bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal Integration of Alternately Exposed Monocular Images of a Random-Dot Stereogram
Authors: Pieper W
Published: December 2015

J R Ewald and O Gross (1906 Pflügers ArchivCXV 514 – 521) reported that monocular half-images presented alternately can be fused to a stereoscopic percept. The situation is like looking through a fence close to the eyes, with picket and gap widths being identical to the interpupillary distance. Though vision is monocular, an observer moving fast enough parallel to the fence will have stereoscopic vision of the scenery behind it. Little is known about the limits of this integrating mechanism.

In two experiments, LCD shutter glasses were used to control the viewing conditions of the anaglyphs of a random-dot stereogram. Binocular fusion was supported by a visible binocular fixation mark and a frame around the display. Subjects were eight male and three female students with normal stereoscopic acuity. They were instructed to press a key as long as they could perceive a global figure portrayed in the stereogram (25 min arc disparity). In experiment 1, monocular exposures to the right and the left eye followed each other without pauses. Psychophysical procedures were used to determine the frequency threshold for stereopsis. A breakdown frequency of 2.5 Hz was found, for descending as well as ascending series. Transferred to the concrete example of a fence, the result corresponds to a pace of 0.32 m s−1, with an interocular distance and a fence measure of 63 mm. In experiment 2, alternating monocular exposures of 100 ms duration were separated by variable pauses. Stereopsis disappeared with 8 ms pauses (ascending), and 17 ms pauses (descending). Results may be attributed to integrating mechanisms of binocular cortical cells, rather than to retinal processes (afterimages).
Interruption of Late Visual Processing Causes an Attentional Blink
Authors: Ehrenstein A , Breitmeyer B G , Pritchard K K , Hiscock M , Crisan J
Published: December 2015

When the task is to detect two letter targets in a stream of non-letter (digit) distractors in rapid serial visual presentation, an attentional blink (AB; ie a deficit in the detection of a second target when it follows the first by approximately 100 – 500 ms) is often found to occur. In a series of four experiments with different numbers of display positions, with or without masking, we show that: (1) the AB, which occurs when all items are presented at the same display location, is reduced when targets and distractors are presented randomly dispersed over 4 or 9 adjacent locations; (2) the AB is reduced with the spatially distributed presentation even when backward masks are used in all possible stimulus locations and when the location of the next item in the sequence is predictable; (3) the AB is not due to either a location-specific forward or backward masking effect occurring at early levels in visual processing.

We conclude that the AB is primarily a function of the interruption of late visual processing produced when the item following the first target occurs at the same location. It seems that, in order for the AB to occur, the item following the first target must be presented at the same location as that target so that it can serve both as a distractor and as a mask interrupting or interfering with late visual processing.
The Effects of Attentional Spread and Attentional Effort on Orientation Discrimination
Authors: Spitzer H , Sade A
Published: December 2015

We investigated the spatial properties of visual attention, and its relation to attentional effort. We show that stimulus detectability changes as a function of attentional beam width and of the degree of task difficulty. We used a matching-to-sample paradigm, presenting two Gabor patches simultaneously as sample stimuli and as test stimulus, the stimuli being at three different distances. Task difficulty was graded by changing the orientation difference of the two Gabor patches on nonmatching trials. ‘Difficult’ nonmatching probe trials were embedded within an easy block of trials (easy condition), and vice versa for ‘easy’ probe trials. Differences in the detectability, d', between probe trials in the two conditions were taken as a measure for the change in attention. Our results show that the detectability of a pair of stimuli decreases with an increase in the distance between stimuli. In addition, the results indicate an increase in attentional effort for different attentional beam widths, and also suggest a decrease in the SD of the internal stimulus representation during the task conditions that require more attention.
Perceptual Salience of Borders between Coloured Regions
Authors: Maloney L T , Yang J
Published: December 2015

Difference measurement is a little-used but potentially valuable method for studying suprathreshold vision. We used it to investigate the perceptual salience of borders between adjacent uniformly coloured regions. In these experiments, the observer viewed pairs of colours C1, C2 presented simultaneously in two rectangles, sharing a common border, centred on a neutral background. On each temporal 2AFC trial, the observer saw two colour pairs ( C1, C2) and ( C3, C4), and was asked to judge which of the two colour borders was more salient (stronger). In a single condition of the experiment, the colours C1, C2, C3, C4 were drawn from a set of ten colours constrained to lie along a fixed line segment in LMS space extending from the neutral background point (NBP) in a particular direction in LMS colour space.

