bluuebunny/crossref_metadata_2025 huggingface dataset:
Binocular Rivalry in Half-Occluded Regions of Coloured Random-Dot Stereograms
Authors: Suzuki M
Published: December 2015

In normal perception, binocular rivalry does not arise in half-occluded regions. However, when coloured random-dot stereograms (RDSs) were observed, binocular rivalry arose in half-occluded regions. In this study, binocular rivalry in half-occluded regions was studied with coloured RDSs. Coloured RDSs consisted of a central square-shaped region, a background, half-occluded regions, and a probe. The central square-shaped region was coloured white, and was presented in either crossed or uncrossed disparity. The background was coloured yellow. The half-occluded regions were coloured either white, yellow, or blue. The probe was coloured red, and was presented in either of the half-occluded regions. Subjects judged the disappearance of the probe and stereopsis. When the half-occluded regions were coloured the same as the front plane, the probe and stereopsis both disappeared. On the other hand, when the half-occluded regions were coloured the same as the back plane or differently from both planes only the probe disappeared while stereopsis did not disappear. Also, disappearance of the probe decreased more when the half-occluded regions were coloured the same as the back plane, than when the half-occluded regions were coloured differently from both planes. These results suggest that half-occluded regions escape binocular rivalry for several reasons, including ecological validity in 3-D representation, and that half-occluded regions are suppressed interocularly when a static stereogram is observed statically.
Grasping Stereo and Texture Cue Combinations
Authors: Pollick F E , Tittle J S
Published: December 2015

Studies of grasp indicate that the reach-to-grasp movement is essentially preprogrammed and relies heavily on estimates of object geometry provided by vision. Moreover, computational analyses of two-point grasps suggest that the identification of pairs of grasp points requires extensive computation of surface geometry. Thus, one can view subjects' decisions of how to obtain a stable two-point grasp as a good indicator of the perceptuo-motor system's appreciation of surface structure. We probe this perceptuo-motor surface representation by examining grasps to ellipsoidal surfaces defined by the cues of texture and horizontal disparity under independent levels of noise added to both texture and stereo. Subjects viewed the sequential presentation of left and right images on a computer display through liquid-crystal shutter glasses and were instructed to perform either an overhand or underhand grasp to the presented virtual ellipsoid. The virtual ellipsoid was oriented with its long axis in the horizontal plane. Rotation in depth about a vertical axis was varied between trials by a staircase procedure, which obtained the orientation at which overhand and underhand grasps were equally likely as well as the differential threshold. Results showed that the differential thresholds were a few degrees for the zero noise condition and increased with the addition of noise. These results are discussed in terms of theories of cue combination and perception for action.
The Self-Organising Map, a Possible Model of Brain Maps
Authors: Kohonen T
Published: December 2015

We stipulate that the following three categories of dynamic phenomena must be present in a realistic neural-network model: (i) activation; (ii) adaptation; (iii) plasticity control.

In most neural models only activation and adaptation are present. The self-organising map (SOM) algorithm is the only neural-network model that includes all the three phenomena. Its modelling laws include the following partial functions: (1) Some parallel computing mechanism for the specification of a cell in a piece of cell mass whose parametric representation matches or responds best to the afferent input. This cell is called the ‘winner’. (2) Control of some learning factor in the cells in the neighbourhood of the ‘winner’ so that only this neighbourhood is adapted to the current input. By virtue of the ‘neighbourhood learning,’ the SOM forms spatially ordered maps of sensory experiences, which resemble the maps observed in the brain.

The newest version of the SOM is the ASSOM (adaptive-subspace SOM). The adaptive processing units of ASSOM are able to represent signal subspaces, not just templates of the original patterns. A signal subspace is an invariance group; therefore the processing units of ASSOM are able to respond invariantly, eg to moving and transforming patterns, in a similar fashion as the complex cells in the cortex.
Synaesthesia and External ‘Projection’ of Kinesthetic Sensations in Phantom Limb Patients and Normal Individuals
Authors: Ramachandran V S
Published: December 2015

By combining brain imaging (MEG) studies with psychophysical experiments we have shown that, very soon after amputation of an arm in humans, the sensory input from the face begins to activate the original ‘hand area’ of the cortex. Many patients with a phantom arm are unable to ‘move’ their phantom arm. We used a mirror to allow the patient to see the reflection of his normal hand superimposed on the phantom. If he now moved the real arm he not only saw the phantom moving but also experienced vivid kinesthetic sensations in the phantom—a remarkable example of synaesthesia. Finally, we had a normal subject look at his own reflection superimposed on a Halloween mask seen through a half-silvered mirror. If he now made vigorous lip and tongue movements he felt his kinesthetic sensations ‘projected’ on the mask; and his ‘free will’ controlling the dummy's face (it is as though the subject regards it as highly unlikely that his own lip sensations and motor commands should be so perfectly synchronised with the movements of the mask, simply by chance). If the mask was now punched in the eye, the subject registered a strong GSR (galvanic response) demonstrating that his ‘self’ had now temporarily cast off its mortal coil to inhabit the mask.

