bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integration of Disparity Information across Multiple Fixations
Authors: Sumnall J H , Cumming B G , Parker A J 
Published: December 2015

We measured stereo thresholds for observers viewing noisy, dynamic random-dot stereograms (DRDS) containing either a spatial or a temporal step in depth. Stereograms were presented either with or without a small fixation cross at zero disparity. When the fixation marker was present observers were instructed to maintain fixation throughout the presentation. For spatial steps in depth, the lowest thresholds were found when there was no fixation marker and observers were free to look around the stimulus. Thresholds were higher with a fixation marker in the stimulus. The opposite pattern of results was found for stimuli that contained a temporal step in depth, ie the lowest thresholds were found with a fixation marker. Furthermore, presentation of a single depth region with a fixation marker gave the lowest thresholds of any configuration tested. The results with temporal changes in depth are reminiscent of the findings of Westheimer (1979 Experimental Brain Research36 585 – 597). Westheimer argued that sequential presentation in the same location might depress sensitivity to changes in depth, but in DRDS no single dot changes in depth without also changing in retinal location, so this explanation is not applicable. We conclude that, with a spatial step in depth, it is advantageous to foveate both sides of the step, so multiple fixations help. With a temporal step in depth, the spatial structure of the stimulus is uniform, so multiple fixations may not necessarily help, especially if they result in uncertainty about vergence position.
Statistical Analysis of Spatial Structure in Natural Images
Authors: Watt R , Carlin P 
Published: December 2015

When a sample of natural images is taken and compared with a set of noise images, the two are obviously distinguishable. Even when the noise images are set to have the same power spectral characteristics as the natural images, there is no doubt which is a normal image and which is a noise image. In the study to be reported, we have examined the nature of the spatial characteristics of natural images that allow them to be so discriminated from noise images. The approach is to process large sets of images belonging to various categories through mechanisms that have some similarities to known operations in biological visual systems. Thus, the images are filtered at various spatial scales and at various orientations; the filter outputs are combined into local energy maps; and features are detected in such processed images. The result of these calculations is the distribution of values of some parameter which describes a particular image characteristics for each set of images. Parameters that could support adequate discrimination between two sets of images, for example natural images and noise images, will have largely non-overlapping distributions. In practice it is found that no simple parameters can distinguish obviously different sets of images, but parameters that encapsulate spatial patterns, especially those related to non-accidental image properties, can do so. It is concluded that filter outputs must be followed by nontrivial spatial operations. Suggestions are made as to what are the most plausible.
Natural-Image Discrimination in the Periphery: The Importance of Phase and Amplitude Information
Authors: Kennedy G M , Tolhurst D J 
Published: December 2015

Previous studies with simplified stimuli such as combinations of sinusoidal gratings have revealed phase identification losses in the periphery that are not eliminated by a scaling factor. How do these phase processing problems influence our ability to discriminate natural images in the periphery? In this study the ability of an observer to identify the ‘odd-image-out’ when there is either an amplitude-only, phase-only, or amplitude and phase change in one out of three stimuli is compared. Pairs of Fourier-manipulated black-and-white digitised photographs of natural images were used and phase and amplitude spectral exchanges of varying proportions were made between two different images. Measurements were made to determine the smallest phase change needed in order for the observer to reliably discriminate the manipulated image, compared to two reference stimuli, at eccentricities of 0°, 2.5°, 5°, and 10°. This was compared to discrimination thresholds found when amplitude and phase, and amplitude alone were exchanged. The ability to discriminate images on the basis of phase information alone did fall off quickly with eccentricity (comparable to phase and amplitude discriminations). However, there was a much more rapid decline in amplitude-only discrimination. It appears that phase information in natural scenes remains a relatively more important visual cue in the periphery than amplitude.
Spatio-Chromatic Information Content of Natural Scenes
Authors: Troscianko T , Parraga C A , Brelstaff G , Carr D , Nelson K 
Published: December 2015