Let D i denote the distance of C i from the NBP in LMS space. A difference measurement model accounts for such data if and only if there is an increasing ‘scale’ f( D) such that ( C1, C2) is judged more salient than ( C3, C4) precisely when f( D2) - f( D1) > f( D4) - f( D3). For each of three observers and eight directions, we found that estimated functions f( D) were concave, resembling power functions with exponents between 0.64 and 1.
Stages of Orientation Coding Assessed by the Tilt Aftereffect
Authors: Anderson R , Georgeson M A
Published: December 2015

We investigated orientation coding via the spatial-frequency tuning of the tilt aftereffect (TAE). In the single-adaptation condition, subjects adapted to single gratings of 1 or 8 cycles deg−1, 40% contrast, tilted 15° clockwise or anticlockwise from vertical; in two double-adaptation conditions the 1 and 8 cycles deg−1 gratings were superimposed at opposite orientations (‘plaid’ condition) or at the same orientation (‘parallel’ condition). Test gratings of 1, 2, 4, and 8 cycles deg−1, 20% contrast, were presented for 150 ms in an interleaved staircase procedure that measured the TAE by nulling it, hence making a tilted test grating appear vertical. Initial adaptation was for 3 min, topped up for 2 s between test presentations.

Results from the single-grating condition indicated broad spatial-frequency tuning of the TAE, since the effect was still strong when tested three octaves away from the adapter. In the parallel condition, the TAEs were around the average of those reported in the single condition. Negligible TAEs were found in the 1+8 cycles deg−1 plaid condition, indicating that opposing adaptations had effectively cancelled each other out. These findings strengthen the suggestion of Olzak and Thomas (1992 Vision Research32 1885 – 1898) that orientation is encoded via an integrative mechanism which pools or sums the outputs of different spatial-frequency channels, and further imply that much of the adaptation responsible for the TAE occurs at this later broad-band stage.
Relative Size Perception at a Distance is Best at Eye Level
Authors: Bertamini M , Yang T L , Proffitt D R
Published: December 2015

We studied the role of the horizon line as a source of information about the relative size of objects at a distance. Relative-size judgements (2AFC) were collected for two objects at 30.5 m and 23.8 m away from the observer to assess how performance depends on the relationship between the size of the objects and the eye level of the observer. In three experiments in an indoor hallway and in one experiment outdoors, accuracy was higher for objects in the neighbourhood of eye level. We consider these results in the light of two hypotheses: one which proposes that observers localise the horizon as a reference for judging relative size, ie on the basis of the horizon ratio, and another which proposes that observers perceive the general neighbourhood of the horizon and then employ a height-in-visual-field heuristic. The finding that relative-size judgements are best around the horizon implies the use of information independent of distance perception in perceiving size.
A Method of Identification of Analyser Characteristics That is Free of Probability Summation Effect
Authors: Logvinenko A D
Published: December 2015

A detection model (originally proposed by Quick) comprising, in a sequence of linear analysers, varphi1, …, varphi n, nonlinear transducer functions, and the Minkowski decision rule, is widely used, especially when it is necessary to take into account the effect of probability summation. However, there is a general belief that the analyser characteristics cannot be determined in detection experiments since there is a trade-off between these characteristics and the decision rule. Here we show how to overcome this problem, ie how to identify the analysers varphi1, …, varphi n despite the probability summation between them.

The observer's performance is assumed to be quantitatively defined in terms of an equidetection surface (EDS). Each analyser varphi i is expressed as a weighted sum of linear (coordinate) analysers {phi j}: varphi i=sum j=1 n a ijphi j, so that an identification of the analysers {phi i} is then reduced to evaluating the weight matrix A={ a ij}. It has been proven that A can be uniquely recovered from an ellipsoidal approximation of EDS in the neighbourhood of at least two points. More specifically, the following equation holds true: A−1 DA= H1−1 H2, where D is a diagonal matrix, H1 and H2 are the matrices of the quadratic forms determining the n-dimensional ellipsoids approximating EDS. Thus, the matrix H1−1 H2 known from experiment is a similarity transform of the diagonal matrix, the columns of A being the eigenvectors of H1−1 H2. Hence, any eigensystem routine can be used to derive A from H1−1 H2.
Perceived Velocity in Dynamic Random-Dot Patterns is Influenced by Noise Type
Authors: Owen K A , Raymond J E , Thompson P
Published: December 2015

Local motion signals can be pooled to detect the direction of coherent motion in random-dot kinematograms (RDKs) having a high proportion of random noise. Noise type does not appear to affect direction discrimination in such displays (Scase et al, 1996 Vision Research36 2579 – 2586). We have observed that RDKs with low coherence yet an obvious global direction appear to move slower than similar RDKs with high coherence. Using judgements of relative speed between RDKs containing different proportions of noise in a 2AFC paradigm we have quantified this effect and sought to determine if the type of noise influences perceived velocity.

Levels of coherence in all dot patterns were well above the thresholds for directional judgements. Dots were assigned as ‘Noise vs Signal’ randomly on each frame of the RDK. Noise dots were either of type ‘random position’ or of type ‘random walk’. Position noise dots were randomly repositioned within the area of the display on each frame and had an isotropic distribution of directions and variable speeds. Random-walk dots moved at the same speed on successive frames (their displacement matched to that of the signal dots) but in a randomly chosen direction.