In our last experiment we had a blindfolded subject repeatedly tapping and stroking the nose of an accomplice who was sitting in front of him. If the experimenter then taps and strokes the subject's nose in perfect synchrony, the subject starts experiencing an absurd lengthening of his nose (the phantom nose). This simple experiment demonstrates the single most important fact about the mechanisms of perception—that they can discern statistical regularities in the world with astonishing rapidity.
Reading with Visual Field Defects
Authors: Trauzettel-Klosinski S
Published: December 2015

The influence of different visual field defects on the reading performance was examined with potential adaptive strategies to improve the reading process in mind. By means of an SLO, the retinal fixation locus (RFL) was determined with the use of single targets and text, and eye movements scanning the text were recorded on video tape. Additionally, eye movements were monitored by an Infrared Limbus Tracker. Visual fields were assessed by the Tübingen Manual and/or automatic perimetry. Normal subjects, and patients with central scotomata, ring scotomata, and hemianopic field defects (HFD) were examined.

The main pathological reading parameters were an increase of saccade frequency and regressions per line, and a decrease of reading speed. In patients with field defects involving the visual field centre, fixation behaviour is significant for regaining reading ability. In absolute central scotoma, the lost foveal function promotes eccentric fixation. The remaining problem is insufficient resolution of the RFL, which can be compensated for by magnification of the text. In patients with insufficient size of their reading visual field, due to HFD and ring scotoma, it is crucial that they learn to use a new RFL despite intact foveolar function.

Preconditions for reading have been found to be: (1) sufficient resolution of the RFL, (2) a reading visual field of a minimum extent, and (3) intact basic oculomotor function. In patients with visual field defects involving the centre, a sensory-motor adaptation process is required: the use of a new RFL as the new centre of the visual field and as the new zero point for eye-movement coordinates.
Colour as Input to Stereopsis
Authors: Baumann C
Published: December 2015

Neural structures carrying information concerning stereopsis belong to the magnocellular sub system of the visual pathway. Regarding the magnocellular system as insensitive to colour, one would expect a high threshold for chromatic stimuli to evoke stereoscopic depth perception. In the present study, a stereogram together with an equiluminant background was generated on a colour monitor. The monitor was calibrated by a tristimulus colorimeter before each experimental session. The chromaticity coordinates of both stereogram and background could be varied in small steps. The author and two naive subjects participated in the experiments. Two patterns of three vertical bars formed the stereogram which was viewed through a stereoscope. With binocular fusion, the spatial arrangement of the bars gave rise to a horizontal, crossed or uncrossed, disparity of 10 min arc for one of the bars. Accordingly, this bar appeared to float either in front of, or behind, the other two, provided the colour difference between the stereo pair and the background was large enough. Under equiluminant conditions, the minimal colour difference necessary to evoke a depth perception exceeded the just noticeable colour difference at the chromaticity coordinates chosen ( x = 0.265; y = 0.499) by a factor of only 3 to 4. In control experiments, the use of an optical system to compensate ocular chromatic aberrations did not measurably alter the results. These findings indicate that colour has an input to stereopsis which is stronger than a purely magnocellular system could provide.
Why Do Some People Take a Long Time to See Complex Random-Dot Stereograms?
Authors: Buckley D , Frisby J P , Aranaz V J , Lipson M M
Published: December 2015

Some observers take a long time to see the appropriate surface shapes depicted in complex random-dot stereograms (RDSs) whereas others report seeing them quickly. We have hypothesised that this may be due in part to some observers being more affected than others by the cue conflicts that are typically present in RDSs, for which disparity is often at odds with accommodation, texture, and outline shape cues.

We report two experiments in which we investigated whether a measure of dominance of texture/outline cues over disparity cues in stereograms of ridges could predict latencies to see RDSs of ‘wedding cakes’ viewed from above. Latencies were measured for correctly reporting the number of layers in the wedding cakes. The ridge cue dominance index was obtained by using amplitude judgements of convex parabolic vertical and horizontal ridge stereograms embodying texture/outline vs disparity cue conflicts (Buckley and Frisby, 1993 Vision Research33 919 – 934). In the first experiment ( N=38) disparity cues in the wedding cakes were depicted with inconsistent dot texture elements, ie the dots signalled flatness as there were no density differences between the cake layers. Observers giving greater weight to texture/outline in the vertical-ridge amplitude task showed significantly longer latencies to the wedding cakes. In a second experiment with different observers ( N=35), 18 were shown wedding cakes with textures consistent with disparity (diamonds drawn with correct perspective and density) and 17 saw the same disparity cues carried by inconsistent textures (diamonds signalling flatness). Large and significant correlations were found between the cue dominance index from vertical ridges and the latencies to wedding cakes depicted with inconsistent textures: observers with higher texture/outline cue dominance showed longer latencies. This result was remarkable given the lack of any readily apparent differences between the consistent and inconsistent textures in the wedding-cake stimuli. Equivalent correlations for wedding cakes depicted with consistent textures were small and nonsignificant. We conclude that individual differences in latencies to complex RDSs can be partly explained by differences in observers' susceptibility to texture/disparity cue conflicts embodied in those RDSs.
Measurements of ‘Von Kries’ Contrast Colours
Authors: Whittle P , Arend L
Published: December 2015

