bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
An Illuminated Surface May be Perceived as a Shining Surface
Authors: Menshikova G , Lunyakova E 
Published: December 2015

The relationship between the whiteness of a surface ( W) and its perceived illumination ( E) has been described by the equation: W + kE = Y, where Y is brightness and k is a constant. When brightness remains constant and perceived illumination decreases, whiteness increases from black to white. If, starting from a pair of values W = W0, E = E0 (where E0 is a low value of perceived illumination) at which the surface is seen as white (state A), E is further decreased while brightness remains constant, the surface may be perceived as shining (state B). We investigated the conditions under which the perceptual transition from state A to state B occurred. The subject looked at an illuminated white paper screen on which objects cast shadows. Two test patches were presented: one on a well-illuminated area, the other on a shaded area. The scene and the patches were illuminated by two separate light sources. The brightness of the patches was held constant. The subject was instructed to set the ‘scene’ illumination so that a test patch was perceived as shining, separately for each patch. The results showed that the ‘scene’ illumination where the transition occurred was different for the shaded and the well-illuminated patches. We conclude that the perception of a surface as shining depends on local illumination.
Genetic Studies of Macular Pigment
Authors: Alexander E C , Moreland J D 
Published: December 2015

One of the major functions suggested for macular pigment is to protect the retina. However, a tenfold variation in pigment level is observed in the general population, which cannot be explained by other factors, such as age, sex, race, eye or skin colour (Bone and Sparrock, 1971 Vision Research11 1057 – 1064). We aim to examine the role of genetic factors in this variation. In our first experiments (Alexander and Moreland, 1996 Perception25 Supplement, 105) we used colour matching to examine pigment levels in 23 local families. The highest correlation was seen for the father/child relationship where a linear regression accounted for 25% of the variance ( p<0.01); no significant relationship was observed for mother/child, grandparent/grandchild, or, as expected, for the control parent/parent plot. These families, and a few new ones, have been retested by a motion photometry paradigm, with a foveal 2 deg field and an extrafoveal annular field at 5 deg eccentricity. In the tests, a grating of alternating bars (460 nm and 580 nm) moves horizontally across the field at 14 Hz. The subject adjusts the luminance of the 580 nm bars for minimum perceived motion. The difference in setting between the two fields is used to measure the subject's pigment level. Analysis of preliminary data shows no significant correlation for any of the relationships but further analysis is in progress.
Visual Motion Perception and Field Dependence
Authors: Baumberger B , Martin R , Flückiger M 
Published: December 2015

The aim of this research was to throw light on the relationship between the visual field dependence, as measured by a rod-and-frame test (RFT), and the amount of recorded postural sway subsequent to a visual motion of the environment. Two groups of fifteen adult participants were split according to their results in an RFT test. They were asked to maintain an upright stance within a large-scale scenery animated by a texture flow generator. The flow consisted of either an approaching (AP) or a receding (RE) texture with respect to the observer. An ELITE system recorded antero - posterior body sway after onset and offset of stimulus motion. Both field-dependent (FD) and field-independent (FI) participants showed little reaction to AP whereas only FD participants presented a forward shift in the direction of RE at the onset. Postural responses opposite to AP and RE were marked for both groups at the offset. In conclusion we may assume an interaction between the direction specificity of the sways and a greater field dependence.
A Method for Measuring Apparent Illumination
Authors: Petrov A P , Maximov V V , Maximov P V , Orlov O Y , Kim C Y , Seo Y S 
Published: December 2015

Knowledge of perceived illumination is very important for almost all experimental investigations in colour science. We consider here a method for measuring apparent illumination based on the perceptual phenomenon of fluorescence. The underlying hypothesis is that the minimal illumination level at which a patch begins to look fluorescent exactly corresponds to the respective chromatic component of the apparent illumination in the scene. We report results of three experimental studies: (1) measurements of apparent illumination for a flat mondrian presented on a screen and mondrians made of paper presented in a specially designed box with controlled illumination observed monocularly; (2) measurements of apparent illumination in a ‘rich’ 3-D scene; (3) measurements to test the linearity of the subjective illumination space. The results confirm the basic hypothesis of the relation between fluorescence phenomena and perceived illumination and demonstrate that the proposed method gives reliable and accurate values for each of its chromatic components (errors were in the range 4% – 10%), eg for paper mondrians there was a strong correlation between the level and colour of illumination and the fluorescence. In the case of mondrians presented on a screen in darkness the measured apparent illumination was found unstable, however, as would be expected given that the context of such a scene is insufficient for a unique solution of the photometric problem. In the second experiment we found that the measurement results remain constant when the context of a ‘rich’ 3-D scene is changed and that they follow the changes in illumination conditions. In the third experiment we found that the linear relation f = f1+ f2 holds for the measured apparent illumination ( f) produced by combining of two other apparent illuminations ( f1, f2).
Accurate Recovery of Structure from Motion under Perspective Projection
Authors: Hogervorst M A , Eagle R A 
Published: December 2015

For small objects rotating over a small angle, the 3-D structure and motion are inseparable. Increasing the angle of rotation helps to define image accelerations while increasing the angular size of the object produces greater perspective effects. Both of these cues could be used by the visual system to disambiguate the structure and motion. In a 2 × 2 design we tested the influence of angular size (8 deg ‘S’ or 32 deg ‘L’) and projection type (perspective ‘P’ or orthographic ‘O’) on the perceived dihedral angle of vertically hinged planes (‘open books’). Stimuli depicted hinged planes with dihedral angles ranging from 35° to 169° rotating over angles ranging from 2° to 58°. The task of the subjects was to match the perceived dihedral angle to that of a probe defined by motion, texture, and binocular disparities. Spearman rank order correlations of subjects' settings with the simulated dihedral angles were high in condition LP ( r=0.93) and decreased in the order LP>=SP>=SO>=LO. In the same order, correlations with the total displacement of the projected points increased, up to r=−0.94 in condition LO, indicating that structure and motion become more and more confounded. While for small rotations and small dihedral angles, the settings are heavily influenced by the amount of rotation, for larger rotations and larger dihedral angles settings are more constant over rotation. These results show that both image acceleration and perspective effects play an important role in increasing the veridicality of perceived structure from motion.