The two noise types yielded statistically different results. In RDKs containing random-walk noise, decreasing the coherence of the display (30% signal, 70% noise) reduced perceived velocity (on average to 0.75 of the actual velocity), while increasing the coherence of the display increased perceived velocity until at high coherence levels (80% signal, 20% noise) the perceived velocity approximated the veridical velocity (on average 0.96). The proportion of position noise in a display had no effect on perceived velocity. These basic results are discussed in relation to current models of motion detectors and velocity perception.
Categorical Perception of Illusory Contour Defined Shapes
Authors: Kovács G , Köteles K , Hosseinalikhani M , Lõrincz A
Published: December 2015

Categorical perception (CP) is the phenomenon when people are better able to distinguish between stimuli of different categories than between stimuli of the same category and it appears for innate and learned stimuli of various sensory modalities. We tested if CP occurs also for illusory contour stimuli.

First, in an ABX paradigm the shape discrimination capacity of subjects was tested for convex (‘fat’) or concave (‘thin’) Kanizsa-square-like shapes (cf Rubin, 1996 Perception25 Supplement, 3; pre-category-learning test). The proportion of correct responses and response latency were measured. Second, subjects were instructed that every stimulus belongs to either the ‘fat’ or the ‘thin’ category, and they were trained to categorise the individual stimuli using a 2AFC paradigm with corrective feedback until 90% of correct responses. Third, we measured the shape discrimination capacity of subjects, by repeating the first ABX paradigm (post-category-learning test). Comparison of the ratio of correct responses in the post/pre discrimination tests showed that discrimination of illusory shapes of different categories is enhanced but discrimination of members of the same category is made more difficult by category training. In a second experiment, by increasing the physical differences between the extreme ‘fat’ and extreme ‘thin’ stimuli (increased range of the opening-angle of the Kanizsa-square inducer pacmen), we made the categorisation task easier for the subjects and tested if discrimination capacity is altered by the modified difficulty of the categorisation task. We discuss the effect of difficulty on CP and the relation of illusory CP to that of real luminance contour stimuli.
A Dynamic Type of Vernier Acuity in the Visual Prediction of Motion Trajectory
Authors: Yamazaki R , Asano E
Published: December 2015

The purpose of the experiment was to analyse a dynamic type of Vernier acuity in the visual prediction of the trajectory of linear apparent motion. The subjects were shown a single moving dot, which moved from the left end to the right end of a CRT. The change in dot position between two successive frames was 0.15 deg. Midway through the trajectory the dot moved behind an amodal occluding square, thus being invisible in this area. The vertical position where the dot re-emerged from behind the occluding square was varied, with 14 conditions for deviations both above and below the ‘correct’ locus of straight movement. A unit step of the deviation was 0.029 deg. There were three SOA conditions (13 ms, 21 ms, and 26 ms). In a 2AFC paradigm, the subjects had to report on which of two presentations the dot reappeared in the ‘correct’ position.

We applied Probit analysis to fit a cumulative normal distribution to the result of each SOA condition and each deviation direction. We defined a value giving 75% correct response as a threshold value. Within each SOA condition, there was no difference between the threshold for deviations above or below the correct position, nor did threshold values between three SOA conditions show significant differences (ANOVA). We compare and discuss Vernier-acuity thresholds with and without amodal occlusion of the locus.
Adaptation to Contingencies in Macaque Primary Visual Cortex
Authors: Carandini M , Barlow H B , Poirson A B , O'Keefe L P , Movshon J A
Published: December 2015

We tested the hypothesis that neurons in the primary visual cortex adapt selectively to contingencies in the attributes of visual stimuli. We recorded from single neurons in macaque V1 and measured the effects of adaptation either to the sum of two gratings (compound stimulus) or to the individual gratings. According to our hypothesis, there would be a component of adaptation that is specific to the compound stimulus.

We performed two sets of experiments. In the first set one grating had optimal orientation and the other was orthogonal to it. In the second set the gratings were parallel, differed in spatial frequency, and were both effective in driving the cell. The first set of experiments, but not the second, provided evidence in favour of our hypothesis. In most cells tested with orthogonal gratings, adaptation to the compound stimulus reduced the responses to the compound stimulus more than the responses to the preferred grating. In addition, in most of these experiments the responses to the compound stimulus were reduced more by adaptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation in the experiments with orthogonal gratings was specific to (and caused by) the contingent presence of the two gratings in the compound stimulus.
Oppel-Kundt Illusion and Visual Field Anisotropy
Authors: Bulatov A , Bertulis A , Kocaniene J
Published: December 2015

Psychophysiological experiments are reported in which a combined influence of visual field anisotropy and the Oppel - Kundt illusion on length judgement was tested. The subjects adjusted the test interval of a stimulus to be equal with the reference interval in length. The stimuli—three dots or the Oppel - Kundt figure with ten dots within the filled half—were generated on the monitor. In the Oppel - Kundt figure, the filled half was considered as the reference interval, and the empty half as the test one. In sessions of the experiments, values of errors as functions of the size and orientation of the stimulus were measured. The reference interval varied within 14 – 150 min arc range, and the orientation was fixed in the 0°, 90°, 180°, or 270° position. The orientation of the test interval varied from 0° to 360°, in 7° steps. The experiments with the three-dot stimuli yielded pure characteristics of visual field anisotropy, and the experiments with the Oppel - Kundt figure showed combined appearance of both the anisotropy and the illusion. The data demonstrate an algebraic summation of the two factors in a simultaneous manifestation. It is assumed that estimation of symmetry of the stimulus, in accordance to the bisector of its internal angle, provides discrimination of the length. Calculations have shown a satisfying confirmation of this assumption.
Visual Illusions in Frogs and Toads
Authors: Bastakov V A
Published: December 2015