At two previous ECVPs we showed demonstrations and preliminary measurements of contrast colours in a haploscopic display. Colours were presented in different uniform surrounds to the two eyes, superimposed in the binocular field so that they appeared to be in the same surround. Here we report more extensive matching experiments. The principal results are as follows: (1) To a first approximation, in a log MacLeod - Boynton space, perceived colour is determined by the surround-to-colour vector (SCV). The remaining results are second-order deviations from this von Kries scheme. (2) Increment colours are tinged with the hue of the surround, even though that surround hue cannot be seen. This effect of the sign of luminance contrast seems to be just a multiplicative shift: otherwise, increment and decrement data can be superimposed. (3) SCVs for a constant perceived colour shrink and expand slightly with movement along the S-cone axis, suggesting that the transform of S-cone excitation is less compressive than a logarithmic function. (4) SCVs show consistent small rotations, suggesting that L- M and S-( L+ M) axes are not completely independent.
The Preparation of Goal-Directed Movements Requires Selective Visual Attention: Evidence from the Line-Motion Illusion
Authors: Deubel H , Shimojo S , Paprotta I
Published: December 2015

Previous research has demonstrated that visual attention is focused on the movement target, both before saccadic eye movements and before manual reaching, allowing for spatially selective object recognition (Deubel and Schneider, 1996 Vision Research36 1827 – 1837; Deubel, Schneider, and Paprotta, 1996 Perception Supplement, 13 – 19). Here we study the illusory line motion effect (Hikosaka et al, 1993 Vision Research33 1219 – 1240) in a dual-task paradigm to further investigate the coupling of attention and movement target selection.

Subjects were presented a display with two potential movement targets (small circles). When one of the circles flashed, they performed a reaching movement with the unseen hand to the other stimulus; movements were registered with a Polhemus FastTrack system. At a SOA that was varied between 0 and 1000 ms after the movement cue, a line appeared and connected both stimuli. After the reaching movement, subjects indicated the perceived direction of line motion. In a second experiment, saccadic eye movements instead of reaching movements were studied.

The data show that for short SOAs the subjects reported illusory line motion away from the cue location indicating that attention is automatically drawn to the cue. For longer SOAs but well before movement onset the illusory motion effect inverted—evidence for an attention shift to the movement target. The findings were very similar for manual reaching and for saccadic eye movements. The results confirm the hypothesis that the preparation of a goal-directed movement requires the attentional selection of the movement target. We discuss the assumption of a unitary attention mechanism which selects an object for visual processing, and simultaneously provides the information necessary for goal-directed motor action such as saccades, pointing, and grasping.
Advance in Attention Allocation in Visual Search
Authors: Fischer M H , Pollatsek A , Rayner K
Published: December 2015

We investigated the allocation of visuo-spatial attention during dynamic viewing with a dual task. The primary search task (K, H, O, or V among Xs) required sequential left-to-right eye movements. An additional manual detection response was made to a visual probe that appeared early or late after the onset of one critical eye fixation (25 or 170 ms probe delay). The probe appeared either to the left, or directly above, or to the right of the currently fixated character (−10, −5, 0, +5, or +10 characters probe eccentricity).

As predicted from research with single-eye movement tasks, probe detection became faster near the location of the forthcoming eye fixation, indicating an attention shift to that location. Fixation times increased as a consequence of probing, but less so when the probe appeared in the right compared to the left hemifield. Saccade lengths decreased as a result of probing, but remained largest when the probe appeared at +10 characters. These data support the notion of goal-directed attention shifts prior to eye movements in natural viewing.
Categorical Effects in the Perception of Familiar Faces
Authors: Angeli A , Gerbino W
Published: December 2015

Photographs of morphed faces were shown to close friends of portrayed individuals. Three tasks were used: localisation of a morphed target on the continuum between the two original faces, simultaneous same - different discrimination of face pairs separated by a 20% morphing step (AB task), and sequential classification of the same pairs (ABX task). Localisation data were plotted against morph coefficients. Evidence of categorical processing was provided by steeper functions for upright vs upside-down faces.

