bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for a Dual Colour Code for ‘Object Colour’ and ‘Illumination Colour’ in Centre-Surround Configurations with Inhomogeneous Surrounds
Authors: Mausfeld R , Andres J 
Published: December 2015

We provide evidence that the surround-dependent change in appearance of an infield in a centre - surround configuration is not to be understood as an elementary recoding of channels by a simple surround-dependent gain control but in fact mirrors the triggering of a much more complex mechanism for establishing a dual code for ‘object colour’ and ‘illumination colour’. We constructed centre - surround configurations—referred to as Seurat configurations—whose surrounds are given by a random structure of overlapping circles of a fixed diameter. These surrounds have been spatially modulated along the red - green axis only (isoluminance condition), along the luminance axis only (isochromatic condition), and along both axes, while keeping the space average fixed. Unique yellow settings were made for the infield. Our results suggest that the visual system seems to interpret a reduced variance of receptor codes for the surround as an indication of an illuminant that has to be discounted at the location of the infield. Furthermore, for the case of an isoluminant surround with strong spatial red - green modulation only, the unique yellow settings strongly tend towards the ones of an achromatic surround, ie the surround seems to be almost ineffective with respect to a differential gain control. While our data on Seurat configurations with same space-averaged surrounds refute simple notions of functional equivalence, they suggest an interpretation in terms of a triggering of elementary perceptual categories related to ‘object colour’ and ‘illumination colour’.
Successive versus Simultaneous Processes in the Recognition of Visual Patterns
Authors: Soliuñas A , Guriniene O 
Published: December 2015

In earlier experiments with known nonverbal figures that subjects had to memorise, we found that, at the beginning of practice, recognition probability fell with increasing number of elements in a figure. Thus, the recognition process obeyed the principle of successiveness (Guriniene, 1993 Perception22 Supplement, 50 – 51). In order to localise the successiveness at the lower levels of visual information processing, we investigated how the recognition probability for unknown patterns depended on their complexity. Test patterns were nonverbal geometrical figures consisting of four, five, six, seven, or eight vertical and horizontal line-segments. The sequence of each trial was as follows: a sound signal for attention fixation; the test pattern (10 ms); an individually determined interstimulus interval (20 – 125 ms); the masking pattern (200 ms); a pause (0 s, 0.5 s, 1.5 s, 2.5 s, or 4.5 s); three sample patterns. Subjects were asked to identify which one of the three sample patterns presented was the test figure. No dependence of the recognition probability of unknown figures on their complexity was found. We suppose that, in our experimental situation, the feature extraction from the stimulus is a simultaneous process, but the matching of extracted features with information from long-term memory is carried out successively.
Visual Search Processes in Healthy Aging
Authors: Tales A , Troscianko T , Butler S R 
Published: December 2015

It is well established that there are two limiting types of visual search, a pre-attentive parallel and an attention-related serial process. Such different types of processing may depend upon different regions of the visual cortex and such a measurable dissociation of function could provide a useful marker for particular types of cortical pathology, such as that associated with Parkinson's disease, aging, and Alzheimer's disease. For example, recent studies in this laboratory have shown that people with Parkinson's disease have abnormal parallel but normal serial search functions. Plude and Doussard-Roosevelt (1989 Psychology and Aging4 98 – 105) found no difference in parallel processing between older and young adults, but found that older adults performed worse on a conjunction task. The aim of the present experiment was to extend this research and look at the effect of aging on other types of visual search task and to compare these findings to patients with Parkinson's disease and Alzheimer's disease to determine if different patterns of visual function occur. Twenty-five young adults (mean age 32.6 years) and twenty-five older adults (mean age 63.4 years) performed both a conjunction task and a task involving the detection of a target only slightly larger than the distractors (the ‘size’ task). Our hypothesis was that for both types of visual search there would be an increase in search slope in the older adult group compared to the younger adults. Results of a 2-factor (1 between and 1 within) ANOVA performed on the slope values indicate statistically significant main effects of both age ( F=7.661, p<0.008) and search task ( F=25.426, p<0.0001), where in both the conjunction and size task the slope value was significantly greater for the older than for the younger adults. The slope for the size task was significantly greater than that for the conjunction task for both age groups. The results therefore support our hypothesis and further work is in progress to determine the effects of Alzheimer's disease on different types of visual search processing.
Fading of Textured Targets on Textured Background
Authors: Teichmann R , Spillmann L 
Published: December 2015

