bluuebunny/crossref_metadata_2025 huggingface dataset:
The Misperception of the Direction of a Feature Added on a Moving Line is Eliminated with Static Cues
Authors: Dufour A , Castet E
Published: December 2015

It has been reported earlier that a feature (a gap or a dot) added on an oblique line which is translating vertically behind a horizontal rectangular aperture (we call this the basic display), appears to slide along that line while the perceived direction of the line is horizontal. Castet and Wuerger observed that, when the aperture is a visible circular outline, the perceived ‘sliding’ of the dot is significantly reduced compared to the conditions where the aperture is invisible. They suggested that the misperceived direction of the dot in the invisible-aperture condition might be due to a lack of static cues. To investigate this hypothesis further we ran a similar experiment in which the aperture was a rectangle. Subjects had to report with an adjustable arrow the direction of the dot added on the line. Results showed that the sliding effect completely disappeared when the rectangular aperture was visible (white outline) compared to the condition where the aperture was invisible. We hypothesised that better performance is obtained when the outlined aperture is rectangular rather than circular because of additional vertical cues. Therefore, in a second experiment using the basic display mentioned above, we tested how a single static dot affects the ‘sliding’ effect. The static dot was either vertically aligned or not, with the dot placed on the moving line. Results showed that the sliding effect was significantly reduced but not eliminated when the static dot was aligned vertically with the moving dot, compared to the conditions where the static dot was not aligned vertically with the moving dot (or where there was no static dot at all). This suggests that static features providing alignment information are optimal for eliminating the misperception of the direction of a moving feature.
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.
Neural Image Enhancement Allows Honeybees to See at Night
Authors: Warrant E J , Porombka T , Kirchner W H
Published: December 2015

The optical design of most insect apposition compound eyes should restrict activity to daylight because at night the tiny lenses of the isolated ommatidia cannot collect sufficient light. However, several bee species have adopted nocturnal activity, taking advantage of the benefits of night foraging. By measuring behavioural visual performance in honeybees, we show that insects can possess better spatial resolution in dim light than the optics and physiology of their apposition eyes suggest, implying the presence of higher neural mechanisms which enhance vision at night. Theoretical calculations reveal that honeybees improve light capture at night by neurally summing photons in space and time. Even though summation compromises both spatial and temporal resolution, the improved photon capture enhances vision sufficiently for bees to discriminate coarse images in moonlight. This explains how bees and many other insects can adopt a nocturnal life style despite having an eye design typical of a day-active insect.
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).
Anisotropic Temporal Integration in the Perception of Stereoscopic Corrugations
Authors: Hegarty M R , Hibbard P B , Bradshaw M F , De Bruyn B , Parton A D
Published: December 2015

Disparity sensitivity for horizontal depth corrugations increases with exposure duration for presentations of up to 1 s (Tyler, 1990 Vision Research30 1877 – 1895). To extend the work of Parton et al (1996 Perception25 67) we investigated whether differences existed in the effects of exposure for corrugations at different orientations. Disparity thresholds were measured for horizontal, vertical, and diagonal gratings with spatial frequencies ranging between 0.1 cycle deg−1 and 0.8 cycle deg−1, as a function of stimulus duration. Stimuli were presented for exposures of between 50 ms and 32 s, and were followed by a random disparity mask, which served the important function of disrupting further processing of stimulus disparity. Thresholds were greatest for vertical gratings. This effect was particularly pronounced for the lowest frequencies. In all conditions, disparity sensitivity improved as exposure duration increased, and continued to do so for all durations tested. For vertical and diagonal gratings, log - log plots of threshold against time showed a linear relationship with a slope of −1 up to 1.0 s, after which time improvements in sensitivity reduced. Horizontal gratings showed a similar relationship, but with thresholds ceasing to decrease significantly after 0.5 s. Temporal integration limits differ with surface orientation, and represent another important difference in our ability to detect and encode depth in stereoscopic surfaces.
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.
Differences in Processing Time for Stereoscopic Inclination and Slant
Authors: Hibbard P B , Bradshaw M F , Gillam B
Published: December 2015