In the AB task, intermediate faces were discriminated better than faces separated by the same morphing step but closer to one original. This was confirmed in a control experiment where the participants were unfamiliar with portrayed individuals and were unlikely to process our stimuli categorically. The superiority of intermediate faces in the AB task was attributed to a nonlinearity of continua generated by the morphing procedure, and used as a baseline to evaluate ABX classification data. Also in the ABX task, intermediate faces, those straddling the categorical boundary, were classified more accurately than faces located on the same side of the boundary. However, the superiority in classification accuracy was larger than the superiority in discrimination accuracy operationalised by the AB task, as predicted by the categorical perception hypothesis.
Effect of Ambient Illuminant on Surface Colour Constancy
Authors: Kuriki I , Uchikawa K
Published: December 2015

Generally, we are completely enclosed in a real environment, which may act as an entire view-field or adapting field. But in most studies on colour constancy experiments have been made with spatially restricted stimuli. We built a room with gray (N5) walls inside to measure the effect of ambient illuminant on colour constancy. The room illuminant could change its colour from white (D65) to either blue, orange, green, or purple. The observer sat in this main room and adapted to the illuminant for 5 min before the start of the experiment. The observer was shown a smaller room, which had the same variable-colour illuminant, through an aperture (11 deg × 8 deg) in the left side wall. We set the illuminant for each room independently, but in asymmetric illuminant-colour conditions either was set to white. The observer viewed the central part of a colour CRT monitor, placed behind a small aperture (5 deg × 5 deg) in the front wall, and matched its colour appearance to four OSA colour chips in the smaller room.

Under symmetric illuminant conditions, eg blue vs blue, the observers' settings showed a complete match with the physical chromaticities of the colour chips. In asymmetric illuminant conditions, eg white vs blue, matched colours showed systematic deviations from both physical chromaticities and colour constancy. This implies that taking the ambient illuminant as adapting field did not yield perfect colour constancy. We introduce a simple model based on incomplete adaptation to the ambient illuminant and a spatial-interaction mechanism, which accounts for our results.
Spatiotemporal Dynamics of Attention-Induced Distortions and Illusions
Authors: Yoo M H , Schelchshorn J , Chung C S , Sireteanu R
Published: December 2015

Selective attention induces perceptual distortions, ranging from repulsion of objects located near the attended area (Suzuki and Cavanagh, 1994 Investigative Ophthalmology and Visual Science35 2081) to magnification of inattended objects (Tsal and Shalev, 1996 Journal of Experimental Psychology: Human Perception and Performance22 233 – 243). Two hypothetical mechanisms have been postulated: a shift of receptive field positions away from the locus of attention (receptive-field shift hypothesis) or the enlargement of perceived space around the attended location (spatial-enlargement hypothesis). The aim of the present study was to distinguish between these two hypotheses, by investigating the spatial and temporal properties of attention-induced distortions.

Perceptual judgments on Vernier alignment, line tilt, line length, and size of outlined figures were used to measure attention-induced changes in perception. Attention was induced exogenously (by blinking a specific set of dots around the test stimuli) or endogenously (by instructing the subject to selectively attend the dots). After inducing attention, the test stimuli were briefly flashed. A staircase method was used to measure the attentional effect. The experiment was performed with 3 Korean and 3 German subjects.

A vertical line was perceived as repelled from the locus of attention, and a line segment appeared longer when attention was given to its vicinity. In addition, several well-known illusions (eg the Ponzo and the Gibson illusions) were produced by having the subjects merely attend a set of inducing dots. The effects decreased as the distance between the locus of attention or the time between the onset of attention and the stimulus presentation increased. The results imply that the space-enlargement hypothesis provides a better explanation for the attention-induced changes in perception than the receptive-field-shift hypothesis.
Brightness Illusion Induced by Consistency Constraints
Authors: Feher A
Published: December 2015

We present a novel brightness illusion (the ‘Brick Illusion’) that is determined by perceptual interpretation. The image is ambiguous in terms of depth layering, and the strength of the illusion depends on the chosen interpretation. When a certain interpretation is enforced by stereo disparity, and the layering is disambiguated, the strength of the illusion changes according to constraints on the consistency between depth layering, transparency relationships, and surface brightness.

We applied a 2AFC brightness comparison procedure to quantify the strength of the illusion. This procedure allowed us to measure the uncertainty of judgements on relative surface brightness in illusory conditions. The increased uncertainty of our observers among these conditions reflects the multidimensional nature of these judgements.

This paper is linked to the following World Wide Web page: http://zeus.rutgers.edu/∼feher/brick.html . With a Java-enabled browser the reader can change the gray levels of the backgrounds and the disks, the disparity of the disks, and other parameters.
Temporal Correlations in Presentation Order during Learning Affects Human Object Recognition
Authors: Wallis G M , Bülthoff H H
Published: December 2015

The view-based approach to object recognition supposes that objects are stored as a series of associated views. Although representation of these views as combinations of 2-D features allows generalisation to similar views, it remains unclear how very different views might be associated together to allow recognition from any viewpoint. One cue present in the real world other than spatial similarity, is that we usually experience different objects in temporally constrained, coherent order, and not as randomly ordered snapshots. In a series of recent neural-network simulations, Wallis and Baddeley (1997 Neural Computation9 883 – 894) describe how the association of views on the basis of temporal as well as spatial correlations is both theoretically advantageous and biologically plausible. We describe an experiment aimed at testing their hypothesis in human object-recognition learning.