In 1804 Troxler reported that with strict fixation, a small, low-contrast target presented to the peripheral visual field will tend to fade and ultimately become invisible. Further studies have shown that, in addition to stationary targets, moving and flickering targets will also fade. We studied the role of a texture difference between the target and its background on fading. We found that textured targets fade as quickly as, or even faster than, uniform targets. Typically, the target becomes less salient and after a while disappears in the background. Specifically, we asked whether orientation contrast would influence the time of perceptual disappearance. A grating disk of 2 deg diameter and 0.8 cycle deg−1 spatial frequency was presented binocularly on an equally striped background, 15 deg from the fixation point. The orientation of the target relative to that of the background was varied in steps of 15°, yielding eleven stimuli which were presented in a random order. Each orientation was shown a total of nine times. Luminance, spatial frequency, and contrast were the same for both the target and the background. Time to fading was measured for each target orientation. The results show that orientation contrast strongly affects fading. Time to fading was longest when the grating target and the background were oriented at right angles and decreased symmetrically with decreasing orientation contrast. This result supports the hypothesis that fading is an active neuronal process of long-range lateral interactions.
Does the Gamma Distribution Refer to an Underlying Mechanism in Binocular Rivalry?
Authors: Vallen P H C , Snoeren P R , de Weert Ch M M 
Published: December 2015

Thirty years ago, Levelt (1967 British Journal of Psychology58 143 – 145) fitted the distribution of dominance times in binocular rivalry with the gamma distribution (the distribution function of waiting times for N random events with process speed lambda). Ever since, the gamma distribution has been used to describe the rivalry phase durations, without an explanatory underlying mechanism being given. Although Levelt suggested lambda to be proportional to the stimulus strength (eg contrast, luminance, blur, amount of contour) and N to be ‘successive neural spikes’, this suggestion has never been tested. The purpose of this study was to test whether or not N and lambda represent characteristics of the observer and the stimulus, respectively. To collect the data as accurately as possible, we performed a large number of measurements involving different designs and stimuli. In contrast to previous experiments, collected data were not pooled but were compared within each subject. We tested the hypothesis by collecting time intervals from subjects responding to numerous conditions in which disk - ring stimuli were varied in contrast, blur, or amount of contour in one eye.
Relevant Perceptual Factors in Stereoscopic Displays: Image Disparity, Convergence Distance, and Focus Length
Authors: IJsselsteijn W A , de Ridder H , Hamberg R 
Published: December 2015

Traditionally, visually relevant factors in stereoscopic displays have been investigated within a performance-oriented framework, focusing on the veridicality of depth perception. However, for some applications, most notably in the areas of broadcasting and entertainment, an appreciation-oriented approach seems to be more relevant. Within this framework, we investigated the influence of image disparity, convergence distance, and focus length on the subjective assessment of depth, naturalness of depth, and quality of depth (or preference). Twelve observers with normal or corrected-to-normal vision and good stereopsis viewed a fully randomised presentation of stereoscopic still images that varied systematically in image disparity (six levels of camera base difference: 0, 4, 8, 12, 16, and 24 cm), convergence distance (two levels: 1.30 m and 2.60 m) and focus length (two levels: 10 mm and 20 mm). Each observer was asked to rate, in separate counterbalanced sessions, his/her impression of depth, naturalness of depth, and quality of depth. The results indicate that observers prefer a stereoscopic presentation of images over a monoscopic presentation. A clear optimum was found at 4 cm image disparity for subjective judgments of naturalness and of quality. Depth judgements increased up to an image disparity of 12 cm, a result that is in line with earlier psychophysical literature. There was an effect of focus length only at extreme image disparities. An effect of convergence distance was also found that can be adequately explained by rescaling to match the effective visual disparities. Although there was a strong linear correlation between naturalness and quality (r = 0.96), a small but systematic deviation could be observed. This deviation was best modelled by a linear quality model that incorporates both naturalness and depth.
Summation of Contrast in Perceived Form from Texture
Authors: Laurinen P I , Olzak L A 
Published: December 2015

