bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preferred Hemifields Learn Less
Authors: Pavlovskaya M , Ring H , Groswasser Z , Hochstein S 
Published: December 2015

Subjects were tested on orientation and colour pop-out tasks. Orientation pop-out stimuli were 3 × 3, 5 × 5, or 7 × 7 arrays of vertical light (white) bars (on a black background) with a target element of diagonal (45°) orientation (present on half of the trials). Colour pop-out stimuli consisted of 60° oriented bars with blue distractor and yellow target elements (on a gray background). Inter-element distance was 40 min arc. The arrays were presented eccentrically, in the right or left hemifield, so that the distance of their centres from the fixation cross was 2.5 – 6.5 deg. First we tested performance in the right and left hemifields, with interleaved trials. Most subjects (7/9) had a right-hemifield preference for the orientation and/or colour task. The remaining 2 had a left-hemifield preference. For the six subjects tested on both tasks, all but one had more laterality for colour than for orientation. Thus, for the 15 conditions tested (9 orientation + 6 colour), most (8/15) showed better performance in the right hemifield; the minority (2/15) were better on the left; and a third were about equal in both hemifields. Subjects were recalled for a second session with the same tasks, to test improvement due to first session training. Almost all showed significantly greater improvement for the non-preferred hemifield. This effect was so strong that often preference was switched. Surprisingly, preferred-hemifield performance actually declined for many subjects. Thus, the effect seems related to competition, and perhaps an automatic attention-directing mechanism.
Measurement of the Shortening Effect on the Perceived Path of Stroboscopic Movement
Authors: Nozawa S 
Published: December 2015

When two vertical short lines are alternately flashed at certain SOAs, a shortening of the apparent path of the stroboscopic movement is perceived. In the experiments reported here, factors influencing the shortening effect were studied with lines created on a CRT display. Experiment 1 was designed to study the effect of SOA. Each stimulus line was always presented for 100 ms, but intervals were varied in the range from 25 to 800 ms. With short and long SOAs almost no shortening illusion was observed, whereas the SOA for optimal stroboscopic motion (200 ms) also produced the largest illusion (ca 16%). This agrees with the classic study by Scholz (1924 Psychologische Forschung5 219 – 272) who found the largest illusion (25%) at the optimal frequency for stroboscopic motion. Experiment 2 dealt with the effect of inversions (I), mirror reflections (M), and rotations (R) of the line during the stroboscopic movement (see Kolars and Pomerantz, 1971 Journal of Experimental Psychology87 99 – 108). The particular movements were signalled by means of a short horizontal line added to one end of each of the two vertical lines of experiment 1. The configurations were (1), signifying parallel motion in one plane; (2), locomotion with rotation around the vertical axis (M); (3), locomotion with rotation around the horizontal axis (I); and (4), locomotion with rotation in the plane of the display (R). In all these conditions, the shortening illusion was significantly larger than in experiment 1. The differences between the four conditions were not statistically significant, but the illusion under condition (1) seemed smaller than in the other three conditions. With SOAs for optimal stroboscopic motion, ‘rotation’ paths tended to appear three-dimensional.
The Phototactic Sensorimotor Mechanism of the Unicellular Alga Euglena Gracilis. An Application to the Evolutionary Study of Vision
Authors: Insinna E M 
Published: December 2015

Our understanding of even basic functions of microtubules (MT) such as intracellular transport and ciliary beating, including their role in sensory cells and nerve cells, is still incomplete. For example, vertebrate photoreceptors contain a cilium whose possible dynamical function is still unknown. A new model of microtubular dynamics, developed by me together with P Zaborski and J Tuszynski [Insinna et al, 1996 BioSystems39(3) 187 – 226], is capable of accounting for most of the phenomena associated with cell motility. Additionally, it sheds new light not only on the phototactic behaviour of the Protozoan Euglena gracilis but also on some possible evolutionary steps leading from primitive sensory organs to more complex ones such as the photoreceptors of vertebrates. Euglena displays simple perceptive functions (phototaxis) based on a primitive photoreceptor. This unicellular organism offers a unique possibility to study the function of MT in a simple form of vision. The model is based on classical nonlinear physics and suggests a dynamical role for MT in vertebrate photoreceptors. I am convinced that a better understanding of photoreceptor dynamics requires knowledge of the evolutionary steps leading to their development.
Visual Perception of Optic Flow in the Left and in the Right Visual Hemifield
Authors: Levashov O V , Levashova H 
Published: December 2015

