bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereo Depth Perception Uses First-Order Phase and Second-Order Position Disparities
Authors: Statham A K , Georgeson M A 
Published: December 2015

We examined the nature and variety of cues underlying the use of binocular disparity in depth perception. Stimuli were Gabor patches (Gaussian-windowed sine-wave gratings, 2 cycles deg−1) and horizontal disparities were produced by varying the phase of the carrier grating or the position of the Gaussian envelope (SD=24 min arc), or both. Disparity varied from −180° to +180° of carrier phase (or the positional equivalent) at carrier orientations 0°, 30°, 60° or 90° from vertical. Direction and magnitude of perceived depth were reported in a 2IFC procedure where the comparison interval contained a zero disparity vertical patch. Use of different orientations allowed phase disparity to be distinguished from horizontal position disparity. Two main conditions were tested. (1) In the ‘patch’ condition carrier and envelope disparity varied together, and perceived depth was found to vary monotonically with positional disparity. When carrier disparity was ambivalent (at ±180° phase disparity) or zero (with horizontal orientation) perceived depth followed envelope disparity, showing that 2nd-order (envelope) disparity alone can produce depth. (2) When carrier disparity was varied with the envelope held fixed, perceived depth and discrimination thresholds depended on phase disparity rather than horizontal position disparity, lending support to the phase-based theory of De Angelis, Ohzawa, and Freeman (1995 Perception24 3 – 31). At the larger crossed disparities (−90° to −180°) depth reversed sign, suggesting a role for occlusion cues as well as phase and envelope disparity in stereo depth coding.
Attentional Shifts and the Mislocalisations at the Beginning of a Movement
Authors: Müsseler J , Aschersleben G , Knuf L 
Published: December 2015

When subjects are asked to determine where a fast moving stimulus enters a window, they typically do not localise the stimulus at the edge, but at some later position within that window (Fröhlich effect). We report four experiments aimed at exploring this illusion. An attentional account is tested, on the assumption that the entrance of the stimulus in the window initiates a focus shift towards it. While this shift is under way, the stimulus moves into the window. Because the first phenomenal representation of the stimulus will not be available before the end of the focus shift, the stimulus is perceived at some later position. In experiment 1 we established the Fröhlich effect and showed that its size depends on stimulus parameters such as movement speed and movement direction. In experiment 2 we tested whether the effect changes when the stimuli started from different eccentricities. In experiment 3 we showed that the processing of the moving stimulus benefits from a preceding peripheral cue, and in experiment 4 we showed with a detection task that feature information about the moving stimulus gets lost when it falls into the critical interval of the attention shift. In conclusion the presented attentional account shows that selection mechanisms cannot only be space-based but that they can establish a spatial representation that is also used for perceptual judgement, that is selection mechanisms can be space-establishing as well.
Configuration Saliency Revealed by Dichoptic Masking
Authors: Bonneh Y , Sagi D 
Published: December 2015

We studied suprathreshold spatial integration by testing the saliency of multi Gabor element configurations in dichoptic masking conditions. Dichoptic presentations allows for a competition between spatially overlapping suprathreshold stimuli that involve nonoverlapping receptive fields in the first stage of visual filtering. Different spatial configurations of Gabor patches (sigma=lambda=0.12 deg) were presented to one eye (target) together with a bandpass noise presented to the other eye (mask). After a short rivalry period (128 ms) in which a dominance of one eye was established, a probe (a randomly positioned small rectangle of reduced contrast in the target) was presented for an additional detection period (80 ms). Probe detection performance was measured (2AFC) by finding the mask contrast leading to 75% correct response. We find that textures of randomly oriented patches are more dominant than uniform textures where the effect decreases and even reverses with decreasing of contrast. For suprathreshold (1-D) contours, however, we find that smooth collinear contours are more dominant than ‘jagged’ ones, regardless of contrast. These findings suggest principles underlying an early lateral integration mechanism based on contrast-dependent inhibitory and excitatory connections. This mechanism could be based on iso-orientation surround (2-D) inhibition and collinear (1-D) facilitation, with inhibition being more effective at high contrasts.
Attention to Colour? Detecting and Discriminating Luminance Changes
Authors: Brawn P T , Snowden R J 
Published: December 2015