The relative contrast of two superimposed triangles formed by truncated sinusoidal gratings determines which appears more salient. We have previously reported that the saliency of one triangle is selectively enhanced by superimposing a third grating of similar frequency but different orientation. We now ask how the contrasts of the three gratings combine to determine saliency. Stimuli were two superimposed isosceles triangles, formed by overlaying sharply truncated patches of a sinusoidal grating, one at 1.5 cycles deg−1 tilted +45°, the other at 6 cycles deg−1, tilted −45° from vertical. The sharpest-angle apexes pointed in opposite directions (left or right). Contrasts of the gratings were initially adjusted to yield equal performance when observers chose whether the more salient target pointed left or right following a brief (400 ms) monocular exposure. In each test condition a third grating of vertical orientation (spatial frequency 1.5, 3, or 6 cycles deg−1) was added to the entire stimulus at one of six contrast levels ranging from near threshold to 10 × threshold. The point of equal saliency was re-determined from psychometric functions by varying the contrast of one triangle in a 2AFC staircase procedure. The saliency of each triangle was enhanced when the third grating was matched in frequency, but no effect occurred when the third grating differed by an octave (eg was 3 cycles deg−1). Beyond some threshold value of the third grating contrast, the contrast needed to reinstate equal salience was found to be inversely proportional to the contrast of the third grating. Our results are in agreement with the characteristics of higher-level mechanisms that mediate spatial-grain and/or pattern contrast discrimination, and suggest that form-from-texture mechanisms sum component contrasts linearly over a wide range of orientations within a narrow frequency band.
Eye Movements in Judgements of Facial Expressions
Authors: Osada Y , Nagasaka Y , Yamazaki R 
Published: December 2015

We recorded eye movements by the method of corneal reflection while ten subjects viewed schematic faces drawn by lines. Each subject viewed different emotional faces: happy, angry, sad, disgusted, interested, frightened, and surprised. We measured the subject's judgements in terms of percentage ‘correct’ and reaction time. Schematic faces were composed of the face outline contours and of the brow, eyes, nose, and mouth which could all be modified to produce particular expressions. By masking parts of the face, we examined which features would have the greatest effects on judgements of emotion. Subjects always gave a saccade to the eyes and fixated even when the eyes were not important for the judgement. They also gave a saccade to the centre of the face and fixated it even when only the mouth was presented. The presentation of only the brow decreased the correct rate on the expression of ‘surprise’ but played an important role in the ‘sad’ judgement. The ‘angry’ judgement depended significantly on the brow and mouth. The eyes contributed greatly to the ‘disgusted’ judgement. These results suggest that the judgement of facial expressions of emotion can be strongly affected by each part of the schematic face. The concentration of saccades on the centre of the face suggests that the ‘configuration balance’ of the face is also likely to be important.
On the Nature of the Gated Colour Opponency in the On-Units of the Frog Retina: Electrophysiological Study and Model
Authors: Maximova E M , Maximov V V , Orlov O Y 
Published: December 2015