Recently we have found right visual hemifield (HF) superiority in detection of local texture optic flow discontinuity (H O Levashova and O V Levashov, 1996 Perception25 Supplement, 128). In the present work we investigated a possible difference between hemifields in the perception of global optic flow. The stimulus consisted of two large texture fields which moved across the screen to the left and to the right from a central vertical line. It gave the illusion of motion through an infinite corridor with high walls. The left or the right wall could be curvilinear (convex) while the other one was flat. In order to make the task more difficult the central vertical meridian of the screen was occluded by a black mask with a width of 5 deg. The task of the subject was to detect the curvilinear wall and press the ‘left’ or the ‘right’ key in accordance with target position. When the target was absent (in some presentations both the walls were flat) or when the subject could not detect it he/she had to press the third key. The distance from the screen was 57 cm. One experimental session consisted of 100 – 150 trials. All subjects showed a superiority of the right hemifield (the difference was significant, p<0.05). The observed right-hemifield superiority in the detection of large texture flow could suggest that the left hemisphere has a certain dominance in visual perception of optic flow. This is in agreement with the hypothesis that the left hemisphere is more ‘phasic’ and the right hemisphere is more ‘tonic’ [O V Levashov, 1989 Computational Models of Sensory Systems (Moscow: VINITI) (in Russian)].
Masking Effects Induced by Perceptual Colour Components
Authors: Bedat L , Saadane A , Barba D 
Published: December 2015

Signals from the three types of cone photoreceptors are generally thought to be combined into two opponent-colour components and an achromatic component. Here we have chosen the cardinal directions Ach (achromatic axis), Cr1 (reddish - greenish axis) and Cr2 (bluish - yellowish axis) defined by Krauskopf to build a colour image coding scheme based on features of the human visual system. In order to design the optimal perceptual quantisers, we studied the perception of colour at different spatial frequencies, measuring the effect of a colour masking signal on the perception threshold for achromatic or chromatic sine-wave gratings. Three cases were considered to describe these interactions. First, we measured the masking effect of each colour component by itself. For the two chromatic components, we observed a pedestal effect for low masking contrasts and threshold rises for higher masking contrasts. Second, we studied interactions between the two colour axes. With colour masking signals composed of Cr1 and Cr2 components, thresholds for Cr1 stimuli dropped at low contrasts of the Cr2 component of the masking signal. This effect disappeared for high Cr2 masking contrasts. This was true at all contrasts of the Cr1 component of the masking signal. Thresholds for Cr2 stimuli were not modified by Cr1 masking. Finally, interactions between the chromatic and achromatic components were more complex. We observed a strong modification of the achromatic contrast-sensitivity function when a Cr1 masking sine-wave grating was added. When the achromatic frequency was lower than the colour masking frequency, the threshold rose. However, when the achromatic frequency was higher than the colour masking frequency, there was a significant pedestal effect. The global effect is a shift of the achromatic contrast sensitivity function. With a Cr2 masking signal, no significant modification of the achromatic contrast-sensitivity function was observed.
Noise Effects in Perceptual Models
Authors: Wickens T D , Olzak L A 
Published: December 2015

In studies of visual perception performance is often measured by statistics that are ratios of a perceptual magnitude to its intrinsic variability, most commonly the signal-detection measure d'=delta sigma. Many models for visual phenomena treat the variability sigma as a constant and describe performance exclusively by delta. However, in models for the combination of stimulus attributes, the combination process affects both terms, and an observed d' reflects both delta and sigma. For example, we have shown that masking and configural effects with sinusoidal plaids can be at least partially interpreted as noise effects. We have developed methods to analyse these effects. Through a series of concurrent-response experiments using grating stimuli, some reported at earlier ECVP meetings, we have measured the form and magnitude of the noise sources. Our analysis allows us to model the way that primitive Fourier components (spatial frequency by orientation) are integrated to form second-order or third-order combinations (eg spatial frequency pooled over orientation).
The Effects of Chromatic Conditions for Transparency
Authors: Ito Y , Uchikawa K 
Published: December 2015

When two rectangles overlap crosswise like a letter X, we perceive them as transparent in certain conditions. Perception of transparency is constrained by the luminance and chromatic relations of the overlapping and non-overlapping areas and the background, but not necessarily by their physical transmission profiles. In this study, we investigated the relation between luminance and chromatic mechanisms for the percept. Using two crossed rectangles (2 deg × 8 deg), we measured the ranges of chromaticity and luminance of the overlapping area (2 deg × 2 deg) that allowed the percept of transparent layers. We found that the ‘transparency’ luminance range was shifted by the intensity of the background. When the two rectangles were isochromatic and isoluminant (10 cd m−2) on a dark background, the overlapping area had to be around 0.3 log units brighter than the rectangles. When the background was D65 white (60 cd m−2), the luminance range for transparency was lower than the luminance of the rectangles. When the two rectangles differed in colour, however, the ‘transparency’ range of the overlapping area varied around the luminance of the rectangles. Transparency was perceived best when the colour of the overlapping area was on the additive mixture chromaticity line of the two rectangles. We discuss how the background influences the appearance of transparency and how the chromatic mechanism is effective in transparency.
Elementary Colour Perception in Hue Judgment
Authors: Sakata K 
Published: December 2015

