bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
Temporal Integration of Alternately Exposed Monocular Images of a Random-Dot Stereogram
Authors: Pieper W 
Published: December 2015

J R Ewald and O Gross (1906 Pflügers ArchivCXV 514 – 521) reported that monocular half-images presented alternately can be fused to a stereoscopic percept. The situation is like looking through a fence close to the eyes, with picket and gap widths being identical to the interpupillary distance. Though vision is monocular, an observer moving fast enough parallel to the fence will have stereoscopic vision of the scenery behind it. Little is known about the limits of this integrating mechanism. In two experiments, LCD shutter glasses were used to control the viewing conditions of the anaglyphs of a random-dot stereogram. Binocular fusion was supported by a visible binocular fixation mark and a frame around the display. Subjects were eight male and three female students with normal stereoscopic acuity. They were instructed to press a key as long as they could perceive a global figure portrayed in the stereogram (25 min arc disparity). In experiment 1, monocular exposures to the right and the left eye followed each other without pauses. Psychophysical procedures were used to determine the frequency threshold for stereopsis. A breakdown frequency of 2.5 Hz was found, for descending as well as ascending series. Transferred to the concrete example of a fence, the result corresponds to a pace of 0.32 m s−1, with an interocular distance and a fence measure of 63 mm. In experiment 2, alternating monocular exposures of 100 ms duration were separated by variable pauses. Stereopsis disappeared with 8 ms pauses (ascending), and 17 ms pauses (descending). Results may be attributed to integrating mechanisms of binocular cortical cells, rather than to retinal processes (afterimages).
Interruption of Late Visual Processing Causes an Attentional Blink
Authors: Ehrenstein A , Breitmeyer B G , Pritchard K K , Hiscock M , Crisan J 
Published: December 2015

When the task is to detect two letter targets in a stream of non-letter (digit) distractors in rapid serial visual presentation, an attentional blink (AB; ie a deficit in the detection of a second target when it follows the first by approximately 100 – 500 ms) is often found to occur. In a series of four experiments with different numbers of display positions, with or without masking, we show that: (1) the AB, which occurs when all items are presented at the same display location, is reduced when targets and distractors are presented randomly dispersed over 4 or 9 adjacent locations; (2) the AB is reduced with the spatially distributed presentation even when backward masks are used in all possible stimulus locations and when the location of the next item in the sequence is predictable; (3) the AB is not due to either a location-specific forward or backward masking effect occurring at early levels in visual processing. We conclude that the AB is primarily a function of the interruption of late visual processing produced when the item following the first target occurs at the same location. It seems that, in order for the AB to occur, the item following the first target must be presented at the same location as that target so that it can serve both as a distractor and as a mask interrupting or interfering with late visual processing.
Perceptual Salience of Borders between Coloured Regions
Authors: Maloney L T , Yang J 
Published: December 2015

Difference measurement is a little-used but potentially valuable method for studying suprathreshold vision. We used it to investigate the perceptual salience of borders between adjacent uniformly coloured regions. In these experiments, the observer viewed pairs of colours C1, C2 presented simultaneously in two rectangles, sharing a common border, centred on a neutral background. On each temporal 2AFC trial, the observer saw two colour pairs ( C1, C2) and ( C3, C4), and was asked to judge which of the two colour borders was more salient (stronger). In a single condition of the experiment, the colours C1, C2, C3, C4 were drawn from a set of ten colours constrained to lie along a fixed line segment in LMS space extending from the neutral background point (NBP) in a particular direction in LMS colour space. Let D i denote the distance of C i from the NBP in LMS space. A difference measurement model accounts for such data if and only if there is an increasing ‘scale’ f( D) such that ( C1, C2) is judged more salient than ( C3, C4) precisely when f( D2) - f( D1) > f( D4) - f( D3). For each of three observers and eight directions, we found that estimated functions f( D) were concave, resembling power functions with exponents between 0.64 and 1.
Stages of Orientation Coding Assessed by the Tilt Aftereffect
Authors: Anderson R , Georgeson M A 
Published: December 2015