Howard and Kaneko (1994 Vision Research34 2505 – 2517) suggested that stereoscopic slant and inclination may be encoded on the basis of relative expansion and shear, respectively. We investigated the perception of surfaces with diagonal axes of tilt, having components of both inclination and slant. Latencies for the perceptual resolution of slant can be several times those for inclination (Gillam et al, 1988 Journal of Experimental Psychology14 163 – 175). Using a forced choice methodology, we measured the time required to discriminate surfaces with horizontal, vertical, and diagonal axes. Subjects were presented with random-dot stereograms of planar surfaces, with or without a visual reference. Stimuli were followed by a random-disparity mask. In the first experiment, subjects discriminated the direction of slant or inclination of surfaces rotated in depth by 45° from frontoparallel. A staircase procedure was used to find the shortest presentation time for which surfaces could be correctly discriminated. With a visual reference, both surface types could be discriminated with brief presentations. Without a reference, mean thresholds were 300 ms for inclined surfaces, and 2.5 s for slanted surfaces. In a second experiment, temporal thresholds were measured for surfaces with diagonal axes. In one condition, subjects discriminated between surfaces with equal inclination, but opposite slant. In the second condition, surfaces had equal slant, but opposite inclination. Surfaces differing in inclination could be discriminated with shorter presentations than surfaces differing in slant. These results support the notion that surfaces are encoded in terms of components of inclination and slant.
Detection of a Point-Light Walker within a Mask: Effect of Display Orientation
Authors: Pavlova M A , Sokolov A N
Published: December 2015

How, if at all, does display orientation affect the extraction of a known structure in biological motion? A computer-generated 11-point-light walker was simultaneously masked by 66 dots that corresponded to scrambled triads of points on his limbs. At each of 5 randomly presented orientations between upright and inverted (0°, 45°, 90°, 135°, 180°), observers saw a sequence of 210 displays, half of which comprised a walker within a mask, while the rest presented only a 77-dot mask. In a confidence-rating procedure, they had to judge whether a walker was present. A sample of the target was demonstrated before each experimental sequence. ROC analyses showed that detectability decreased with changing orientation: performance began to deteriorate already at 45°. For orientations of 90°, 135°, and 180°, the ROC curves were situated close to one another. Nevertheless, given the complexity of the mask and the brief viewing period (1 s), with inversion (180°) detectability was still surprisingly high (cf Bertenthal and Pinto, 1994 Psychological Science5 221 – 225). Comparison with data on spontaneous recognition of biological motion (Pavlova, 1996 Perception25 Supplement, 6) suggests that display orientation affects bottom - up visual event processing more strongly than top - down. We consider the relative power and interrelation of processing constraints (such as axis of symmetry, dynamical constraints) in the perception of invariant structure from biological motion.
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.
Can Illusory Figures Be Transparent and Opaque at the Same Time?
Authors: Purghé F
Published: December 2015

A simple and convincing way of explaining illusory figures is based upon the idea that the visual system would infer the presence of an occluding object when the inducing pattern shows features, such as indentations or interruptions, that can be logically explained as due to an occlusion. This kind of explanation implies (a) that an illusory figure should be prevented from occurring if there is no logical need for it, and (b) that the illusory figure must be opaque to be effective as an occluding object. It can be shown, however, that illusory figures can emerge even when there is contrary evidence to occlusion. A special kind of stereoscopic Kanizsa-like pattern superimposed onto a picture (an Escher engraving) is capable of inducing clear illusory figures (two rectangles). In this pattern, the illusory figures seem to be transparent with respect to the picture on the background, which remains fully visible through them, but act as opaque surfaces with respect to the inducers. The inducers are parts of a Necker cube which can be clearly seen only when its fragments induce the illusory rectangles, but disappears if the same fragments, being only outlined, are not able to induce them. If this outcome can be regarded as a demonstration that the Necker cube can be seen as an amodally completed object only when it virtually completes itself ‘behind’ the illusory rectangles, one would have to conclude that the same illusory surfaces can be transparent and opaque at the same time. This paradoxical result seems to challenge any interpretation of illusory figures as being due to an intelligent solution to a cognitive problem.
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.
Testing the Hypothesis of Labelled Detectors
Authors: Cogan A I
Published: December 2015

The hypothesis of labelled detectors (or ‘lines’) is the present-day version of the basic Müller - Helmholtz doctrine. Müller's dictum of specific energy of nerves stated: “the same internal cause excites (…) in each sense the sensation peculiar to it”. Helmholtz made ‘the cause’ external to the body and postulated that all knowledge about the world thus comes through the senses. The key word is specificity. The strong version of the hypothesis must treat detection - identification as a single task: a stimulus would be identified whenever it is detected. The weak version requires only that we identify a specific mechanism by which both detection and identification are achieved, even though the latter may require additional processing. In the general case, the strong version (with its ludicrous ‘grandmother cell’ as the neural substrate) finds little support. Detection and recognition of complex shapes (letters, faces, etc) aside, even discrimination between simple increments and decrements of luminance is difficult to attribute directly to a specific mechanism (in this case, the activity in either ON or OFF systems, respectively). This is demonstrated by experiment 1 reported here. However, perception of relative depth seems to conform to the strong version of the hypothesis, as experiment 2, also reported here, indicates. Thus, at least some specific neural mechanisms (in this case, probably the crossed and uncrossed disparity detectors) may be indeed linked directly to perception.
Stereoscopic Vision Deficiency in Auditory-Deprived Children
Authors: Golubkov M G , Krasnoperova N A
Published: December 2015