It is well established that cueing the location of a target stimulus can improve performance on certain visual tasks over ‘uncued’ locations. Here we ask whether cueing the colour of a target can produce similar gains in performance. Subjects viewed a screen on which a large number (16, 32, or 64) of circles were randomly arranged. At random, half were coloured green and half red. After a short period the luminance of one of the circles was altered and the subject's reaction time to this change was measured. Within a block of trials subjects were informed that the target would be one of the red elements, green elements, or could be of either colour. We found that reaction time to detect this change was (1) unaffected by the number of elements on the screen and (2) unaffected by cueing the target colour. The reaction time to discriminate the polarity of this change was (1) unaffected by the number of elements on the screen and (2) faster when the target colour was cued. We therefore demonstrate that cueing the target colour can serve to improve performance under some conditions. We account for these results by suggesting that subjects give greater ‘weight’ to signals from the target colour into a map that guides visual attention—in line with guided search type models (eg Wolfe, 1994 Psychonomic Bulletin and Review1 202 – 238). This cueing effect is therefore only demonstrable in tasks that require ‘focal attention’ (eg Sagi and Julesz, 1985 Perception14 619 – 628).
Selective Visual Attention during Multiple-Process Control
Authors: Fleischer A G 
Published: December 2015

During multiple-task control, eye movements are central for the performance of aimed actions and the development of working strategies. In order to investigate visual and informational workload the behavioural pattern has been analysed. Information presented on a screen has to be visually analysed in order for a decision to be reached on the action to be performed. Normally peripheral vision and the knowledge of the displayed optical structure are used to select the next position of fixation. The resulting scan path is determined by the context and the dynamics of the processes to be controlled. Therefore, the question arises to what extent characteristics of the eye movements are affected by the amount of workload. In order to test this an experimental setup was designed which makes it possible to record eye and head movements simultaneously. From these data the gaze position on the screen could be computed. During the experimental sessions trained subjects were asked to control a complex process simulation by means of cursor movements. This simulation displayed on a high-resolution colour screen consisted of four process units similar to Crossman's water bath paradigm. Temperature and flow rate represent the control variables for each process unit and have to be adjusted to and kept within a certain tolerance range. The visual scan path and all actions on the graphic tablet were recorded continuously during the experimental sessions. An attempt is made here to describe the allocation of attention during multiple-task performance. The results provide evidence that the contextual structure of the task determines the uptake of specific visual information. The amount of visual workload affecting the subject during the control of all four simulated processes is determined by two independent variables: the flow rate (kinetics) and the number of activated processes. On the one hand fixation duration is affected by the kinetics and on the other hand the stability of the activated processes is very sensitive to both independent variables. These effects are due to the limited capacity of the subject to deal with more than one process state within a certain time interval. He or she is forced to divide his or her attention between different processes. There seems to exist only a poor mental representation of the dynamics of several processes running in parallel.
Attention Facilitates Sequential Recruitment in the Perception of Motion Direction
Authors: Isaak M I , Fawcett S L 
Published: December 2015

Sensitivity to the global direction of motion in a random-dot kinematogram (RDK) increases as the number of RDK frames is increased from 2 to about 10. This increase in sensitivity has been termed sequential recruitment and is thought to reflect cooperativity among motion detectors in V5. If attention is not a control state projected from executive to other brain areas, but rather cooperative activity in any brain area as multiple analysers converge on a single stimulus interpretation, then sequential recruitment should be impaired if RDKs are not attended. Motion direction sensitivity in 2-, 3-, 6-, or 10-frame RDKs was assessed under two conditions. In the first, RDKs appeared at central fixation on a random 80% of the trials and 6.5 deg to the right on the remaining 20%. Here, observers would attend the central but not the peripheral RDKs. In the second, RDKs appeared 6.5 deg to the right of fixation on 80% of the trials and centrally on the others. Observers would attend the peripheral but not the central RDKs. In both conditions, RDKs were 8%, 14%, 25%, 45%, or 80% coherent. Similar results emerged for both central and peripheral RDKs: Threshold was higher for 3-frame, but not 2-, 6-, or 10-frame RDKs when RDKs were unattended rather than attended, suggesting that recruitment is slowed in the absence of attention. These results support a network cooperativity view of attention and suggest that attention may influence relatively basic motion perception mechanisms.
Enhancement of Orientation Discrimination with Stimuli in Apparent Motion
Authors: Casco C , Caputo G 
Published: December 2015