We investigated recognition performance of faces previously presented in sequences. These sequences consisted of five views of five different people's faces, presented in orderly sequence from left to right profile in 45° steps. According to the temporal-association hypothesis, the visual system should associate the images together and represent them as different views of the same person's face, although in truth they are images of different people's faces. In a same/different task, subjects were asked to say whether two faces seen from different viewpoints were views of the same person or not. In accordance with theory, discrimination errors increased for those faces seen earlier in the same sequence as compared with those faces which were not ( p<0.05).
Texture Segmentation and the Familiarity Effect
Authors: Meinecke C
Published: December 2015

Texture segmentation performance is usually defined as being data-driven and bottom - up: visual features of the stimulus—like orientation differences between target and background texture elements—are then evaluated automatically. The question investigated in the experiments reported here is: Are there some hints that not only ‘pure visual features’ determine segmentation performance, but other factors like the familiarity of the stimulus material already exert an influence at these early stages of information processing? The familiarity effect is revealed by better performance when detecting an unfamiliar element embedded in familiar elements (eg an inverted letter ‘N’ among correct ‘N's) compared with the familiar element embedded in unfamiliar elements (see, eg, Frith, 1974 Perception & Psychophysics16 113 – 116).

In a series of experiments, spatial and temporal factors of the stimulus conditions (eg density, jitter, display size, presentation time) have been varied, so as to determine the constraints under which the familiarity effect influences texture-segmentation performance. Results showed that the familiarity of texture elements had a rather strong influence on early visual processes. This influence disappeared only under very restricted display conditions (very short presentation time, very high density). This provides further information on which framing conditions are typical for data-driven early vision processes.
Preventing Local Clustering in Random-Dot Patterns: A New Method to Avoid Perceptual Artifacts
Authors: Puts M J H , Westerhuis M F
Published: December 2015

Patterns consisting of random dots are frequently used in visual science. One disadvantage of using random-dot patterns is the possible clustering of dots. These clusters have a lower spatial frequency than the one derived from dot size. The cluster formation is not present in patterns in which dots are homogeneously distributed, but with these patterns other problems, eg ambiguity in stereograms, occur. A good balance between homogeneous and random distribution has to be found. This problem has often been addressed in half-toning techniques. One of these techniques is force-field random dithering. In this technique each dot has a force field that repels newly placed dots. For generating random patterns, we used a modification of this dithering technique.

This technique is empirically compared with the traditional random-dot patterns. Subjects viewed for 70 ms a 6 deg × 6 deg square consisting of 100 × 100 dots placed randomly or with a force field. Each dot subtended 0.6 min arc. The task was to detect a vertical band of 30 × 100 dots with increased luminance, which could appear either left or right of the midline. The density of the dots was varied between 5% and 25%. The results indicate a significantly larger error rate when using the force-field generated pattern.

We conclude that subjects are using clusters as local cues. These results should warn investigators using random-dot patterns that local clusters could act as serious artifacts.
Orthogonal Optic-Flow Components are Detected Independently: Evidence from Subthreshold Summation
Authors: Meese T S , Avison N P , Kehoe C A , Dalton L E , Hopkin S
Published: December 2015

Spatial summation to threshold for 2-D motion patterns of rotation, expansion, and deformation has recently been shown for human vision [Morrone et al, 1995 Nature (London)376 507 – 509; Harris and Meese, 1996 Perception25 Supplement, 129]. Using a 2IFC subthreshold summation technique, we asked whether superimposed motion patterns of this kind are detected independently. Subjects had to discriminate between random-dot kinematograms constructed from ‘signal + noise’ in one interval and ‘noise alone’ in the other interval. ‘Signal’ comprised one or two components (cmpnt1, cmpnt2) from the set: expansion, contraction, clockwise rotation, anticlockwise rotation, four directions of deformation, and four directions of spiral. In each session, pairs of components were always orthogonal (eg rotation and deformation, but not expansion and spiral). Both temporal intervals (300 ms duration) contained a circular field where dot luminance was softly damped by an annular window, 5 deg in diameter. In each field, 440 randomly positioned dots travelled linearly through 10% of their distances from the origin. In the ‘noise’ interval, all dots had their directions randomised individually, whereas in the ‘signal+noise’ interval, a staircase controlled the percentage of ‘signal’ dots. We measured psychometric functions for detecting cmpnt1, cmpnt2, and the superposition of cmpnt1 and cmpnt2. In most conditions, we found either little or no summation between the two components. In typical cases where summation was found, it was within the boundary of what would be expected from probability summation between two independent detectors. We conclude that in most of the conditions we tested orthogonal optic-flow components are detected independently in human vision.
Interrelation of Tuning Characteristics in Striate Neurons Sensitive to Cross and Corner
Authors: Lazareva N A , Shevelev I A , Sharaev G A , Novikova R V , Tikhomirov A S
Published: December 2015

