI) located within the noise streaks region and an anterior ROI, located further from the noise streaks region. Optimal results derived from the task-based detectability index metric were compared to other operating points in the parameter space with different noise and spatial resolution trade-offs. The optimal operating points determined through the d' metric depended on the interplay between the major spatial frequency components of each imaging task and the highly shift-variant and anisotropic noise and spatial resolution properties associated with each operating point in the LSC parameter space. This interplay influenced imaging performance the most when the major spatial frequency component of a given imaging task coincided with the direction of spatial resolution loss or with the dominant noise spatial frequency component; this was the case of imaging task II. The performance of imaging tasks I and III was influenced by this interplay in a smaller scale than imaging task II, since the major frequency component of task I was perpendicular to imaging task II, and because imaging task III did not have strong directional dependence. For both LSC methods, there was a strong dependence of the overall d' magnitude and shape of the contours on the spatial location within the phantom, particularly for imaging tasks II and III. The d' value obtained at the optimal operating point for each spatial location and imaging task was similar when comparing the LSC methods studied in this work. A local task-based detectability framework to optimize the selection of parameters for LSC methods was developed. The framework takes into account the potential shift-variant and anisotropic spatial resolution and noise properties to maximize the imaging performance of the CT system. Optimal parameters for a given LSC method depend strongly on the spatial location within the image object. © 2018 American Association of Physicists in Medicine.

Gate line edge roughness amplitude and frequency variation effects on intra die MOS device characteristics

NASA Astrophysics Data System (ADS)

Hamadeh, Emad; Gunther, Norman G.; Niemann, Darrell; Rahman, Mahmud

2006-06-01

Random fluctuations in fabrication process outcomes such as gate line edge roughness (LER) give rise to corresponding fluctuations in scaled down MOS device characteristics. A thermodynamic-variational model is presented to study the effects of LER on threshold voltage and capacitance of sub-50 nm MOS devices. Conceptually, we treat the geometric definition of the MOS devices on a die as consisting of a collection of gates. In turn, each of these gates has an area, A, and a perimeter, P, defined by nominally straight lines subject to random process outcomes producing roughness. We treat roughness as being deviations from straightness consisting of both transverse amplitude and longitudinal wavelength each having lognormal distribution. We obtain closed-form expressions for variance of threshold voltage ( Vth), and device capacitance ( C) at Onset of Strong Inversion (OSI) for a small device. Using our variational model, we characterized the device electrical properties such as σ and σC in terms of the statistical parameters of the roughness amplitude and spatial frequency, i.e., inverse roughness wavelength. We then verified our model with numerical analysis of Vth roll-off for small devices and σ due to dopant fluctuation. Our model was also benchmarked against TCAD of σ as a function of LER. We then extended our analysis to predict variations in σ and σC versus average LER spatial frequency and amplitude, and oxide-thickness. Given the intuitive expectation that LER of very short wavelengths must also have small amplitude, we have investigated the case in which the amplitude mean is inversely related to the frequency mean. We compare with the situation in which amplitude and frequency mean are unrelated. Given also that the gate perimeter may consist of different LER signature for each side, we have extended our analysis to the case when the LER statistical difference between gate sides is moderate, as well as when it is significantly large.

Spatial filtering velocimeter for vehicle navigation with extended measurement range

NASA Astrophysics Data System (ADS)

He, Xin; Zhou, Jian; Nie, Xiaoming; Long, Xingwu

2015-05-01

The idea of using spatial filtering velocimeter is proposed to provide accurate velocity information for vehicle autonomous navigation system. The presented spatial filtering velocimeter is based on a CMOS linear image sensor. The limited frame rate restricts high speed measurement of the vehicle. To extend measurement range of the velocimeter, a method of frequency shifting is put forward. Theoretical analysis shows that the frequency of output signal can be reduced and the measurement range can be doubled by this method when the shifting direction is set the same with that of image velocity. The approach of fast Fourier transform (FFT) is employed to obtain the power spectra of the spatially filtered signals. Because of limited frequency resolution of FFT, a frequency spectrum correction algorithm, called energy centrobaric correction, is used to improve the frequency resolution. The correction accuracy energy centrobaric correction is analyzed. Experiments are carried out to measure the moving surface of a conveyor belt. The experimental results show that the maximum measurable velocity is about 800deg/s without frequency shifting, 1600deg/s with frequency shifting, when the frame rate of the image is about 8117 Hz. Therefore, the measurement range is doubled by the method of frequency shifting. Furthermore, experiments were carried out to measure the vehicle velocity simultaneously using both the designed SFV and a laser Doppler velocimeter (LDV). The measurement results of the presented SFV are coincident with that of the LDV, but with bigger fluctuation. Therefore, it has the potential of application to vehicular autonomous navigation.