There are situations where frogs and toads radically misjudge the size of a moving object, taking an enemy for prey or vice versa. In the present work, the conditions where this occurs were investigated. Frogs ( Rana temporaria) were shown black balls of diameters 0.25 – 20 cm moving at different distances and velocities, either in the presence or absence of a structured background. When the targets moved at 10 – 15 cm s−1 (at a distance where this corresponded to ∼10 deg s−1) in the presence of the background, frogs turned, approached and tried to catch those with small diameters (0.25 – 2 cm) only. Larger targets mainly evoked escape reactions. Without the background, balls of any real size could be perceived as prey: all targets of angular size about 5 deg or less triggered a ‘food’ turning reaction, implying that the critical distance for this reaction depends linearly on object size. ‘Food’ turning towards big targets (10 or 20 cm) indicates incorrect distance estimation. Moreover, if a big target was moved at high speed (100 deg s−1), the frog not only turned but also flicked its tongue at it without approaching it, even when the distance was up to 1 m. Observations on the toad Bufo bufo were qualitatively similar. Thus it is possible to create an illusion of closeness in frogs and toads by increasing the speed of the moving object. Conversely, it is possible to create an illusion of distance by moving a small object at slow speed close to the animal. The 0.25 cm target moving at a 12 cm distance with a velocity of 0.15 cm s−1 (0.7 deg s−1) in the absence of the structured background evoked the ‘food’ reaction on only 4% of the trials and escape reactions on 80% of the trials. When the background was present, the same stimulus evoked ‘food’ turning only. The escape reaction to a small object can be explained by a drastic overestimation of its distance in the absence of other cues.
Adjustment of Collinearity of Laterally Moving, Vertically Separated Lines Reveals Compression of Subjective Distance as a Function of Aperture Size and Speed of Motion
Authors: Bachmann T , Kalev K
Published: December 2015

We have investigated the effects of the size of the aperture and the speed of motion of a pair of laterally moving vertical lines on the precision with which subjects were able to adjust the spatial position of these moving lines so as to achieve subjective collinearity. The reference line moved laterally across the whole computer display (14.4 deg) while the upper line (that was vertically separated from the reference one by 0.64 – 2.56 deg) appeared in a central aperture of varying horizontal width (0.62 – 1.9 deg). In each trial subjects shifted the aperture line leftwards and/or rightwards until it seemed collinear with the ‘permanently’ moving line. In order to achieve subjective collinearity the aperture line had to be shifted towards the direction of motion from the position that would have satisfied physical collinearity. The size of these shifts (up to 0.124 deg) was a monotonically increasing function of the speed of motion and a monotonically decreasing function of the diameter of the aperture. The results point to the compression of subjective space-time as a monotonically decreasing function of the spatiotemporal availability of the aperture stimulus. The longer the exposure of the aperture stimulus, the more its perception ‘caught up’ the initial delay compared with the perception of the moving reference stimulus. We may postulate a relative acceleration of establishing subjective conscious representation with increasing temporal availability of the stimulus. Similarities with the Fröhlich effect and tandem effect are discussed.
Stimulus Location is Processed Faster than Stimulus Colour
Authors: Rossetti Y , Pisella L , Arzi M
Published: December 2015

There is a convergence of anatomical, electrophysiological, neuropsychological, and psychophysical data to support the dissociation of visual pathways into two main streams projecting from occipital to frontal cortex via the posterior parietal lobe (dorsal route) and via the inferotemporal lobe (ventral route). It is usually assumed that the dorsal route provides information that is useful for driving an action toward the stimulus (ie metric properties, such as localisation), whereas the ventral route extracts information useful for identifying it (ie intrinsic properties, such as colour). It is known that pointing movements can be reoriented to a novel target location within a short delay (about 110 ms), even when the target jump cannot be detected because of saccadic suppression. Electrophysiological studies have suggested that inputs to the dorsal pathway have a latency shorter than inputs to the ventral pathway.

We compared latencies of visuomotor processing for colour and location during a pointing task. Target location and/or colour were altered upon movement onset. Instructions were to correct movement direction or to interrupt the movement according to the target change. We found that in both cases colour processing was slower (by about 100 ms) than location processing of the same target. Performance observed for identical movement speed was always higher for location responses whereas movement duration spontaneously chosen by subjects was longer when they had to process colour. Strikingly, corrections were also observed with the interruption instruction. We conclude that (1) colour is processed more slowly than location, and (2) automatic corrections can be observed prior to response inhibition for fast movements.
Further Evidence of the Effect of Gradient on Lightness
Authors: Agostini T , Galmonte A
Published: December 2015