The ratios of psychological elementary colours perceived in chromatic colour papers with a variety of hues were measured by a paired comparison method. Stimulus sets were composed of two colour papers with hues between two of four elementary colours, but on either side of one elementary colour. Five students observed stimulus sets comprising two colour papers under approximately 1000 lux D65 illumination, and they chose the one which caused the stronger elementary colour percept. The results showed that the sum of the ratios of two elementary colours in a colour whose hue is located between them was less than 100%. This result was the same for every hue condition. This shows that observers underestimated psychological elementary colours, consistent with previous studies (Sakata, 1996 Perception25 Supplement, 100) which showed that the sum of black and white was less than 100% in the perception of greys. If elementary colours are processed simultaneously from the whole colour percept, their sum would be 100%. The result of these experiments strongly shows that psychological elementary colours are processed independently from the inputs of the three cone systems and the rod system, and they are integrated to form the whole colour percept after each process.
From Simple to Complex or Vice Versa: Sequence Effects on the Detection of Embedded Figures
Authors: Ludwig I 
Published: December 2015

In a series of studies concerning part - whole perception we have investigated effects of perceptual learning, and of systematically varied presentation orders on the detection of embedded figures. In the present study the effects of increasing and decreasing complexity orders on detection performance are reported. Stimuli were 170 pairs of whole and part figures. Half of them were positive items, ie the searched part was contained in the (simultaneously presented) whole. The other half were negative items, ie the searched part was not contained in the whole. The difficulty of all figure pairs was determined from earlier data. On the basis of these difficulty parameters three presentation orders were created: (1) increasing difficulty (from simple to complex), (2) decreasing difficulty (from complex to simple), and (3) randomised order. Sixty subjects performed each of these tasks in three sessions separated by one week. Effects of practice and samples were balanced by permutating the order of the three tasks. The reaction times and error rates for all presentations were registered. The results showed marked differences between the three tasks: The lowest mean reaction time was obtained in the presentation order with increasing difficulty. Error rate, on the other hand, was lowest in the decreasing-difficulty presentation order. For the random-order presentation error rate and reaction time was in between the other orders. Furthermore, differences in benefit from practice were observed between the three orders of difficulty. Results are discussed with respect to the question of how efficient search strategies may be learned and whether one can learn to bend the rules of Gestalt organisation if required.
Neural Modelling of Disparity Influences in Optic-Flow Processing
Authors: Lappe M , Grigo A 
Published: December 2015

Last year, we reported a new disparity effect on optic-flow perception. It occurs when a flow field of radially moving random dots is transparently superimposed by a unidirectional motion pattern. Subjects asked to locate the centre of the expansion pattern perceive it shifted away from its true position (Duffy and Wurtz, 1993 Vision Research33 1481 – 1490). The magnitude of this shift depends on binocular disparity between the two superimposed patterns: presenting the translation in front of the expansion causes a massive reduction of the shift, presenting it behind the expansion yields only a slight reduction. To determine possible mechanisms for this interaction, we tried to model our results by modifying a previously developed neural model for optic-flow processing (Lappe and Rauschecker, 1995 Vision Research35 1619 – 1631). We compared three possible mechanisms of disparity influence. The first was based on the assumption that the absolute distance of the stimuli from the observer was known. The second was based on a disparity-based spatial integration, as found in ‘tuned’ neurons in primate visual area MT. Neither could account for our data. Finally we included a disparity-dependent weighting function in the model, assuming that distant flow vectors contribute more strongly than near ones to the processing of optic flow. This reproduced the experimental findings. Surprisingly, the optimal weighting function was similar to the disparity-dependence of the so-called ‘far-neurons’ in area MT. We conclude that the visual system uses disparity in optic-flow processing by putting special emphasis on distant flow vectors, and that far-neurons in MT might serve as a neuronal substrate for this.
Brightness Filling-in of Natural Images
Authors: Elder J H 
Published: December 2015