Psychophysical and physiological responses to gratings with luminance and chromatic components of different spatial frequencies.

PubMed

Cooper, Bonnie; Sun, Hao; Lee, Barry B

2012-02-01

Gratings that contain luminance and chromatic components of different spatial frequencies were used to study the segregation of signals in luminance and chromatic pathways. Psychophysical detection and discrimination thresholds to these compound gratings, with luminance and chromatic components of the one either half or double the spatial frequency of the other, were measured in human observers. Spatial frequency tuning curves for detection of compound gratings followed the envelope of those for luminance and chromatic gratings. Different grating types were discriminable at detection threshold. Fourier analysis of physiological responses of macaque retinal ganglion cells to compound waveforms showed chromatic information to be restricted to the parvocellular pathway and luminance information to the magnocellular pathway. Taken together, the human psychophysical and macaque physiological data support the strict segregation of luminance and chromatic information in independent channels, with the magnocellular and parvocellular pathways, respectively, serving as likely the physiological substrates. © 2012 Optical Society of America

Achieving pattern uniformity in plasmonic lithography by spatial frequency selection

NASA Astrophysics Data System (ADS)

Liang, Gaofeng; Chen, Xi; Zhao, Qing; Guo, L. Jay

2018-01-01

The effects of the surface roughness of thin films and defects on photomasks are investigated in two representative plasmonic lithography systems: thin silver film-based superlens and multilayer-based hyperbolic metamaterial (HMM). Superlens can replicate arbitrary patterns because of its broad evanescent wave passband, which also makes it inherently vulnerable to the roughness of the thin film and imperfections of the mask. On the other hand, the HMM system has spatial frequency filtering characteristics and its pattern formation is based on interference, producing uniform and stable periodic patterns. In this work, we show that the HMM system is more immune to such imperfections due to its function of spatial frequency selection. The analyses are further verified by an interference lithography system incorporating the photoresist layer as an optical waveguide to improve the aspect ratio of the pattern. It is concluded that a system capable of spatial frequency selection is a powerful method to produce deep-subwavelength periodic patterns with high degree of uniformity and fidelity.

Detection of radial motion depends on spatial displacement.

PubMed

de la Malla, Cristina; López-Moliner, Joan

2010-06-01

Nakayama and Tyler (1981) disentangled the use of pure motion (speed) information from spatial displacement information for the detection of lateral motion. They showed that when positional cues were removed the contribution of motion or spatial information was dependent on the temporal frequency: for temporal frequencies lower than 1Hz the mechanism used to detect motion relied on speed information while for higher temporal frequencies a mechanism based on displacement information was used. Here we test whether the same dependency is also revealed in radial motion. In order to do so, we adapted the paradigm previously used by Nakayama and Tyler to obtain detection thresholds for lateral and radial motion by using a 2-IFC procedure. Subjects had to report which of the intervals contained the signal stimulus (33% coherent motion). We replicated the temporal frequency dependency for lateral motion but results indicate, however, that the detection of radial is always consistent with detecting a spatial displacement amplitude. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

The role of low-spatial frequencies in lexical decision and masked priming.

PubMed

Boden, C; Giaschi, D

2009-04-01

Spatial frequency filtering was used to test the hypotheses that low-spatial frequency information in printed text can: (1) lead to a rapid lexical decision or (2) facilitate word recognition. Adult proficient readers made lexical decisions in unprimed and masked repetition priming experiments with unfiltered, low-pass, high-pass and notch filtered letter strings. In the unprimed experiments, a filtered target was presented for 105 or 400 ms followed by a pattern mask. Sensitivity (d') was lowest for the low-pass filtered targets at both durations with a bias towards a 'non-word' response. Sensitivity was higher in the high-pass and notch filter conditions. In the priming experiments, a forward mask was followed by a filtered prime then an unfiltered target. Primed words, but not non-words, were identified faster than unprimed words in both the low-pass and high-pass filtered conditions. These results do not support a unique role for low-spatial frequency information in either facilitating or making rapid lexical decisions.