Ganglion cells of the ON-type in the frog retina produce colour-dependent responses differing in temporal patterns (short bursts to excitation of red-sensitive cones as opposed to prolonged discharges if blue-sensitive ‘green rods’ are excited). Their gated colour opponency (Kicliter et al, 1981 Brain Research210 103 – 113; Maximov et al, 1985 Vision Research25 1037 – 1049) becomes apparent from the OFF-responses in conditions when the test stimuli are superimposed on a background of another colour. So, when blue glass is introduced in the light beam (decreasing the excitation mainly of red-sensitive cones), an OFF-response is observed, much like the response to the onset of blue light. It has been suggested that opponency in ON-cells is asymmetric, ie that the red signal reaches the blue channel with reversed sign, but not vice versa. A single-unit-recording study revealed the dependence of ON-cell responses both on the colour of stimuli presented in the centre of the receptive field and on the steady illumination of its surround. Surround illumination was found to favour OFF-responses in ON-units. In some cases even the cessation of blue light elicited an OFF-response with a discharge pattern resembling that of the onset of red light. In these cases an ON-response to yellow glass could also be obtained. These observations prove some degree of symmetry in the opponency of the red and blue channels. It is suggested that feedback from horizontal cells onto photoreceptor terminals is involved in the gated colour opponency. A circuit model that reproduces the observed phenomena is presented.
Search Asymmetries in the Detection of Shape Orientation: The Role of Implicit Axes of Elongation and Symmetry
Authors: Boutsen L , Marendaz C 
Published: December 2015

Two-dimensional (2-D) shape identification is sometimes described in terms of access to structural descriptions based on the extraction of principal axes of elongation and symmetry. In four experiments we examined the effects of implicit axes of elongation and symmetry on visual search for shape orientation, on the basis of previous observations of search asymmetries in the detection of the orientation of line segments. We found search asymmetries in the detection of vertical versus oblique line segments and in 2-D shapes, studied earlier by Quinlan and Humphreys (1993 Perception22 1343 – 1364): search times for a vertical target among oblique distractors (rotated 18° from the vertical) are higher than those for an oblique target among vertical distractors. We found that the search asymmetry in the detection of shape orientation is larger when the shape contains an unambiguous axis of elongation or symmetry. Search asymmetries disappear when the principal axis of the shape is oriented horizontally, or when the shape contains no unambiguous axis of elongation or symmetry. Overall search times tend to decrease when the axis of elongation is aligned with an axis of symmetry. These results suggest that the detection of implicit axes plays a role in the perception of object shape and orientation.
Conflicts with Extraretinal and Monocular Cues Cause the Small Range of the Induced Effect
Authors: Banks M S , Backus B T 
Published: December 2015

A vertical magnifier before one eye causes the induced effect: an apparent rotation of frontal surfaces toward that eye. The rotation required to restore apparent frontoparallelism grows linearly up to ∼4% magnification, but plateaus at 8%. We examined the cause of the plateau. Horizontal disparities (quantified by horizontal size ratios, HSRs) are ambiguous indicators of surface slant. Various retinal and nonretinal signals can allow veridical slant estimation from HSR, sensed eye position, vertical disparities (vertical size ratios, VSRs), and monocular cues. Vertical or horizontal magnification of one eye's image alters the natural relationships among HSR, VSR, eye position, and monocular cues. We argue that the induced-effect plateau is caused by conflicts between these means of estimating slant. A plateau is not observed in the geometric effect because some of the conflicts do not occur with horizontal magnification. Two experiments were designed to test this hypothesis. When strong monocular cues were present, plateaux occurred at ∼8% magnification in the induced, but not the geometric effect. When monocular slant cues were made useless, induced-effect plateaux were abolished. Even with strong monocular cues present, plateaux in the induced effect were eliminated when eye position was consistent with the vertical magnification in the retinal images. The smaller range of the induced effect can only be understood from consideration of all the signals involved in slant estimation.
Discrimination between Plaids: Do Oriented Filters Combine Dichoptically?
Authors: Olzak L A , Wong R L 
Published: December 2015