In the cat striate cortex we have found 56 out of 174 neurons that respond on average by a threefold increase of the responses to cross-like or corner figures flashing in the receptive field in comparison to those to a single light bar of preferred orientation. For 27/56 of these neurons tuning to both cross and corner was investigated. 18/27 neurons responded to both stimuli, while 3/27 cells were sensitive only to cross and 6/27 only to corner. The width, selectivity, and quality of tuning to orientation did not differ on average for stimulation by the bar and figures of both types. The characteristics of tuning to the shape of a figure (the angle between its lines) were about the same for cross and corner. We have found a direct relationship between the orientation tuning width, selectivity and quality for bar, cross, and corner. The relationships between the characteristics of tuning to the shape of a figure were found to be rather more complex. Thus, among 18 cells sensitive to both cross and corner we never met a high selectivity to cross, whereas that was typical for the selectivity to corner. Of the cells sensitive to cross, 35/46 responded to figures with angles of 45° or 90° between the lines, and the rest (11/46) responded to a cross with an angle of 67.5°. The neurons sensitive to corner responded most often to the angle of 67.5° (9/26) and in nearly equal but lower proportion to all other angles. The functional implication of neuronal sensitivity to cross and corner figures is discussed.
Size Distortions: Space-Time Interaction
Authors: Chukova S , Gauzelman V E
Published: December 2015

We used a modified method of constant stimuli to measure spatial interval discrimination thresholds. Horizontal intervals were indicated by a pair of dark vertical lines on a bright background. In each experimental session, thresholds were measured for seven reference stimuli, presented in random order. Reference stimulus separations varied from 9.52 to 16.66 min−1 in increments of 1.95 min−1. The interstimulus interval (ISI) was varied (50, 200, 500, and 1000 ms) between experimental sessions. Stimulus duration was constant at 500 ms.

For all ISI durations, the point of subjective equality (PSE) for small spatial separation references was less than physical equality, the PSE for larger separations was greater, and the PSE was close to physical equality for reference stimuli in the centre of the range. This result is consistent with the modular model [V D Glezer, 1995 Vision and Mind (Mahwah, NJ: Lawrence Erlbaum)]. However, the magnitude of the PSE shifts was affected by the ISI duration: at 50 and 1000 ms, the small spatial intervals were more underestimated and the large ones were more overestimated than at 200 or 500 ms. The discriminability thresholds based on the slopes of the psychometric functions varied inversely with the ISI duration, but at the ISI of 1000 ms increased again. These findings demonstrate that in the sequential mode of presentation the temporal separation can be as important as the spatial separation distribution in determining the PSE. This suggests that these size distortions result more from memory processing than from spatial processing.
Saccade Automation
Authors: Filin V A
Published: December 2015

The comparative analysis of basic saccade characteristics (interval, amplitude, and coefficient of asymmetry) has shown considerable similarities in adults and first-year babies. Distribution curves of intersaccadic intervals under different test conditions all have only one maximum in the range of about 0.4 s, and in all cases the most frequently met intersaccadic intervals (0.1 – 1.0) comprised comparable proportions of all (71.5% – 90.5%).

The concept of saccade automation was formulated on the basis of these data (Filin and Filina, 1989 Zhurnal Vysshei Nervnoi Deyatelnosti29 603 – 607). In our opinion saccade automation is the basic law of saccadic activity, and all diversity of eye-movement activity takes place against the background of saccade automation. Microsaccades and macrosaccades, nystagmus, and rapid eye movements during sleep may be seen as special cases of saccade automation. Saccade automation is conditioned by the activity of brain structures with pacemaker function. Thus saccades are driven at one basic frequency, which is modulated by afferent influences from the retina of vestibular apparatus, proprioreceptors of eye and neck muscles, and efferent signals (forehead and occipital sections of cerebral cortex, cerebellum). At the same time, only one parameter is modulated at one particular moment, for example saccade amplitude in which case interval and orientation are given in a ready form.

Saccade automation has a great functional importance. It increases the scanned area tenfold, it provides compensation of defects in the sensors and the impellent eye apparatus and for the deletion of consecutive images, maintaining the continuity of visual perception. Moving the image on the retina increases the information of the visual channel.
The Impact of 3-D Video Endoscopy on Binocular Perception and Visually Guided Manipulation
Authors: von Pichler C , Fischer S , Radermacher K , Rau G
Published: December 2015

Monocular video endoscopic systems are established in the clinical routine of surgical endoscopy. The introduction of 3-D video systems could improve visualisation of the intracorporal operating site because of the stereoscopic depth information. The goal of our investigations has been to quantify the influence of this visualisation technology on visual perception, on visually controlled endoscopic manipulations, and on the intraoperative performance, including ergonomic and psychophysical aspects. These results are used to define guidelines for improvement and for the integration of such systems into clinical routine so as to achieve optimal support of the medical team.