Spatial-frequency requirements for reading revisited

PubMed Central

Kwon, MiYoung; Legge, Gordon E.

2012-01-01

Blur is one of many visual factors that can limit reading in both normal and low vision. Legge et al. [Legge, G. E., Pelli, D. G., Rubin, G. S., & Schleske, M. M. (1985). Psychophysics of reading. I. Normal vision. Vision Research, 25, 239–252.] measured reading speed for text that was low-pass filtered with a range of cutoff spatial frequencies. Above 2 cycles per letter (CPL) reading speed was constant at its maximum level, but decreased rapidly for lower cutoff frequencies. It remains unknown why the critical cutoff for reading speed is near 2 CPL. The goal of the current study was to ask whether the spatial-frequency requirement for rapid reading is related to the effects of cutoff frequency on letter recognition and the size of the visual span. Visual span profiles were measured by asking subjects to recognize letters in trigrams (random strings of three letters) flashed for 150 ms at varying letter positions left and right of the fixation point. Reading speed was measured with Rapid Serial Visual Presentation (RSVP). The size of the visual span and reading speed were measured for low-pass filtered stimuli with cutoff frequencies from 0.8 to 8 CPL. Low-pass letter recognition data, obtained under similar testing conditions, were available from our previous study (Kwon & Legge, 2011). We found that the spatial-frequency requirement for reading is very similar to the spatial-frequency requirements for the size of the visual span and single letter recognition. The critical cutoff frequencies for reading speed, the size of the visual span and a contrast-invariant measure of letter recognition were all near 1.4 CPL, which is lower than the previous estimate of 2 CPL for reading speed. Although correlational in nature, these results are consistent with the hypothesis that the size of the visual span is closely linked to reading speed. PMID:22521659

Magnetic Resonance Characterization of Axonal Response to Spinal Cord Injury

DTIC Science & Technology

2012-10-01

frequency direction, phase FOV = 0.5, slice thickness = 10 mm. Spatial saturation bands were placed anterior and posterior to the slice of interest to...thickness = 10 mm, with spatial saturation bands placed anterior and posterior to the slice and diffusion sensitization in the right-to-left...the center frequency, and can be extracted by applying MT saturation pulses with alternating (positive/negative) off-resonance frequencies. The goal

Laser Controlled Tunneling in a Vertical Optical Lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaufils, Q.; Tackmann, G.; Wang, X.

2011-05-27

Raman laser pulses are used to induce coherent tunneling between neighboring sites of a vertical 1D optical lattice. Such tunneling occurs when the detuning of a probe laser from the atomic transition frequency matches multiples of the Bloch frequency, allowing for a spectroscopic control of the coupling between Wannier-Stark (WS) states. In particular, we prepare coherent superpositions of WS states of adjacent sites, and investigate the coherence time of these superpositions by realizing a spatial interferometer. This scheme provides a powerful tool for coherent manipulation of external degrees of freedom of cold atoms, which is a key issue for quantummore » information processing.« less

Causal implication by rhythmic transcranial magnetic stimulation of alpha frequency in feature-based local vs. global attention.