There is both psychophysical and physiological evidence that the perception of brightness variations in an image may be the result of a filling-in process in which the luminance signal is encoded only at image contours and is then neurally diffused to form representations of surface brightness. Despite this evidence, the filling-in hypothesis remains controversial. One problem is that in previous experiments highly simplified synthetic stimuli have been used; it is unclear whether brightness filling-in is feasible for complex natural images containing shading, shadows, and focal blur. To address this question, we present a computational model for brightness filling-in and results of experiments which test the model on a large and diverse set of natural images. The model is based on a scale-space method for edge detection which computes a contour code consisting of estimates of position, brightness, contrast, and blur at each edge point in an image (Elder and Zucker, 1996, paper presented at ECCV). This representation is then inverted by a diffusion-based filling-in algorithm which reconstructs an estimate of the original image. Psychophysical assessment of results shows that while filling-in of brightness alone leads to significant artifact, parallel filling-in of both brightness and blur produces perceptually accurate reconstructions. The temporal dynamics of blur reconstruction predicted by the model are consistent with psychophysical studies of blur perception (Westheimer, 1991 Journal of the Optical Society of America A8 681 – 685). These results suggest that a scale-adaptive contour representation can in principle capture the information needed for the perceptually accurate filling-in of complex natural images.
Perceived Stability of a Scene Depending on the Gain of Motion Parallax
Authors: Runde D , Ruschin D , Feddersen E 
Published: December 2015

An observer moving in a natural environment is usually able to separate the constant changes of his retinal images in such a way that he perceives the environment and the changes of his observation point independently. The necessary and sufficient conditions to perceive a stable environment in spite of the retinal change produced by self-motion are, however, as yet unknown. We found that under certain conditions a scene that changes during observer motion can appear more stable than a rigid one. In our experiment a scene consisting of a number of LEDs distributed in a dark room was visible through a window. A mechanical device controlled by a head-tracker was used to move the LEDs during head motion to either reduce or enhance motion parallax by a predefined gain factor. The subjects rated the scene with respect to different attributes including apparent deformation and degree of motion perceived. They were also asked to adjust the parallax gain to the value of greatest apparent stability of the scene. Monocular as well as binocular trials were conducted and different fixation points were employed. The result was a general tendency in all conditions to perceive scene motion when the scene was in fact rigid and to perceive the greatest stability when the scene was distorted in such a way as to produce reduced motion parallax.
Non-Linear Interactions in Cortical Responses to Bilateral vs Unilateral Visual Field Stimulation
Authors: Ahlfors S P , Foxe J J , Ilmoniemi R J , Simpson G V 
Published: December 2015

Stimuli in different parts of the visual field can be perceived as independent entities and as conjoined wholes. It is of interest to determine whether there are cortical representations of the left and right hemifields which remain as independent entities when both hemifields are stimulated simultaneously and/or whether they interact to form a conjoined representation. We examined whether cortical processing of visual stimuli depends on whether they occur in isolation in one hemifield (unilaterally) or simultaneously in both hemifields (bilaterally). Visual evoked potentials of six normal subjects were recorded from 128 scalp sites. Wedge-shaped chequerboard stimuli, extending 1 – 4 deg eccentricity, were presented to quadrants of the visual field. Stimulus duration was 250 ms; the stimulus onset asynchrony was random, 500 – 750 ms. The evoked potentials revealed multiple peaks of activity with different surface topography. Prominent deflections occurred around 80, 120 – 180, and 230 ms. The response to bilateral stimuli was compared with the sum of the responses to unilateral stimuli. On the basis of the multichannel recordings, nonlinear interactions were characterised as either (a) modulations (same generators, but different amplitude) or (b) interactions originating from different generators. Modulation occurred at 230 ms, the response being suppressed for the bilateral case. At 120 – 180 ms, the field patterns suggested that at least some of the sources of the interaction effect are different from the source of the bilateral response. Underlying generators of the evoked responses and the interaction effects were further explored with the use of an equivalent current dipole model.
Continuous Assessment of Presence in Stereoscopic Displays
Authors: IJsselsteijn W A , Freeman J , Avons S E , Davidoff J , de Ridder H , Hamberg R 
Published: December 2015

Presence, a sense of ‘being there’ evoked by a display, can be regarded as a concept of central importance in the evaluation of broadcasting and entertainment services in general and virtual reality applications in particular. Subjective methods of assessing presence that have either been used or proposed to date do not provide a measure of temporal variation in observers' presence. To overcome this limitation, we have applied the method of continuous assessment (ITU-R, BT 500-7) to the measurement of presence. Thirty observers (twelve at IPO, eighteen at UoE) with normal or corrected-to-normal vision and good stereo-acuity viewed a stereoscopic film. While watching, observers were asked to continuously rate their perceptions of depth, naturalness and presence. The stimulus material varied considerably in the amount and strength of the visual cues presented over time. This enabled us to investigate whether the extent of sensory information presented to an observer was a determinant of presence, as proposed by Sheridan [1992 Presence: Teleoperators and Virtual Environments1(1) 120 – 125]. The results, which were very similar across two independent laboratories, suggested that continuous assessment provides a promising methodology for the subjective assessment of temporal variation in the observer's sense of presence. Further, increasing the extent of sensory information presented to an observer may enhance the sense of presence, provided the depth cues introduced are consistent and within natural bounds. [ Note: First and second author in arbitrary order.]