We investigated orientation coding via the spatial-frequency tuning of the tilt aftereffect (TAE). In the single-adaptation condition, subjects adapted to single gratings of 1 or 8 cycles deg−1, 40% contrast, tilted 15° clockwise or anticlockwise from vertical; in two double-adaptation conditions the 1 and 8 cycles deg−1 gratings were superimposed at opposite orientations (‘plaid’ condition) or at the same orientation (‘parallel’ condition). Test gratings of 1, 2, 4, and 8 cycles deg−1, 20% contrast, were presented for 150 ms in an interleaved staircase procedure that measured the TAE by nulling it, hence making a tilted test grating appear vertical. Initial adaptation was for 3 min, topped up for 2 s between test presentations. Results from the single-grating condition indicated broad spatial-frequency tuning of the TAE, since the effect was still strong when tested three octaves away from the adapter. In the parallel condition, the TAEs were around the average of those reported in the single condition. Negligible TAEs were found in the 1+8 cycles deg−1 plaid condition, indicating that opposing adaptations had effectively cancelled each other out. These findings strengthen the suggestion of Olzak and Thomas (1992 Vision Research32 1885 – 1898) that orientation is encoded via an integrative mechanism which pools or sums the outputs of different spatial-frequency channels, and further imply that much of the adaptation responsible for the TAE occurs at this later broad-band stage.
A Method of Identification of Analyser Characteristics That is Free of Probability Summation Effect
Authors: Logvinenko A D 
Published: December 2015

A detection model (originally proposed by Quick) comprising, in a sequence of linear analysers, varphi1, …, varphi n, nonlinear transducer functions, and the Minkowski decision rule, is widely used, especially when it is necessary to take into account the effect of probability summation. However, there is a general belief that the analyser characteristics cannot be determined in detection experiments since there is a trade-off between these characteristics and the decision rule. Here we show how to overcome this problem, ie how to identify the analysers varphi1, …, varphi n despite the probability summation between them. The observer's performance is assumed to be quantitatively defined in terms of an equidetection surface (EDS). Each analyser varphi i is expressed as a weighted sum of linear (coordinate) analysers {phi j}: varphi i=sum j=1 n a ijphi j, so that an identification of the analysers {phi i} is then reduced to evaluating the weight matrix A={ a ij}. It has been proven that A can be uniquely recovered from an ellipsoidal approximation of EDS in the neighbourhood of at least two points. More specifically, the following equation holds true: A−1 DA= H1−1 H2, where D is a diagonal matrix, H1 and H2 are the matrices of the quadratic forms determining the n-dimensional ellipsoids approximating EDS. Thus, the matrix H1−1 H2 known from experiment is a similarity transform of the diagonal matrix, the columns of A being the eigenvectors of H1−1 H2. Hence, any eigensystem routine can be used to derive A from H1−1 H2.
Perceived Velocity in Dynamic Random-Dot Patterns is Influenced by Noise Type
Authors: Owen K A , Raymond J E , Thompson P 
Published: December 2015

Local motion signals can be pooled to detect the direction of coherent motion in random-dot kinematograms (RDKs) having a high proportion of random noise. Noise type does not appear to affect direction discrimination in such displays (Scase et al, 1996 Vision Research36 2579 – 2586). We have observed that RDKs with low coherence yet an obvious global direction appear to move slower than similar RDKs with high coherence. Using judgements of relative speed between RDKs containing different proportions of noise in a 2AFC paradigm we have quantified this effect and sought to determine if the type of noise influences perceived velocity. Levels of coherence in all dot patterns were well above the thresholds for directional judgements. Dots were assigned as ‘Noise vs Signal’ randomly on each frame of the RDK. Noise dots were either of type ‘random position’ or of type ‘random walk’. Position noise dots were randomly repositioned within the area of the display on each frame and had an isotropic distribution of directions and variable speeds. Random-walk dots moved at the same speed on successive frames (their displacement matched to that of the signal dots) but in a randomly chosen direction. The two noise types yielded statistically different results. In RDKs containing random-walk noise, decreasing the coherence of the display (30% signal, 70% noise) reduced perceived velocity (on average to 0.75 of the actual velocity), while increasing the coherence of the display increased perceived velocity until at high coherence levels (80% signal, 20% noise) the perceived velocity approximated the veridical velocity (on average 0.96). The proportion of position noise in a display had no effect on perceived velocity. These basic results are discussed in relation to current models of motion detectors and velocity perception.