PubMed

Romei, Vincenzo; Thut, Gregor; Mok, Robert M; Schyns, Philippe G; Driver, Jon

2012-03-01

Although oscillatory activity in the alpha band was traditionally associated with lack of alertness, more recent work has linked it to specific cognitive functions, including visual attention. The emerging method of rhythmic transcranial magnetic stimulation (TMS) allows causal interventional tests for the online impact on performance of TMS administered in short bursts at a particular frequency. TMS bursts at 10 Hz have recently been shown to have an impact on spatial visual attention, but any role in featural attention remains unclear. Here we used rhythmic TMS at 10 Hz to assess the impact on attending to global or local components of a hierarchical Navon-like stimulus (D. Navon (1977) Forest before trees: The precedence of global features in visual perception. Cognit. Psychol., 9, 353), in a paradigm recently used with TMS at other frequencies (V. Romei, J. Driver, P.G. Schyns & G. Thut. (2011) Rhythmic TMS over parietal cortex links distinct brain frequencies to global versus local visual processing. Curr. Biol., 2, 334-337). In separate groups, left or right posterior parietal sites were stimulated at 10 Hz just before presentation of the hierarchical stimulus. Participants had to identify either the local or global component in separate blocks. Right parietal 10 Hz stimulation (vs. sham) significantly impaired global processing without affecting local processing, while left parietal 10 Hz stimulation vs. sham impaired local processing with a minor trend to enhance global processing. These 10 Hz outcomes differed significantly from stimulation at other frequencies (i.e. 5 or 20 Hz) over the same site in other recent work with the same paradigm. These dissociations confirm differential roles of the two hemispheres in local vs. global processing, and reveal a frequency-specific role for stimulation in the alpha band for regulating feature-based visual attention. © 2012 The Authors. European Journal of Neuroscience © 2012 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.

RF stabilization of plasma instabilities: a note on physical mechanism

NASA Astrophysics Data System (ADS)

Sen, S.; Martinell, J.; Imadera, K.; Kishimoto, Y.; Vahala, G.

2018-02-01

In a series of recent works, we have developed models including realistic spatial profiles of both flow and radio-frequency-induced ponderomotive force. With these inclusions, the picture of stability of various plasma and fluid instabilities is expected to be changed drastically with ground-breaking consequences. The inhomogeneous parallel flow and the radio-frequency waves can actually stabilize turbulence. This is different from the prevalent notion that both parallel flow shear and radio-frequency waves are responsible for the excitation (destabilization) of plasma turbulence. This model thus aims to open-up new channels and provide a major breakthrough in our knowledge of plasma and fluid turbulence and its consequent roles in energy, space and processing technology. In this short note, we elucidate the physical mechanism behind this novel observation.

Space/Frequency Conversions in Image Processing and Transmission.

DTIC Science & Technology

1981-11-01

particularly with respect to the signal-to- noise ratio of the processed outputs. Devejlmnnt 9i a 1megtg fO-g s *&t~i egM2&Y conversion image_ aEggMsinLg: One...slowiv, whil e tle spatial impulse r-on i Ix~v; t) is vairied rapidly Iit *I tat tern recognitiont steartcl operaitioti. Under thiese c’irc-umstances, 11...electronic) will he incapable of recording the image with good signal-to- noise ratio. In what follows, we consider two approaches to producing these

Top-down beta oscillatory signaling conveys behavioral context in early visual cortex.

PubMed

Richter, Craig G; Coppola, Richard; Bressler, Steven L

2018-05-03

Top-down modulation of sensory processing is a critical neural mechanism subserving numerous important cognitive roles, one of which may be to inform lower-order sensory systems of the current 'task at hand' by conveying behavioral context to these systems. Accumulating evidence indicates that top-down cortical influences are carried by directed interareal synchronization of oscillatory neuronal populations, with recent results pointing to beta-frequency oscillations as particularly important for top-down processing. However, it remains to be determined if top-down beta-frequency oscillations indeed convey behavioral context. We measured spectral Granger Causality (sGC) using local field potentials recorded from microelectrodes chronically implanted in visual areas V1/V2, V4, and TEO of two rhesus macaque monkeys, and applied multivariate pattern analysis to the spatial patterns of top-down sGC. We decoded behavioral context by discriminating patterns of top-down (V4/TEO-to-V1/V2) beta-peak sGC for two different task rules governing correct responses to identical visual stimuli. The results indicate that top-down directed influences are carried to visual cortex by beta oscillations, and differentiate task demands even before visual stimulus processing. They suggest that top-down beta-frequency oscillatory processes coordinate processing of sensory information by conveying global knowledge states to early levels of the sensory cortical hierarchy independently of bottom-up stimulus-driven processing.

Individual differences in cardiac vagal tone are associated with differential neural responses to facial expressions at different spatial frequencies: an ERP and sLORETA study.