A common assumption in the study of the relationship between human vision and the visual environment is that human vision has developed in order to encode the incident information in an optimal manner. Such arguments have been used to support the 1/f dependence of scene content as a function of spatial frequency. In keeping with this assumption, we ask whether there are any important differences between the luminance and (r/g) chrominance Fourier spectra of natural scenes, the simple expectation being that the chrominance spectrum should be relatively richer in low spatial frequencies than the luminance spectrum, to correspond with the different shape of luminance and chrominance contrast sensitivity functions. We analysed a data set of 29 images of natural scenes (predominantly of vegetation at different distances) which were obtained with a hyper-spectral camera (measuring the scene through a set of 31 wavelength bands in the range 400 – 700 nm). The images were transformed to the three Smith — Pokorny cone fundamentals, and further transformed into ‘luminance’ (r+g) and ‘chrominance’ (r-g) images, with various assumptions being made about the relative weighting of the r and g components, and the form of the chrominance response. We then analysed the Fourier spectra of these images using logarithmic intervals in spatial frequency space. This allowed a determination of the total energy within each Fourier band for each of the luminance and chrominance representations. The results strongly indicate that, for the set of scenes studied here, there was no evidence of a predominance of low-spatial-frequency chrominance information. Two classes of explanation are possible: (a) that raw Fourier content may not be the main organising principle determining visual encoding of colour, and/or (b) that our scenes were atypical of what may have driven visual evolution. We present arguments in favour of both of these propositions.
Image Region Labelling by Humans and by an Artificial Neural Network
Authors: Clark A , Troscianko T , Campbell N , Thomas B 
Published: December 2015

We reported (Troscianko et al, 1995 Perception24 Supplement, 18) that a neural network has been developed which is capable of labelling objects in natural scenes by first segmenting a scene, then obtaining a description of each segment in terms of a set of features. A neural net is then trained to label the segments on the basis of the feature set. The question we are now addressing is: how important is each of these features to overall performance, both in human and machine vision? We carried out an experiment in which human subjects were trained in the same labelling task as the neural net. Individual segments of scenes (sometimes corresponding to a whole object, eg a car, and sometimes an incomplete region, eg part of the sky) were presented on a screen, and the subject asked to label the scene as one of eleven possible types of object (sky, vegetation, vehicle …). Feedback was given and the learning curve monitored. When the learning curve was flat, each subject's performance was investigated with both intact and degraded stimuli. The degradation consisted of partial representation of the information, such as presenting just the outer boundary, or the average colour, or the average luminance, or randomising the size, position, and texture of the segment. The results suggest that this degradation produces significant changes in performance (F9,7=4.4, p=0.0005). A posteriori analysis indicates that certain attributes (particularly texture, boundary-only, colour-averaging) are particularly influential in mediating performance. A similar set of results was obtained by training the network on similarly degraded data. The results imply: (1) that a neural net can provide a useful model of human object labelling processes, and (2) that certain features are more important than others in mediating such performance.
Depth and Motion in Object Completion
Authors: Kellman P J , Shipley T F 
Published: December 2015

Models of illusory and occluded contour and surface completion have focused on static spatial relations in planar surfaces. We consider several findings indicating that depth and motion play important roles in object completion. In one set of studies, effects of depth separation were studied in a speeded classification paradigm in which surface pieces were oriented in parallel or convergent (intersecting) planes. Subjects' task was to respond “parallel” or “convergent” on each trial. It was hypothesised that object completion would facilitate performance, and that depth separation of the two visible areas would disrupt completion. Speed and accuracy were reliably reduced when object parts were separated in depth via stereoscopic information. In a second series of studies a speeded classification paradigm was used to test perception of illusory figures from edges specified solely by motion (accretion-deletion of texture). The aim of a third study was to test occluded object completion where the visible parts of the object were not simultaneously present, but revealed over time. Results showed reliable object completion effects when certain spatial and temporal relationships held among object parts. We discuss three elements of a revised theoretical model suggested by these results: (1) edge inputs to boundary completion processes need not be luminance edges—they may also be motion-specified edges; (2) the criterion of relatability governing edge interpolation processes must include depth relations as well as planar ones; (3) the criterion of relatability must be reformulated in terms of spatiotemporal, rather than merely spatial, relationships. Particulars of a new model that meets these conditions are briefly described.
Orientation Discrimination for Moving Isoluminant and Luminance Targets
Authors: Wuerger S M , Morgan M J 
Published: December 2015

Last year we presented orientation discrimination thresholds for stationary isoluminant red — green and luminance-defined stimuli as a function of spatial frequency and contrast (Wuerger and Morgan, 1995 Perception24 Supplement, 16). The horizontal profile of the stimuli was a Gabor function with a carrier frequency of either 0, 2, or 4 cycles deg−1. Observers made a binary decision (clockwise versus anticlockwise from vertical) and thresholds were defined as the standard deviation of their psychometric function. One main finding was that for carrier frequencies of 2 and 4 cycles deg−1, when stimuli of equal cone contrast are compared, orientation discrimination thresholds for red — green isoluminant stimuli do not differ significantly from the thresholds for luminance-defined stimuli. To further characterise the chromatic mechanisms involved in spatial vision, we assessed orientation discrimination thresholds for isoluminant red — green and luminance-defined Gabor stimuli as a function of the velocity of the moving target. When velocity is increased, orientation discrimination thresholds for isoluminant targets increase more rapidly than the thresholds for luminance targets of identical cone contrasts. We conclude that orientation discrimination is mediated by different chromatic mechanisms with different spatial and temporal sensitivities.
Anisotropy in Oriented-Line-Target Detection at High and Low Luminance Contrast
Authors: Doherty L M , Foster D H 
Published: December 2015