The comparison of 2-D and 3-D video endoscopic systems showed a general improvement in the performance of endoscopic procedures. However, 30% – 50% of the users had perceptive problems with 3-D endoscopy. To study the problems quantitatively, we compared the case of stereoscopic visualisation with the real situation of direct view onto the specific objects. The users with problems had insufficient binocular depth perception of stereoscopic images for visual discrimination tasks, although their depth perception of real objects was good. Analysis of their eye movements showed significant differences compared with those of users with good binocular depth perception of stereo images. In particular, there were differences in the relation of vergence movements and accommodation. When we compared visually guided manipulations under stereoscopic video sight and direct view, we found the overall manipulative performance of all users to be the same, but the users with problems showed a lower performance in general.

The experimental design and the results are discussed in detail.
Image Segmentation by Local Temporal Phase Differences
Authors: Forte J D , Ross J , Hogben J H
Published: December 2015

Previous research has shown that flickering elements can be grouped on the basis of temporal phase differences. We investigated the spatial and temporal parameters that permit temporal phase segmentation. The stimulus consisted of a regular square lattice of Gaussian spots modulated in luminance against a background of 54 cd m−2. Subjects identified one quadrant which was modulated 180° out of phase to the other quadrants. The modulation threshold was found for temporal frequencies between 4 and 30 Hz. Four Gaussian spot sizes with standard deviations from 0.05 to 0.43 deg were used: lattice spacing was proportional to dot size.

We found that detection of phase differences between large spots failed at about 10 Hz. However, for the smallest dots the task was possible at frequencies of 30 Hz. Furthermore, the elements at the border of the quadrant were necessary and sufficient for maximal sensitivity. Using solid quadrants modulated at 15 Hz, we found that the maximum separation between the flickering quadrants lies between 0.5 to 1.0 deg. The results suggest that there are two systems that use temporal phase for segmentation. The first system operates below 10 Hz, where phase can be consciously followed and integrated over a large area. The second system operates at higher frequencies but only within confined regions of the visual field. Image segmentation for stimuli modulated at high temporal frequencies is not determined by long-range phase synchronisation. We suggest that detection may be mediated by a second-order nonlinearity.
The Arrangement of Corpus Geniculatum Laterale Connections with Oculomotor Structures
Authors: Fedorova K P
Published: December 2015

The primary visual centres are known to be involved in the organisation of oculomotor acts, but the pathways of signal transmission from corpus geniculatum laterale (lateral geniculate nucleus, LGN) to the structures of the oculomotor system remain unknown. The aim of this study on 30 cats was to determine autoradiographically all the possible pathways of visual information transmission from both dorsal and ventral nuclei of the LGN to oculomotor nuclei.

It was found that there were no direct connections of the LGN with the oculomotor nucleus. The connection occurs either through the cortex or through the preoculomotor formations. These pathways are the following: (1) from the dorsal and ventral nuclei of the LGN to the visual pretectum (olivary pretectal nucleus, posterior pretectal nucleus, nucleus of the optic tract) and then to the vegetative part of III nucleus or through nucleus commissurae posterioris, Cajal and Darkschewitsch nuclei to the somatis part of III nucleus and along the medial longitudinal fasciculus to IV nucleus and periabducens region; (2) from the ventral LGN into the deep layers (IV and VI) of the superior colliculus, and then to the Edinger - Westphal nucleus, preoculomotor central gray substance, and VI nucleus; (3) from the dorsal LGN into the deep layers (IV and VI) of the superior colliculus with relay synapses in the parietal cortex and zona insecta; (4) from the dorsal and ventral nuclei of the LGN to nucleus pontis dorsolateralis and paramedianus, being connected with the vermis anterior lobe (V - VII lobes) of cerebellum, and then to nucleus vestibularis inferior and nucleus vestibularis lateralis.
Summation for Stationary and Moving Visual Stimuli in Receptive Fields of Cat Pretectal Neurons
Authors: Dec K , Waleszczyk W J , Harutiunian-Kozak B A
Published: December 2015

Numerous investigations have shown that the cat's pretectal region is involved in various visual habits and in visually guided behaviour. Thus visually driven pretectal neurons should possess summation abilities for integration of incoming sensory information. We investigated responses of 102 neurons in the pretectal region of cats with pretrigeminal brain stem transection using single-unit extracellular recording. Cells were examined with moving and stationary visual stimuli of different sizes. Our purpose was to compare summation characteristics for stationary and moving visual stimuli in the same neuron. Only a small proportion (5%) of pretectal neurons revealed similar summation characteristics for stationary and moving stimuli. The great majority of neurons showed different patterns of summation, depending on the type of the visual stimulus. For example, positive and negative effects of an increase of the stimulus size on the intensity of cellular response were observed. The results suggest that there are several discrete mechanisms subserving integration of sensory information concerning stationary and moving visual stimuli.
Conjunction Search for Stereo and Colour is Serial
Authors: Nakao Y , Mori T
Published: December 2015