PubMed

Park, Gewnhi; Moon, Eunok; Kim, Do-Won; Lee, Seung-Hwan

2012-12-01

A previous study has shown that greater cardiac vagal tone, reflecting effective self-regulatory capacity, was correlated with superior visual discrimination of fearful faces at high spatial frequency Park et al. (Biological Psychology 90:171-178, 2012b). The present study investigated whether individual differences in cardiac vagal tone (indexed by heart rate variability) were associated with different event-related brain potentials (ERPs) in response to fearful and neutral faces. Thirty-six healthy participants discriminated the emotion of fearful and neutral faces at broad, high, and low spatial frequencies, while ERPs were recorded. Participants with low resting heart rate variability-characterized by poor functioning of regulatory systems-exhibited significantly greater N200 activity in response to fearful faces at low spatial frequency and greater LPP responses to neutral faces at high spatial frequency. Source analyses-estimated by standardized low-resolution brain electromagnetic tomography (sLORETA)-tended to show that participants with low resting heart rate variability exhibited increased source activity in visual areas, such as the cuneus and the middle occipital gyrus, as compared with participants with high resting heart rate variability. The hyperactive neural activity associated with low cardiac vagal tone may account for hypervigilant response patterns and emotional dysregulation, which heightens the risk of developing physical and emotional problems.

Optical pathology of human brain metastasis of lung cancer using combined resonance Raman and spatial frequency spectroscopies

NASA Astrophysics Data System (ADS)

Zhou, Yan; Liu, Cheng-hui; Pu, Yang; Cheng, Gangge; Zhou, Lixin; Chen, Jun; Zhu, Ke; Alfano, Robert R.

2016-03-01

Raman spectroscopy has become widely used for diagnostic purpose of breast, lung and brain cancers. This report introduced a new approach based on spatial frequency spectra analysis of the underlying tissue structure at different stages of brain tumor. Combined spatial frequency spectroscopy (SFS), Resonance Raman (RR) spectroscopic method is used to discriminate human brain metastasis of lung cancer from normal tissues for the first time. A total number of thirty-one label-free micrographic images of normal and metastatic brain cancer tissues obtained from a confocal micro- Raman spectroscopic system synchronously with examined RR spectra of the corresponding samples were collected from the identical site of tissue. The difference of the randomness of tissue structures between the micrograph images of metastatic brain tumor tissues and normal tissues can be recognized by analyzing spatial frequency. By fitting the distribution of the spatial frequency spectra of human brain tissues as a Gaussian function, the standard deviation, σ, can be obtained, which was used to generate a criterion to differentiate human brain cancerous tissues from the normal ones using Support Vector Machine (SVM) classifier. This SFS-SVM analysis on micrograph images presents good results with sensitivity (85%), specificity (75%) in comparison with gold standard reports of pathology and immunology. The dual-modal advantages of SFS combined with RR spectroscopy method may open a new way in the neuropathology applications.

A Sparsity-Based Approach to 3D Binaural Sound Synthesis Using Time-Frequency Array Processing

NASA Astrophysics Data System (ADS)

Cobos, Maximo; Lopez, JoseJ; Spors, Sascha

2010-12-01

Localization of sounds in physical space plays a very important role in multiple audio-related disciplines, such as music, telecommunications, and audiovisual productions. Binaural recording is the most commonly used method to provide an immersive sound experience by means of headphone reproduction. However, it requires a very specific recording setup using high-fidelity microphones mounted in a dummy head. In this paper, we present a novel processing framework for binaural sound recording and reproduction that avoids the use of dummy heads, which is specially suitable for immersive teleconferencing applications. The method is based on a time-frequency analysis of the spatial properties of the sound picked up by a simple tetrahedral microphone array, assuming source sparseness. The experiments carried out using simulations and a real-time prototype confirm the validity of the proposed approach.

Digital processing of radiographic images

NASA Technical Reports Server (NTRS)

Bond, A. D.; Ramapriyan, H. K.

1973-01-01

Some techniques are presented and the software documentation for the digital enhancement of radiographs. Both image handling and image processing operations are considered. The image handling operations dealt with are: (1) conversion of format of data from packed to unpacked and vice versa; (2) automatic extraction of image data arrays; (3) transposition and 90 deg rotations of large data arrays; (4) translation of data arrays for registration; and (5) reduction of the dimensions of data arrays by integral factors. Both the frequency and the spatial domain approaches are presented for the design and implementation of the image processing operation. It is shown that spatial domain recursive implementation of filters is much faster than nonrecursive implementations using fast fourier transforms (FFT) for the cases of interest in this work. The recursive implementation of a class of matched filters for enhancing image signal to noise ratio is described. Test patterns are used to illustrate the filtering operations. The application of the techniques to radiographic images of metallic structures is demonstrated through several examples.