Form and motion have been considered to be analysed separately in different streams of the visual system and then recombined at a later stage of computation of forms in motion. Nevertheless, motion analysis is required in visual tasks like breaking of camouflage and this suggests that motion mechanisms respond directly to form attributes. This second possibility was investigated by using stimuli in apparent motion, consisting of two frames in which a target element segregates by an orientation gradient from a texture background of uniformly oriented line elements. Frame-duration thresholds for target-orientation discrimination were measured to assess if they depend on: (1) whether the target is static or moving horizontally (left/right); (2) whether the target is oriented in parallel or orthogonally to the direction of motion; (3) the amount of dynamic noise present in the background texture (dynamic jitter). Thresholds for direction of motion discrimination were also measured as a function of orientation and dynamic jitter. Thresholds for orientation discrimination were lower for a moving than for a static target. Thresholds for orientation discrimination were lower than those for discrimination of motion direction. Thresholds for orientation and direction discriminations were lower when the target was oriented orthogonally to the direction of motion. Dynamic noise interfered only at high levels of background jitter. These results suggest that orientation discrimination occurs before motion-direction discrimination on the basis of a directionally selective mechanism also responding to form attributes. Form discrimination is likely to be enhanced by the motion component carried by contour motion processing similar to that involved in second-order motion which cannot specify direction of motion at its absolute threshold.
Estimation of Visual Performance in Children with and without Binocular Anomalies by Means of a Computerised Coding Test
Authors: Podugolnikova T A , Rozhkova G I , Kondakova I S 
Published: December 2015

Coding tests are regularly used to estimate the capacity for mental work in children entering school and for younger schoolchildren. The task of the child is to fill a special form by putting conventional symbols (codes) under the rows of test objects in accordance with a sample. The results of such testing reflect both visuomotor and intellectual capabilities since, on one hand, a subject has to perform fast eye and hand movements comparing test objects with the sample and drawing codes but, on the other hand, it is not forbidden to memorise codes and to use an optimal strategy for filling the form. In order to make the coding test more suitable for estimating purely visual capabilities, we evolved a computerised version in which codes were changing at each step, thus making their memorisation useless. Such a coding test was used in an examination of 22 children (age 6 – 7 years) with binocular anomalies (strabismus, amblyopia) from special kindergartens and 190 normal children (aged 6 – 9 years) (63 from kindergartens and 127 from school forms 1 – 3). The difference between children with binocular anomalies and normal children of the same age was statistically significant ( p<0.005). The average indices for normal children of different ages differed significantly increasing from 11.8 (at 6 years) to 24.6 (at 9 years) symbols per minute. The effect of learning was also evident: the indexes of 7-year-old children from the first school form were better than in children of the same age from a kindergarten. The correlation between coding indexes and reading rate was positive but rather weak (0.28) in 52 first-form children tested.
Spatial Characteristics of Motion Integration
Authors: Jones E , Harris M G 
Published: December 2015

We asked how the characteristics of a surround could affect the perception of a central component undergoing translational motion. Two adjacent patches of moving dots (100 dots per patch; diameter 2.5 deg) were presented on a VDU screen. A central ‘target’ patch consisted of a combination of signal dots, undergoing left - right translational motion, and noise dots, which moved in random directions at the same speed as the signal dots. To the right of this a ‘probe’ patch contained dots undergoing translational motion. A simple 2IFC task was used to detect the presence of left - right translational motion in the target patch. An adaptive staircase varied the ratio of translating (signal) to noise dots to measure the 79.4% correct point. Preliminary findings indicate that both the directional characteristics of the probe and the degree of separation between the two patches influence sensitivity to the target motion. At large separations, probe characteristics do not influence target sensitivity. As the two patches become closer together, probe motion parallel to the target patch increases sensitivity, whereas orthogonal probe motion decreases target sensitivity. Surprisingly, as the separation between the patches becomes even smaller, sensitivity to the target motion is reduced by a parallel probe and increased by an orthogonal probe. This suggests that spatial motion integration involves facilitation and inhibition between different motion directions, and that these two effects have different spatial characteristics.
Adaptation is Faster after Luminance Decrements than after Luminance Increments, Independently of Test Pulse Polarity
Authors: Poot L , Snippe H P , van Hateren J H 
Published: December 2015