There is a widespread opinion that in deaf persons, on average, the visual system should be more highly developed than in people with normal hearing. However, one could also argue that normally the auditory system promotes the development and refinement of visual spatial mechanisms since localisation of many objects in the environment can be accomplished by visual and auditory systems simultaneously and, hence, can be done faster and more reliably. Because such supporting interactions in auditory-deprived children are absent or are weaker, one could expect slower or imperfect development of their spatial vision. We tried to test this hypothesis with the aid of a special test software (CLASS) allowing generation of random-dot stereograms (RDSs) in anaglyphic form (red - blue images). The varying parameters of RDSs were dot sizes (1 – 8 pixels) and brightness contrast of the blue image. The judgement about a subject's stereo vision was based on the presence of a stereo effect per se and on the brightness contrast threshold for the recognition of 3-D objects. The group of auditory-deprived children consisted of 70 subjects aged 3 – 9 years, the whole control group included 131 schoolchildren aged 7 – 9 years, but 87 subjects were only tested for the presence of a stereo-effect. The monocular visual acuity of all children was normal or corrected-to-normal. The results of testing by CLASS revealed significant visual deficiencies in auditory-deprived children: 10 (14%) were found to be stereo-blind, and 5 (7%) had markedly increased thresholds. In the control group, the percentage of stereo anomalies corresponded to the typical value of 2% – 4%: stereo-blindness was found in only 2 of all 131 children (the cases of strabismus and ptosis) and elevated thresholds were found in 2 children (out of 44).
Spatial and Temporal Integration of Biological Motion
Authors: Neri P , Morrone M C , Burr D C
Published: December 2015

We studied spatiotemporal integration of biological motion using a summation technique. Subjects had to identify coherent from incoherent motion of a synthetic walker against a background of noise, where incoherence is produced by moving the upper and lower body in opposite directions. Performance (defined as the maximum added noise for reliable discrimination) increased steeply with exposure duration, up to very long intervals, in the order of seconds, far longer than for simple motion targets (complete by about 100 ms). Varying the speed of the walker suggested that the limiting factor for performance is the total information about the stimulus (accrued over seconds), rather than stimulus duration per se. Sampling the joints during the motion sequence (with a ‘limited lifetime’ paradigm) revealed very strong spatial summation. Sensitivity increased with the cube of the spatial information content. The spatial and temporal summation seemed to be independent of each other.
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.
Perception of Geometrical Figures in Persons with Damaged Temporal Lobes
Authors: Lukauskiene R , Bertulis A , Busauskiene I , Mickiene B
Published: December 2015

Persons with damaged temporal lobes were tested with computerised tests for size and form discrimination developed by A Bulatov and A Bertulis (1994 Perception23 Supplement, 25). 48 persons with damaged right and 54 persons with damaged left temporal lobe were tested. 8 persons showed hemineglect of the right visual field and 10 persons hemineglect of the left visual field. Posner (1987 Neuropsychologia25 135) stated that persons with unilateral spatial neglect had a specific inability to disengage their attention from a given object in order to reallocate it to another object positioned to its left or right. In our studies we determined whether size discrimination abnormalities also occur in the neglected side, opposite to the damaged temporal lobe. We estimated the accuracy with which subjects judged the height of two squares of different colours. Two squares with sizes varying from 0.2 to 3.0 deg were generated on the right and left side of the monitor. Subjects viewed the patterns binocularly at a distance of 1 m and adjusted the size of the square on the left to make its height equal to that on the right. The error of the setting was recorded. Persons with hemineglect of the visual field were unable to concentrate their attention at two figures located on both sides of the monitor so they were unable to make the comparison. Persons with right and left temporal lobe damage without hemineglect of the visual field judged the geometrical figures better than those with hemineglect but worse than controls. Persons with damaged left temporal lobe judged figures less well than persons with damaged right temporal lobe.
Computer Interactive System for Diagnosis, Testing, and Rehabilitation of Visual Perception Disorders
Authors: Ruseckaite R , Raskinis G , Lukauskiene R
Published: December 2015