Automated processing for proton spectroscopic imaging using water reference deconvolution.

PubMed

Maudsley, A A; Wu, Z; Meyerhoff, D J; Weiner, M W

1994-06-01

Automated formation of MR spectroscopic images (MRSI) is necessary before routine application of these methods is possible for in vivo studies; however, this task is complicated by the presence of spatially dependent instrumental distortions and the complex nature of the MR spectrum. A data processing method is presented for completely automated formation of in vivo proton spectroscopic images, and applied for analysis of human brain metabolites. This procedure uses the water reference deconvolution method (G. A. Morris, J. Magn. Reson. 80, 547(1988)) to correct for line shape distortions caused by instrumental and sample characteristics, followed by parametric spectral analysis. Results for automated image formation were found to compare favorably with operator dependent spectral integration methods. While the water reference deconvolution processing was found to provide good correction of spatially dependent resonance frequency shifts, it was found to be susceptible to errors for correction of line shape distortions. These occur due to differences between the water reference and the metabolite distributions.

Complex mode indication function and its applications to spatial domain parameter estimation

NASA Astrophysics Data System (ADS)

Shih, C. Y.; Tsuei, Y. G.; Allemang, R. J.; Brown, D. L.

1988-10-01

This paper introduces the concept of the Complex Mode Indication Function (CMIF) and its application in spatial domain parameter estimation. The concept of CMIF is developed by performing singular value decomposition (SVD) of the Frequency Response Function (FRF) matrix at each spectral line. The CMIF is defined as the eigenvalues, which are the square of the singular values, solved from the normal matrix formed from the FRF matrix, [ H( jω)] H[ H( jω)], at each spectral line. The CMIF appears to be a simple and efficient method for identifying the modes of the complex system. The CMIF identifies modes by showing the physical magnitude of each mode and the damped natural frequency for each root. Since multiple reference data is applied in CMIF, repeated roots can be detected. The CMIF also gives global modal parameters, such as damped natural frequencies, mode shapes and modal participation vectors. Since CMIF works in the spatial domain, uneven frequency spacing data such as data from spatial sine testing can be used. A second-stage procedure for accurate damped natural frequency and damping estimation as well as mode shape scaling is also discussed in this paper.

Effects of variations of stage and flux at different frequencies on the estimates using river stage tomography

NASA Astrophysics Data System (ADS)

Wang, Y. L.; Yeh, T. C. J.; Wen, J. C.

2017-12-01

This study is to investigate the ability of river stage tomography to estimate the spatial distribution of hydraulic transmissivity (T), storage coefficient (S), and diffusivity (D) in groundwater basins using information of groundwater level variations induced by periodic variations of stream stage, and infiltrated flux from the stream boundary. In order to accomplish this objective, the sensitivity and correlation of groundwater heads with respect to the hydraulic properties is first conducted to investigate the spatial characteristics of groundwater level in response to the stream variations at different frequencies. Results of the analysis show that the spatial distributions of the sensitivity of heads at an observation well in response to periodic river stage variations are highly correlated despite different frequencies. On the other hand, the spatial patterns of the sensitivity of the observed head to river flux boundaries at different frequencies are different. Specifically, the observed head is highly correlated with T at the region between the stream and observation well when the high-frequency periodic flux is considered. On the other hand, it is highly correlated with T at the region between monitoring well and the boundary opposite to the stream when the low-frequency periodic flux is prescribed to the stream. We also find that the spatial distributions of the sensitivity of observed head to S variation are highly correlated with all frequencies in spite of heads or fluxes stream boundary. Subsequently, the differences of the spatial correlations of the observed heads to the hydraulic properties under the head and flux boundary conditions are further investigated by an inverse model (i.e., successive stochastic linear estimator). This investigation uses noise-free groundwater and stream data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of river stage tomography is then tested with these synthetic data sets to estimate T, S, and D distribution. The results reveal that boundary flux variations with different frequencies contain different information about the aquifer characteristics while the head boundary does not.