Recently, Agostini and Galmonte (submitted for publication) reported a new effect of gradient on lightness. When two identical mid-gray squares are placed at the centre (white and black, respectively) of two crosses, the first cross having arms filled by a constant achromatic gradient from black (outer part) to white (inner part), and the second cross being the negative of the first one, the gray target surrounded by white appears much darker than that surrounded by black. In a simultaneous comparison, this phenomenon is much stronger than the classical lightness contrast effect. Further observations showed that the effect is quite robust also when the amount of black area is reduced and the gradient is discontinuous. When the gray targets are enlarged to fill the centres of the crosses, the effect is still stronger than that observed in the classical simultaneous lightness contrast display. Furthermore, the effect is independent of the shape of the configuration. The phenomenon can be explained by assuming that the gradient is perceived as a change of the level of illumination rather than as a change of the reflectance of the surfaces.
Implicit Learning of Temporal Discriminations in Perception
Authors: Virsu V , Aura M
Published: December 2015

We measured the temporal accuracy of signal transfer in the brain by means of periodic pulse stimuli in various sensory modalities using an adaptive threshold algorithm. Trains of supra-threshold signal pairs in 0° or 180° phase shifts appeared, and the subject indicated whether the signals of each pair in a train were simultaneous or not at various nominal frequencies of the pairs. The signals were spatially separate flashes of light, clicks, tactile pulses, or combinations thereof in intermodal comparisons. Temporal discrimination thresholds involving one signal in central photopic vision and the other in audition or tactile presentation to the finger tips did not exceed frequencies from 3 to 8 Hz, and in vision alone the average synchronism thresholds were about 10 Hz (SOA 0.05 s with 0.008 s pulses). The practice derived from 9 experimental sessions during 6 weeks improved temporal accuracy by factors ranging from 1.2 to 2.0 on the average in a sample of 33 naive subjects (university students), although no explicit feedback was given. The practice effect was lasting, for the average performance decrement was only 9% in 7 months. Thus, a considerable temporal modifiability must exist in the brain because a large learning effect was found in the simple temporal synchronism discrimination tasks.
Performance of Eye-Tracking Movements in Otoneurological Patients
Authors: Savov A , Damianova V , Najdenova V
Published: December 2015

Eye movements were recorded in patients with vertigo as they were tracking a horizontally moving object. Effects of the colour of the object (white, yellow, green, blue, violet), the direction of motion (left - right or right - left), and of the caloric test on the left and on the right side (water temperature 30 °C) were investigated. We present a computerised method for objective, quantitative, and precise assessment of the data. The main indices recorded were: duration and relation between the phases, character of the peaks, disorganisation of the movements (if observed), and movement amplitude and area.

The results show that the experimental variables do affect the measured parameters. For example, durations were longer in yellow light (left - right direction) and for red colour (inversion movement), compared with movement in either direction for white, green, and blue. The caloric test shortened time periods and increased amplitudes in most of the conditions. A model of the process based on Fourier analysis is being developed. The aim is to use the proposed method for assessing disease-related changes and the effectiveness of therapy.
Dynamic Spatiotemporal Restructuring of Visual Receptive Fields through Selective Attention: A Model
Authors: Suder K , Funke K , Woergoetter F
Published: December 2015

Cells in the lateral geniculate nucleus (LGN) strongly change their behaviour covarying with different EEG states. During sleep and drowsiness (synchronised alpha, delta-wave EEG) short transient responses prevail whereas during a desynchronised ‘alert’ EEG (beta-waves) long-lasting tonic responses are observed. We propose that this is part of a mechanism used to restructure the spatial and temporal characteristics of the receptive fields in LGN and cortex reflecting changing states of selective attention. To this end we present a model of the primary visual pathway using integrate-and-fire neurons to simulate the afferent signal flow (retina, LGN, V1). The model also implements excitatory topographically arranged lateral intracortical and corticofugal connections which act as a positive feedback and trigger spatial winner-takes-all (WTA) mechanisms enhanced by lateral inhibition at both levels. Furthermore, the LGN membrane characteristic can switch from phasic (hyperpolarised) low-threshold Ca2+ bursting mode to tonic (depolarised) signal-transmission mode. Switching is triggered by feedback and amplified by intracellular intrinsic positive-feedback mechanisms in the model LGN. All positive-feedback mechanisms are subject to damping such that they remain ineffective below a certain threshold. Salient stimuli which ‘attract attention’ will push the system above threshold and a self-amplifying process is started which sharpens the cortical receptive fields spatially (by spatial WTA) and drives the winners in the LGN into signal transmission mode (by intrinsic intracellular mechanisms). These results predicted by the model are in accordance with LGN cell behaviour. In addition, the model predicts that cortical receptive fields should be wider during synchronised EEG than during desynchronised EEG.
Developmental Demands for Successful Measurement of Visual Acuity in Pre-School Children
Authors: Kulikova S V
Published: December 2015