Observers can detect a uniquely oriented line segment (‘target’) in a background field of uniformly oriented line segments (‘nontargets’) even if viewing time is brief. When the lines have high luminance contrast, the variation of orientation increment threshold with nontarget orientation is periodic, generally with a period of about 90° although smaller periods have been found. Do the orientation-sensitive mechanisms giving rise to periodicities function only at high contrast? This question was addressed in a line-target detection experiment. Twenty white line segments of length 1 deg visual angle were presented in a circular field of diameter 20 deg visual angle. Nontarget orientations were in the range 0°, 5°, …, 175°, and the difference between nontarget and target orientations was varied adaptively. Stimulus displays lasting 40 ms were followed by a blank interstimulus interval lasting 60 ms and then a random-line mask. A view-tunnel provided a grey background of luminance 35 cd m−2 and stimulus contrast was 0.1, 0.3, 0.5, 0.7, or 0.9 log unit above the observer's luminance detection threshold for one line segment. When contrast was 0.1 log unit above this threshold, performance was near chance level. As contrast increased from 0.3 to 0.9 log unit above luminance detection threshold, performance improved and orientation increment thresholds decreased, showing that early orientation-processing is most effective at high luminance contrast. Nonetheless, periodicities were found in all conditions where performance was better than chance which suggests that the orientation-sensitive mechanisms associated with periodicities operate at both high and low luminance contrast.
Edge Assignment in Cells of Monkey Area V2
Authors: Zhou H , Friedman H , von der Heydt R 
Published: December 2015

One of the processes of visual perception is to organise 2-D images into figure and ground, assigning the borders to the figure. We have studied the neural basis of this phenomenon. We recorded from orientation-selective cells of areas V1 and V2 in the awake, fixating monkey. A square (typically 4 deg) of uniform colour or gray was displayed in a uniform surround field (11 deg) of different colour or gray. The square was much larger than the response fields of the cells studied. Its orientation and colour were optimised for each cell. In interleaved tests, we centred two opposite edges of the square in the RF, and also reversed the colours of square and surround, resulting in four different display combinations. Flipping edges and colours produced pairs of displays with an identical edge in the response field, but the figure on opposite sides. The display was static for each period of fixation, and mean spike numbers per second were measured. Many cells were selective for the sign of local contrast. In V2 we found cells that were highly discriminative for the direction of the figure, eg responding 10 times more to the left edge of a gray square with white surround than to the right edge of a white square with gray surround. In some cells, this discrimination was nearly independent of the figure size. The response could either be independent of local contrast (general edge assignment), or conditional on figure colour (joint assignment of edge and colour). We have observed direction-of-figure preference also in V1, but with smaller discrimination ratios. We conclude that figural edge assignment is part of early cortical processing.
Hand Action in a Radial Direction Captures Visual Motion in Depth
Authors: Ishimura G 
Published: December 2015

Transversal hand action in the frontoparallel plane biases the perception of bistable visual motion. This has been called action capture. In daily behaviour, however, hand action in a ‘radial’ direction from the head might be more important, because we frequently reach our hand for an object in front of us while guiding the action with vision. The purpose of this study was to measure the strength of action capture in the radial direction. Horizontal luminance gratings were placed above and below the fixation point. Binocular disparity, perspective contour, and spatial frequency gradient cues were attached to the gratings so that they simulated the ‘ceiling’ and the ‘floor’ of a long corridor. The display was reflected on a tilted mirror to face upward. The subject looked into the display and moved his/her dominant hand toward, or away from, the face behind the mirror. Just after the action onset, detected by the computer, one of the two gratings (the ceiling or the floor) flickered in short period to simulate bistable visual motion in depth (approaching or departing). The subject indicated the perceived motion direction in the frontoparallel plane using a 2AFC (upward or downward) method. The results showed that perceived motion was significantly biased to the ‘departing’ direction when the hand moved ‘away from’ the face, and it was biased to the ‘approaching’ direction when the hand moved ‘toward’ it. It is concluded that action capture occurs not only in transversal but also in radial movements.
Dynamic Structural Change of 3-D Illusory Surface Observed with Binocular Viewing
Authors: Idesawa M , Sakaguchi Y , Shimada Y 
Published: December 2015