According to the data of A Christianson (1992 Acta Neurologica Scandinavica86 545 – 554) the testing of half of the visual field is useful when testing patients who suffer from visual perception disorders (VPDs). With this in mind, a new computer interactive system was developed for diagnosis, testing, and rehabilitation of VPDs. Our computer interactive system was composed of several subsystems: test procedure, test records database, and machine learning algorithm. The interactive test procedure was controlled by several parameters. Results (individual tests, averages) were presented in stereo 3-D form. Individual test records were preserved and formed a database. This database was used by the machine learning algorithm (A Raskinis, 1980, FTEPI Technical Report) to create rules for VPD prediction. Medical computer-aided learning experiments with persons with some kind of VPD have been carried out in the Neurosurgical Centre of Kaunas Academic Clinics with the use of a PC (IBM AT 486). So far we have tested 52 persons with damaged right and left temporal lobes. Our objectives were: (1) to diagnose various kinds of VPD; (2) to train and rehabilitate persons with various kinds of VPD; (3) to collect and analyse data on persons who can be treated and trained; and (4) to develop efficient helping measures and new skills from the effects of intensive training.
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.
Central Visual Persistence as Measured by the Redundant Target Effect
Authors: Marzi C A , Nitro G , Prior M
Published: December 2015

We measured the duration of central visual persistence by testing normal subjects for the redundant target effect (RTE), ie the speeding up of reaction time to redundant visual stimuli in comparison to similar single stimuli. Brief LED-generated flashes were presented to normal subjects either singly or in a pair at peripheral visual field locations (5 or 30 deg along the horizontal meridian). Stimulus pairs could appear either in the same hemifield at different locations or in opposite hemifields with a stimulus onset asynchrony (SOA) ranging between 0 and 100 ms. The subject's task was to press a key as soon as possible following the appearance of either a single stimulus or of the first stimulus in a pair. We found a robust and consistent overall RTE with double stimuli yielding faster RTs than single stimuli for both intrafield and interfield presentations. The effect decreased significantly from 0 ms to 40 ms SOA and at longer SOAs the speed of response to stimulus pairs was indistinguishable from that to a single stimulus. We believe that the longest SOA compatible with a reliable RTE (40 ms) reflects the duration of central persistence. Evoked-potential evidence gathered in our laboratory suggests that the locus of such persistence may be the extrastriate visual cortex.
The Effect of Pedestal Contrast on Choice Reaction Times to Contrast Increments
Authors: Tiippana K M , Paramei G V , Alshuth E , Cavonius C R
Published: December 2015

Two-alternative forced-choice reaction times (RTs) were measured and psychometric functions constructed for ten contrast increments at seven pedestal contrasts ranging from 0% to 4.8%. Two sine gratings at 2 cycles deg−1 differing only in contrast were presented on a computer screen, and the subject's task was to indicate as quickly as possible whether the stimulus with higher contrast appeared to the left or to the right of a fixation point. There were 100 trials per stimulus pair from which the percentage of correct responses and the median correct RTs were calculated. As the contrast increment increased, the percentage of correct responses increased and RTs decreased reaching a minimum with large increments. However, RTs continued to decrease even when performance reached 100% correct. Contrast increment thresholds calculated at 82% correct level formed a classical dipper-shaped function when plotted as a function of pedestal contrast. Response variability, reflected in standard errors of increment thresholds, was greater at high pedestal contrasts. When RTs corresponding to threshold increments were interpolated and plotted against pedestal contrast, the functions were also dipper-shaped. Discriminative RTs were on average faster at low and slower at high pedestal contrasts compared to detection. These findings show that equalising the percentage of correct responses did not equalise RTs, and that processing time increased with pedestal contrast. The increase of both increment thresholds and RTs with pedestal contrast may be due to an increase in signal-dependent noise which increases response variability and slows down the decision process.
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.
Slight Defects of Basic Visual Functions as a Risk Factor for Mental Development in Infants
Authors: Nevskaya A A , Bondarko V M , Leushina L I , Turkina N V
Published: December 2015