Adequate application of the Lea symbol and BUST visual acuity tests (Hyvarinen et al, 1980 Acta Ophthalmologica58 507; Lindstedt, 1986 British Journal of Visual Impairment4 49), designed for children over 18 months of developmental age, in young and/or handicapped pre-school children require preliminary assessment of their level of development. To assess the developmental demands more precisely, 162 children aged from 15 to 35 months and 54 older pre-schoolers, most with normal vision, were examined. Nearly half of the children showed some developmental delays in physical and mental capabilities as assessed on the CDI scale (Ireton, 1992, Child Developmental Inventory, Behavior Science System Inc). Nevertheless, in 77% far and/or near visual acuity was successfully measured by combinations of Lea symbol and/or BUST tests. The youngest successful children, 18 and 20 months of age, passed BUST-N and Lea-Domino. For children aged 18 – 24, 24 – 29, 30 – 35 months, and 36 months and above the success rates were, respectively, 39%, 75%, 89%, and 96%. The minimal values of the CDI scale indexes among the successful children may be regarded, in addition to chronological age, as minimal developmental demands, ie conditions necessary, although not always sufficient, for the child to pass visual acuity measurements. These values in months were 16 (‘social’), 18 (‘selfserving’), 14 (‘gross motor’), 16 (‘fine motor’), 16 (‘speech development’) and 19 (‘language comprehension’). The value of the last index was the most critical. Since the developmental demands are not very high, there are good prospects of using Lea symbol and BUST tests in young and/or handicapped children.
Changes in the Functional Visual Field Due to Aging and Field Defects
Authors: Cornelissen F W , Kooijman A C , Ditvoorst H I A , Eppink E
Published: December 2015

We examined search performance throughout the functional visual field. This has been shown to be an important determinant for performance in daily life tasks. We were interested to see how aging affects performance and whether we could find evidence for compensatory strategies in subjects with visual field defects. The task was to localise a target (C) among 24 distractors (O) and identify the direction of its gap. Subjects were allowed to make eye movements. Using a staircase procedure, performed separately at each of the 25 possible target positions, we determined the stimulus presentation time necessary to reach criterion performance. This method has the advantage over more common reaction time experiments that it is not affected by speed - accuracy trade-offs. Seven young (age 22 – 28 years) and seven old (age 58 – 78 years) subjects with normal vision participated. In addition, we tested older subjects with visual field defects (central defects and hemianopia).

Our results show significant ( p<0.0001) age-related differences in the presentation time required for criterion performance. In addition, we found a significant ( p<0.0001) interaction between age and target eccentricity, with the largest age-related decline in performance occurring for targets on or near the initial fixation point, and smaller changes occurring for targets further away from this point. Age and target eccentricity turned out to be the main predictors for search performance. We conclude that age significantly affects search performance, but the extent depends on the distance from the initial fixation point. Our results therefore suggest that aging does not equally affect all stages in visual processing. Not surprisingly, field defects influence search performance, but we also found evidence for compensatory strategies.
Detection Time for Changes in Direction of Visual Motion
Authors: Mateeff S , Hohnsbein J
Published: December 2015

Subjects observed a random-dot pattern that moved within an invisible aperture. In experiment 1 the pattern moved horizontally for 0.9 s, then changed its direction of motion by an angle between 12° and 180° for a time t and returned to horizontal motion. The threshold duration t for detection of the direction change was measured for speeds of motion of 2, 4, 8, and 16 deg s−1. The thresholds decreased with increasing angle of change, reaching an asymptotic level of 10 – 15 ms at about 60° for speeds between 4 and 16 deg s−1. It is suggested that the asymptotic course of this relationship reflects the bandwidth of the directional tuning of the motion-detection system. In experiment 2 we found that the temporal thresholds for detection of a velocity reversal (180° change in direction) are equal to those for detection of an increase in speed by a factor of three, and that the time to detect an abrupt cessation of motion is nearly equal to the time for detection of a change in speed by a factor of two. Measures such as ‘delta’ contrast and Michelson contrast are shown to be inappropriate for describing the detection of these changes in velocity. We suggest that the absolute value of the vector difference V2- V1 between the velocities before and after the change may be a meaningful measure for the description of the detection performance.
Tools for Investigating the Perception of Natural Scenes
Authors: Pronin S V , Makulov V B , Harauzov A K , Chihman A V , Chihman V N , Shelepin Y E
Published: December 2015

Research on the perception of complex half-tone images and images of natural scenes requires accurate quantitative control of the characteristics of the stimuli. The tools consist of the hardware and the software for stimulation and processing. Our hardware for stimulation includes a CCD, an IBM PC with implementing Frame Grabber, the display, and a device for photometric control. We present programs for image processing allowing control of the brightness scale, reformation, changing the number of discretisation levels, addition and subtraction, programs for convolution operations including frequency filtration approximations, the means of different methods, programs for generation of test images and for generation of noise added to these, and programs for measuring statistical and geometrical characteristics of images. We also present software for use in electrophysiological experiments.
Visually Evoked Magnetic Field Induced by Ring Motion Aftereffect
Authors: Osaka N , Osaka M , Koyama S , Kakigi R
Published: December 2015