We examined whether visual search for a conjunction target defined by stereoscopic disparity and colour is parallel, as indicated by Nakayama and Silverman [1986 Nature (London)320 264 – 265]. The stimuli consisted of arrays of variable size, containing either 15, 25, or 35 elements. The elements were squares and bordered with a frame to ensure stereoscopic fusion. They were clearly distinguishable either in terms of stereoscopic depth or colour. The target was an element with a combination of stereoscopic depth and colour that was unique in each display. Before search, subjects were either instructed to find a target with defined properties, or to find the odd target. When the subjects knew the target properties, there was a significant effect of set size, although overall search times were short. When the subjects were asked to search for the odd target, search times were long and increased as a function of set size. These results suggest that conjunction search for stereo and colour is serial.
Convex Grouping Impedes Detection of Stereoscopic Depth
Authors: Liu Z
Published: December 2015

When two image regions are separated by an occluder, the strength of their perceptual grouping behind the occluder depends in part on the possible smoothness of the hidden contour completions (ie, Gestalt ‘good continuation’). We consider if grouping strength also depends on whether the contour completion is convex or concave.

We hypothesised that the stronger the grouping between two such regions, the harder it is to resolve their relative stereoscopic depth; and employed accordingly an objective method of relative depth discrimination. The stimulus was in stereo. A horizontal bar in the centre of the image occluded two pairs of planar regions parallel with the image plane. One pair assumed a convex (oval) shape behind the occluder, the other pair a concave (hourglass) shape. The regions in one pair had a slight depth difference. The task was to detect which pair was not coplanar.

The convex grouping impeded detection of stereoscopic relative depth (73% vs 86%, F1,10=8.66, p < 0.02). This held even when the convex completion boundaries were less smooth than the concave ones, a result opposite to predictions by Gestalt ‘good continuation’. In a control experiment, the stimulus was viewed with the ‘occluder’ in the background, so grouping was no longer possible. No difference between the two pairs was found.

Our results suggest that convexity, known to play a role in figure/ground segmentation, is also significant in perceptual grouping, and can even win out over ‘good continuation’. We also propose an objective method of depth discrimination to study perceptual grouping in general.
Curvature Biases in Stereoscopic Vision
Authors: Ninio J
Published: December 2015

The reliability of in-depth curvature judgements for linear elements was studied with stereograms that contained two linear targets and a background representing a hemisphere. The targets were arcs facing to the left or to the right, like parentheses. Some formed binocular pairs with (type 1) or without (type 2) in-depth curvature. The others were monocular (type 3). The hemisphere in the background was generated by a random curve (Ninio, 1981 Perception10 403 – 410); it was either concave (hollow) or convex. The arcs had their binocular centre in the plane of the centre of the hemisphere. Each stereogram contained a type 1, and either a type 2 or a type 3 target. Subjects had to judge the hemisphere curvature, then the in-depth curvature of the targets in 32 different stereograms covering all curvature combinations. There were about 15% errors on type 1 targets, and 80% of these occurred when both the hemisphere and the target were convex, the target being perceived as concave, by transparency through the hemisphere. There were also about 15% errors on type 2 targets, but spread among all situations, the trend being to perceive them as slightly concave. The monocular stimuli (type 3) were judged to be frontoparallel in 70% of the cases. Otherwise, there was no directional bias except for monocular arcs on the nasal side, in conjunction with a concave background. Then, the perceived in-depth curvature was in the ‘generic’ direction predicted by associating the monocular arc in one image with a straight vertical segment in the other image.
Orientation Channels in the Peripheral Visual Field
Authors: Snowden R J
Published: December 2015

Peripheral vision has been modelled as a coarser version of foveal vision. Thus visual behaviour elicited by, say, a 2 cycles deg−1 grating imaged foveally would be reproduced in the periphery by a lower spatial frequency (say 1 cycle deg−1). Tuning for orientation is broader at a low than high spatial frequency (Snowden, 1992 Vision Research32 1965 – 1974). Taken together this leads to the surprising prediction that, given a particular spatial frequency, tuning for orientation is narrower for peripheral viewing! In this study it has also been found that orientation tuning broadens with increasing temporal frequency, but the opposite relationship has been reported for peripheral vision (Sharpe and Tolhurst, 1973 Vision Research13 2103 – 2112).

Orientation bandwidths were measured by the method of selective adaptation following the procedures and analysis techniques described by Snowden (1991 Proceedings of the Royal Society of London, Series B246 53 – 59). The results show that orientation bandwidths did indeed narrow as a stimulus was imaged more peripherally, so that its bandwidth in the peripheral retina could be half that of the fovea. However, at a greater eccentricity, bandwidths broadened once more. The results were not influenced by the contrast of the adaptation pattern eliminating visibility as a possible explanation. Increasing temporal frequency broadened orientation bandwidth at all eccentricities.