Two oblique gratings combine perceptually to form a chequerboard appearance under monoptic presentation but not under dichoptic presentation (Georgeson and Meese, 1996 Perception25 Supplement, 121), suggesting an early combination process. Combining processes that operate over orthogonal orientations are also observed in complex pattern discrimination tasks (Olzak and Thomas, 1991 Vision Research31 1885 – 1898). We ask here whether the interactions observed in discrimination tasks occur before or beyond the site of binocular interaction. Observers discriminated between two patterns that differed slightly in their spatial-frequency content. On each trial, one of the two patterns was presented. Observers judged which stimulus had been presented on a 1 – 6 confidence scale. In control conditions, the stimuli were single sinusoidal gratings near 3 cycles deg−1, and were always presented monoptically. In test conditions, a second component was added to the first in each stimulus. The second component was either presented to the same eye as the first component (monoptic presentation), or to the other eye (dichoptic presentation). The second component was either a mask of exactly 3 cycles deg−1, or varied to give a second cue to discrimination. Second cues either varied with the first (both components lower frequency or both higher) or varied in opposite sign (high with low). Rivalry was eliminated by using low contrast (10 × threshold) and small (1.2 deg) patterns. Our results suggest that the combination processes we observe occur beyond the site of binocular combination and differ from those mediating the percept.
Centre-Surround Tuning of Orientation Detectors in Human Vision
Authors: Ringach D L , Shapley R 
Published: December 2015

We present a new psychophysical method to study the tuning of orientation detectors in the human visual system. The stimulus consists of a sequence of sinusoidal gratings of random orientations and spatial phases (but of fixed spatial frequency) shown at a high presentation rate (30 Hz) in 60 s long trials. The gratings are seen through a circular aperture. The subject's task is to report, as fast as possible, by pressing a key, when the presence of a horizontal grating is seen embedded in the stimulus sequence. The data are analysed by calculating the distribution of orientations present in the stimulus sequence at different times [before] the key was pressed. Similar experiments can be done by asking the subject to detect vertical and oblique orientations. In these experiments we used 100% contrast, a 3 deg diameter circular aperture, and spatial frequencies ranging from 1 to 4 cycles deg−1. The resulting orientation-tuning profiles have a ‘centre—surround’ (or Mexican hat) shape in the orientation domain. These findings are consistent with the idea of fast ‘lateral inhibition’ between orientation detectors. The centre—surround profiles may explain systematic errors in visual angle judgments, such as the perceptual expansion of acute angles and the contraction of obtuse angles, the tilt aftereffect, and the effects observed in the Zöllner, Hering, Ponzo, and Poggendorff illusions.
Effects of Aging on Photoreceptors and Implications for Visual Performance
Authors: Leibovic K N , Bandarchi J 
Published: December 2015

Visual performance depends in the initial stages on the properties of retinal photoreceptors. In this context we consider the effects of rod outer segment (OS) renewal and OS response gradient on performance. The OS renews itself by forming new membrane near the cilium, at the base of the OS. This membrane then advances towards the tip where it is shed and phagocytosed in the pigment epithelium. Thus the OS is older at the tip than the base, and it has been proposed that it is due to this aging that the observed light responses are smaller and slower at the tip than at the base. We have tested this hypothesis by exposing Xenopus laevis in a controlled manner to altered temperature and lighting conditions which are known either to slow down or to accelerate OS renewal. We have recorded the light responses of the OS base and tip and found that they are, indeed, correlated with the age differences. In addition to OS membrane age we have also investigated the effects of animal age on the response gradient along the OS. Here we found that during development the response differences decrease and then stabilise at maturity. Concurrently with the decrease of the gradient the response kinetics are slowed down. There is thus a changing trade-off between response gradient and kinetics up to maturity in this animal. These results have important implications for visual performance. Visual reaction times depend on photoreceptor kinetics; and since photons can be absorbed anywhere along the OS, the response gradient, especially at low light levels, directly affects the reliability of detecting stimulus intensity. We conclude that visual performance in Xenopus laevis is related to the rates of OS renewal and the resulting response gradient in an age-dependent manner.