Motion aftereffect (MAE) is a negative aftereffect caused by prolonged viewing of visual motion: after gazing at a moving grating for a while, a stationary image will appear to move in the opposite direction (Ashida and Osaka, 1995 Vision Research35 1825). Evoked magnetic field (magnetoencephalogram: MEG) was measured when a human subject observing ring MAE in which concentric circles appear to contract continuously after viewing continuously expanding rings. The diameter of the stimulus was 20 deg with fixation point in the centre. The magnetic evoked field (80 averagings at a latency of 190 ms) was measured from 37 points over the occipital and parietal areas (Magnes SQUID biomagnetometer, BTi) while the subject was observing stationary rings after an adaptation period of 2 s at low spatial frequency (4 cycles deg−1, 4 Hz). The luminance profile was sinusoidally changed across rings. MRI image fitting (sagittal, coronal, and axial view) for each of four subjects, and dipole estimates obtained for equal magnetic field contours (with value of goodness of fit greater than 0.98) from the right brain hemisphere suggest that the main loci subserving MAE lie in the surrounding region over the lateral occipitotemporal areas in the human brain, close to area MT. This is in good agreement with another study with fMRI-based MAE measures [Tootell et al, 1995 Nature (London)375 139] in which a clear increase in activity in these areas was observed when subjects viewed MAE.
Symbolic Meanings of Computer-Generated Abstract Forms
Authors: Oyama T , Yamada H , Iwasawa H
Published: December 2015

In experiment 1, symbolic meanings of 32 computer-generated abstract figures were rated by 27 subjects (undergraduates) on eleven semantic differential scales. The stimuli were basically generated by sine waves on a circular line. Random fluctuation was added to half of the stimuli. The stimuli varied in five physical parameters: sine-wave frequency, amplitude, linearity, regularity, and the height/width ratio of the whole figure. A factor analysis on the results of ratings on the semantic differential scales revealed four factors: evaluation, activity, lightness, and sharpness, which correlated with the physical parameters of the stimulus forms as follows: evaluation with regularity ( r = 0.830), activity with frequency ( r = 0.806), lightness with regularity ( r = 0.631), and sharpness with linearity ( r = 0.782). In experiment 2, another group (54 subjects) had to match ten abstract words: happiness, anger, surprise, fear, anxiety, creativeness, destruction, time, eternity, and loneliness, with sixteen abstract forms [half of the stimuli from experiment 1, with constant height/width ratio (1.00)]. These abstract words were also rated by a third group of 26 subjects on the semantic differential scales. The results indicated that forms and words that were matched with each other were rated similarly on the semantic differential scales, and indicated the validity of the symbolic meanings of the forms measured in experiment 1.
Neuroimaging Analysis of Visual Motion
Authors: Osaka M , Osaka N , Koyama S , Kakigi R
Published: December 2015

The evoked magnetic field (magnetoencephalogram: MEG) was measured in human subjects observing random-dot motion. 600 random dots generated with VSG2/3 (Cambridge Research Systems) moved at about 10 deg s−1 (either in the 45° or the 135° direction). The motion frame (5 s) was followed by a stationary frame on a screen (projected from Barcodata 3100 projection system) subtending a visual angle of about 20 deg × 20 deg. Six subjects observed the motion frame presented in the left visual field. The magnetic evoked field (80 averagings) was measured from 37 points over occipital, temporal, and parietal areas (Magnes SQUID biomagnetometer, BTi) of the right brain hemisphere. Dipole estimates based on equal magnetic field contours (190 ms after motion frame onset with value of goodness of fit greater than 0.95) and MRI image fitting (sagittal, coronal, and axial view) for each subject suggest that the main loci subserving motion perception lie in the surrounding region over occipital, temporal, and parietal junction areas in the human brain close to area MT.
Spatial Integration of Objectively Equiluminous Chromatic Gratings
Authors: Kankaanpää M I , Rovamo J , Kukkonen H T , Hallikainen J
Published: December 2015

Contrast sensitivity functions for achromatic and chromatic gratings tend to be band-pass and low-pass in shape, respectively. Our aim was to test whether spatial integration contributes to the shape difference found at low spatial frequencies. We measured binocular chromatic contrast sensitivity as a function of grating area for objectively equiluminous red - green and blue - yellow chromatic gratings. Chromatic contrast refers to the Michelson contrast of either of the two chromatic component gratings presented in counterphase against the combined background. Grating area ( A) varied from 1 to 256 square cycles ( Af2) at spatial frequencies ( f) of 0.125 – 4.0 cycles deg−1. We used only horizontal gratings at low and medium spatial frequencies to minimise the transverse and longitudinal chromatic aberrations due to ocular optics. At all spatial frequencies studied, chromatic contrast sensitivity increased with grating area. Ac was found to be constant at low spatial frequencies (0.125 – 0.5 cycles deg−1) but decreased in inverse proportion to increasing spatial frequency at 1 – 4 cycles deg−1. Thus, spatial integration depends similarly on spatial frequency for achromatic (Luntinen et al, 1995 Vision Research35 2339 – 2346) and chromatic gratings, and differences in spatial integration do not contribute to the shape difference of the respective contrast sensitivity functions.
Rhodopsins with Similar Absorbance Characteristics but Different Rates of Thermal Activation: Amino Acid Sequences
Authors: Fyhrquist N , Donner K , Hargrave P A , McDowell J H , Popp M P , Smith W C
Published: December 2015