The development of the representation of the visual world in infants was investigated and age norms were established for such operations as prediction of direct movement, search for hidden objects, and discrimination and recognition of the form, size, colour, and spatial position of objects. Simultaneously, basic visual functions were assessed: binocular fixation, eye movements, visual fields, and visual acuity. More than 700 infants aged 4 – 14 months were tested. About 25% of practically healthy infants showed slight defects in some basic visual functions, constituting a ‘risk group’. Infants of the risk group performed less well than their normal age-mates in such tasks as search for a toy hidden under a cap; prediction of linear movement; or discrimination of size, form, or colour. The differences between the normal and risk groups remained when the groups were equated for developmental age. Thus even slight defects of basic visual functions in early infancy may correlate with the mental development of a child. Detailed analysis showed that reduced visual acuity (non-attention to small visual objects such as crumbs 0.5 – 1 mm in diameter in the acuity test) was especially prognostic.
Multiple Visual Latency
Authors: Allik J , Kreegipuu K
Published: December 2015

It has long been known that the time taken to detect a dim visual stimulus is longer than that to detect a bright one, with a relative delay of up to several tens of milliseconds. Systematic studies of various phenomena demonstrating this delay have revealed that the perceptual latency decreases monotonically as the stimulus intensity increases. Because latencies measured by psychological methods and cortical evoked responses are very similar to electroretinogram latencies, it has become a common belief that there is little in the intensity-dependent latency function that cannot be explained by retinal processes. We report evidence that there is not one absolute visual delay common to the whole visual system, but that the delay varies considerably in different perceptual subsystems. The relative visual latency was found to be considerably shorter in a movement-discrimination task than in other perceptual tasks which presume visual awareness of the onset of visual events, or of their temporal order.
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.
Multiphasic Spatial Response to Flickering Stimuli
Authors: Manahilov V
Published: December 2015

If it is assumed that the weighting function of early vision can be described by a spatiotemporal Gabor-like function (Manahilov, 1995 Vision Research35 227 – 237), the spatial impulse response to flickering stimuli would consist of more alternating phases than that to a brief stimulus. To test this prediction, the Westheimer paradigm and the brightness matching technique were used. The effect of a flickering inducing disk (temporal frequency 7.7 Hz, duration 195 ms, zero starting phase) of variable radius on the apparent brightness of an incremental test stimulus (1.2 min arc radius, duration 14.25 ms) was measured in foveal photopic vision. The test stimulus was superimposed on the centre of the inducing disk and presented 142 ms after the onset of the inducing stimulus. When the radius of the inducing stimulus was increased, the test brightness was enhanced, reaching a maximum at a radius of 3 min arc, then diminished below the control level at radii of 9 – 11 min arc and was enhanced again at radii of 14 – 17 min arc. This finding differed from the unimodal effect of a brief inducing disk on test brightness and suggested a multiphasic profile of the spatial impulse response to a flickering stimulus. This suggestion was supported by the dependence of the apparent brightness of a test line on the distance between the test and two flanking inducing lines. The temporal conditions were similar to those of the previous experiment. The brightness of the test line was increased above the control level at distances of 0 – 2 min arc, decreased at distances of 3 – 6 min arc and again increased to a smaller extent at distances of 10 – 13 min arc. Brief inducing lines evoked only the initial enhancement of the test-line brightness and its decrease at lateral positions. The data obtained are in line with the predictions of the model of the visual weighting function.
Afferent vs Efferent Motion Evoked Potentials: Relationship to Dynamic Visual Performance
Authors: Rutschmann R M , Wist E R
Published: December 2015

Visual evoked potentials (VEPs) were elicited by a computer-generated random-dot kinematogram in which a Landolt ring target moved from monitor centre to the right in front of a stationary background. Motion contrast was varied in terms of percentage of moving pixels within the ring (100%, 50%, 30%, 20%, 10%). Subjects indicated one of four gap locations (left, right, upper, lower) while fixating a small dot which was either screen centred (afferent task) or centred within the moving Landolt ring (efferent task). Correctly reported gap locations and reaction times were recorded as well as N2-amplitudes and N2-latencies. Decreasing contrast lead to decreased correct responses, decreased N2-amplitudes, and increased reaction times which were linearly correlated with increased N2-latencies. While these effects were obtained for both the afferent and efferent tasks, they were significantly stronger for the latter. At 10% motion contrast, efferent reaction times and peak N2-latencies were as much as 370 and 100 ms greater, respectively. To determine whether the stronger efferent effects were due to differences in retinal afference between the two conditions, a third stimulus was employed in which the retinal image motion of the efferent task was simulated in the absence of eye movements (stationary fixation point and Landolt ring on a leftward moving background). The effects on performance and N2-latencies and amplitudes obtained fell between those of the two initial conditions. Implications of these findings for the processing of afferent vs efferent dynamic visual stimuli and their relationship to VEPs are discussed.