When adequate visual stimuli are suitably arranged, for example, partially along the surface boundary or beyond the covering illusory surface, an opaque or transparent illusory surface can be seen (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 – 754; 30-7B L1289). By moving the visual stimuli of the occluding objects which were not physically depicted, several interesting phenomena have been observed. Dynamic fusion and separation of illusory surfaces have been observed when the visual stimuli were changed continuously between two different conditions; only one illusory surface was perceived in the first condition and two separate illusory surfaces were perceived in the second condition. Hysteresis was recognised in the geometrical positions between fusion and separation of the surfaces. In addition, elastically distorting illusory surfaces have been observed when the positions of two occluding objects, placed on opposite sides, were moved continuously in a sinusoidal way in opposite phase between two positions where the two illusory surfaces could not be bridged together when they were stationary. The phenomena have been observed both for opaque and for transparent illusory surfaces. They could be interpreted as reflections of the surface-perceiving process in our visual system. Probably our visual system tends to contain the previously perceived structure; then the transition from one structure to another is delayed until the geometrical conditions change sufficiently to break the previously perceived structure.
Fixation Disparity as a Function of Viewing Distance and Prism Load
Authors: Jaschinski W 
Published: December 2015

In binocular vision, fixation disparity is present when a fixation point falls within Panum's area, but not on corresponding retinal points. To investigate the effect of vergence load, fixation disparity was measured at viewing distances of 20, 30, 40, 60, and 100 cm (while the test subtended a constant angular size) by the psychophysical method of dichoptically presented nonius lines with a central fusion stimulus. As the viewing distance was shortened from 100 to 20 cm, mean fixation disparity changed monotonically from 1 min arc esophoria (ie the eyes converged in front of the target) to 3 min arc exophoria. The average standard deviation of the psychometric function, which is a measure of the temporal variability of vergence, was smallest at 100 cm (when fixation disparity was esophoric) and increased at shorter distances. Fixation disparity was also measured at a constant distance of 40 cm, but with prisms in front of the eyes that induced the same vergence angles as would be induced by viewing distances between 20 and 100 cm. The slope of these conventional ‘fixation disparity curves’ as a function of prism load correlated with the slope of fixation disparity as a function of viewing distance ( r=0.39, p=0.02, n=25). However, testing at different distances, as introduced here, has the advantage of preserving the natural interaction between vergence and accommodation. Since the change of fixation disparity with distance differed reliably among subjects (with a test — retest correlation of 0.65 in 34 subjects with good binocular vision) this measure may be useful for identifying subjects who are prone to near-vision complaints.
Intermodal Compensatory Effects in a Visual Search Task with Congenitally Deaf Adults
Authors: Stivalet P , Moreno Y , Cian C , Richard J , Barraud P-A 
Published: December 2015

In a visual search paradigm we measured the stimulus onset asynchrony (SOA) between a stimulus and a mask that was required to reach 90% correct responses. This procedure has the advantage of taking into account the real processing time and excluding the time for the generation of the motor response. Twelve congenitally deaf adult subjects and twelve normal subjects were given a visual search task for a target letter O among a varying number of distractor letters Q and vice-versa. In both groups we found the asymmetrical visual search pattern classically observed with parallel processing for the search for the target Q and with serial processing for the search for the target O (Treisman, 1985 Computer Vision, Graphics, and Image Processing31 156 – 177). The difference between the mean search slopes for an O target was not statistically significant between the groups; this might be due to the variability within the groups. The visual search amidst the congenitally deaf does not seem to benefit from a compensatory effect in relation to the acoustic deprivation. Our results seem to confirm data reported by Neville (1990 Annals of the New York Academy of Science 71 – 91) obtained by an electrophysiological technique based on event-related potentials. Nevertheless, the deaf subjects were 2.5 times faster at the visual search task.
Visual Recognition as Controlled Search of Complicated Fragments
Authors: Krol V M 
Published: December 2015

We tested the hypothesis that object recognition is an active search of complicated fragments in the visual image. This search is performed in accordance with criteria based on invariant descriptions of an object's perceptual class. The basic strategy is to activate these descriptions during parallel search. ‘Upper’ segments search for appropriate fragments of the picture. ‘Subordinate’ segments are included by request of the ‘upper’ segments. Description segments include three types of records: integral (whole) characteristics of some fragment; characteristics of fragments which are members of this fragment; and characteristics of relations between the fragments. This structure of perceptual description permits parallel analysis of the visual scene by different segments by the ‘autonomy’ principle and permits the use of incomplete sets of segments for recognition by the ‘quorum’ principle. Different ways of forming connections between segment records may be considered as ‘thinking’ components of visual perception. The main points of our model follow from results of our tachistoscopic experiments. We measured thresholds for the recognition of test figures. Different levels of figure complexity were used: parallel lines and strips, geometric figures, schematic faces, textures, etc. It was found that the stages of the recognition process are connected with types of operations described in our model. These results give rise to the possibility that the properties of the neurons involved in visual search might be identified.