Thermal activation of the visual pigment is thought to be an important factor that in many cases limits the absolute sensitivity of vision in darkness. It has been suggested that pigments with high \lambdamax (ie with good absorbance at long wavelengths, allowing ‘red-sensitive’ vision) are associated with a cost in terms of high thermal activation rates, degrading signal/noise and hence visual sensitivity [Barlow, 1957 Nature (London)179 255 – 256]. While rhodopsins in different species do show a general correlation between red-sensitivity and high thermal activation rates as measured electrophysiologically in whole rods (Firsov and Govardovskii, 1990 Sensornye Sistemy4 25 – 34), a comparison of the toads Bufo marinus and B. bufo with the bull-frog Rana catesbeiana has suggested that the two properties are not tightly coupled. Toad and bull-frog rhodopsins have almost the same \lambdamax, yet the thermal activation rate in bull-frog rods is lower by almost one order of magnitude [Donner et al, 1990 Journal of Physiology (London)428 673 – 692]. We have sequenced the cDNA coding for the rhodopsins of the two toad species and that of the common frog R. temporaria and aligned them to previously sequenced rhodopsins of R. catesbeiana, R. pipiens and Xenopus laevis in an attempt to identify substitutions that could underlie the greater thermal stability of bull-frog rhodopsin compared with toad rhodopsins.

The open reading frame predicted proteins of 354 amino acids. There was 96% identity between species of the same genus and 90% identity between genera. Across the six species studied, there is a total of 22 non-conserved substitutions and changes that include gain or loss of hydroxyl groups. Our study produced a list of substitutions that apparently do not significantly affect absorbance characteristics. We could not, however, unequivocally identify substitutions important for thermal stability.
A Comparative Study of the Spatial-Frequency Spectrum of Different Letter Optotypes and its Role in Target Recognition
Authors: Koskin S A , Danilichev V F , Shelepin Y E
Published: December 2015

We studied the contrast sensitivity functions (CSFs) in patients with different eye and brain diseases using a computerised sinusoidal grating test with a wide range of frequencies (0.4 – 19.0 cycles deg−1), the Pelli - Robson chart and a new chart with frequency-filtered Snellen optotypes. The patients had different CSF curves with a decrease of contrast sensitivity in the low, middle, or high frequencies depending on their main disease (refraction anomalies, cataract, glaucoma, neuritis of optic nerve, brain tumours, etc).

Analysis showed that optotypes in the Pelli - Robson chart have a wide-range spatial-frequency spectrum, and optotype recognition is determined not only by low spatial frequencies. We find that the recognition of standard Sloan's optotypes is determined mostly by sensitivity in the range of 9.4 – 14.0 cycles deg−1. At the same time we measured contrast sensitivity using the new filtered Snellen optotypes. Our calculations support our earlier suggestions that the new filtered optotypes have a narrow-band spatial-frequency spectrum, thus enabling selective measurement of contrast sensitivity in each narrow frequency band.
Differential Effect of Object Complexity on 2-D and 3-D Matching Processes
Authors: Nishina S , Inui T
Published: December 2015

Previously, we found that two matching processes work in parallel when an object is recognised from unknown viewpoints: the 2-dimensional (2-D) and the 3-dimensional (3-D) matching process. These processes were shown to differ in several respects, including recognition speed, generalisation range, and learning ability. We have now examined the effect of the complexity of an object on these two matching processes. We performed a recognition experiment where the subjects had to compare two sequentially presented images. The stimuli were objects that had different numbers of segments, presented for either 1.5 s (short condition) or 3.0 s (long condition). The different presentation times enabled us to separate the two processes, as 3-D matching requires a longer processing time.

We adopted the ability to generalise from a known view as a measure of the performance of each process. Under the ‘short’ condition, the generalisation range for objects of high complexity was almost the same as that for objects of low complexity. Under the ‘long’ condition, however, the ranges for objects differing in complexity were significantly different. Our interpretation is that the effect of complexity was mainly associated with the 3-D matching process. The matching performed by the 2-D process under a shorter duration may be a simple image-to-image matching without recourse to the 3-D structure of the object.
A Study of the Abney Effect in Some Colour Atlases: Designing Opponent Variables and Hue Functions
Authors: Martínez-Verdú F , Pujol J , Artigas J M
Published: December 2015

The Abney effect in colour-appearance systems (Munsell, NCS) means that the lines for identical apparent hue (at constant lightness) do not coincide with the straight lines for constant dominant wavelength. The curvature of constant-hue lines in chromaticity diagrams reflects the fact that cone signals are nonlinear functions of the rate of photon absorption. The most widely used nonlinear intensity-response function in vision is the Naka - Rushton function, which in an intermediate range can be approximated by a square-root function. Our purpose has been to study the Abney effect in the Munsell and NCS colour atlases in order to develop a mathematical-physiological description on this basis, designing the redness - greenness and yellowness - blueness perceptual variables and the perceptual hue function in each colour system. The description is applicable to both biological and machine-vision systems.