As is well known, dark-adaptation in the human visual system is much slower than recovery from darkness. We show that at high photopic luminances the situation is exactly opposite. In psychophysical experiments on human subjects, we have studied detection thresholds for brief light flashes, at various delays with respect to decrement and increment steps in background luminance. Light adaptation was nearly complete within 100 ms after luminance decrements, but took much longer after luminance increments. In an effort to determine the nature of the threshold dynamics, we have compared sensitivity after equally visible pulses or steps in the adaptation luminance. Flash detectability was initially the same in the pulse and step conditions, but recovered much faster after pulses than after increment steps. This suggests that the initial threshold elevation is caused by the temporal contrast of the background steps and pulses, whereas the residual threshold elevation after an increment step shows an incomplete luminance adaptation. We have substantiated this by manipulating the contrast of a transition between luminances: we found that these contrast manipulations affected only the initial part of the threshold curve, not later stages. Finally, we measured detection thresholds for brief luminance decrements. For these tests with negative polarity, threshold recovery remained significantly faster after decrement than after increment steps in background luminance. Therefore, the asymmetry in adaptation dynamics that we report is indeed related to the step direction of the background luminance, and is not caused by interaction with the test polarity.
Mentally Simulated Reaches for Visual Objects: Effects of Stimulus Orientation and Biomechanical Constraints
Authors: Johnson S H 
Published: December 2015

Recent evidence suggests that mentally simulating an action involves many of the same neuropsychological mechanisms as overt performance. A series of experiments were conducted to evaluate whether representations involved in mentally simulated reaches are constrained by the same biomechanical factors that limit actual movements. Subjects were asked to use either the right or the left hand to acquire a dowel presented visually in one of 24 different orientations within the picture plane. In reaching studies, subjects responded by grasping the target using either an overhand or underhand grip; in the mentally simulated studies, subjects responded by vocally indicating whether they would prefer an overhand or underhand grip if they were to actually grasp the object. Results indicate substantial correspondence between actual and mentally simulated reaching. Grip preferences in both situations are highly correlated, and reflect biomechanical constraints on rotation of the forearm. In both actual and mentally simulated tasks, subjects show clear preferences for grips that minimise perceived awkwardness. In contrast to related work, the time required to perform mentally simulated reaches for visual objects was found not to increase linearly with distance from the resting posture of the response hand. Findings are discussed with respect to the hypothesis that actual and mentally simulated actions involve the same internal representations.
Superior Detection of Audio-Visual Signals over Visual Signals: Are Overt Movements Necessary?
Authors: Doyle M C , Snowden R J 
Published: December 2015

Perrott et al (1990 Perception & Psychophysics48 214 – 226) suggested that the use of auditory information to guide saccadic eye movements may mediate the facilitation of visual search by auditory spatial information. We modified a later paradigm (Perrott et al, 1991 Human Factors33 389 – 400) to re-examine the nature of auditory facilitation for both covert and overt orienting to targets located ±15° from a central fixation point. Participants made a 2AFC response to the orientation of a visual target in each of four conditions: the target was presented (1) alone, or target onset was accompanied by (2) a spatially coincident sound, (3) a centrally located ‘status’ sound, or (4) a change in the fixation point. The auditory stimulus was a 10 Hz click train: the visual target appeared on the left or right of the fixation point at ±15° azimuth and 0° elevation. In experiment 1 foveal vision was necessary to identify the target. However, the stimulus used in subsequent experiments could be accurately identified without overt receptor movement. Subjects were instructed to use eye movements (experiment 2) or to maintain fixation on a central cross throughout the session (experiment 3). Spatial and status sounds had a significant facilitatory effect on target identification both when overt and when covert orienting were employed. This strongly suggests that audio-visual facilitation is not dependent upon overt orienting.
A Quantitative Method to Explore the Assimilation Effects
Authors: Kroon E , Puts M J H , de Weert C M M 
Published: December 2015

The role of central processes in the assimilation effect can easily be shown qualitatively (de Weert and Spillmann, 1995 Vision Research35 1413 – 1419), but it is difficult to measure quantitatively because of the subtlety of the effect. In most experimental designs, the match stimulus differs greatly in appearance from the test stimulus, eg in size or configuration, and because these differences are far more striking than the assimilation effect, matching is difficult. Central processing, eg object segmentation, influences colour spreading. It is this property that we explored with a new approach: a matching task in which the match stimulus has the same properties (eg size and configuration) as the test stimulus. Object segmentation is forced by stereopsis-induced depth. The test stimulus consists of two depth planes, one with black dots and the other with white dots, on a homogeneous gray background. The match stimulus has the same configuration of black and white dots, but now squeezed into a single depth plane. The basic idea behind this stimulus is that assimilation mainly acts on the back plane of a scene (as can be shown experimentally). So, while keeping the appearance of the stimulus the same, subjects can focus on the assimilation effect itself. This new approach allows us to explore more aspects of the assimilation effect and gain insight into the processes involved.