The effect of sound on visual apparent movement

Twelve subjects found the longest possible interstimulus interval (ISI) at which they perceived continuous apparent motion of one light instead of partial motion or succession between two lights. In the visual condition, two lights only were presented. In the bimodal conditions, binaurally presented tones were presented synchronously with the lights, and the lights and tones were either spatially congruent (in phase) or incongruent (180 degrees out of phase). Bimodal presentations lowered the upper ISI threshold for the perception of visual apparent motion, and the reduction was greater when the tones and lights were spatially congruent. The threshold reduction may be caused by a perceptual inference about localization of the lights in space or by a change in visual persistence.     

Light and dark adaptation of visually perceived eye level controlled by visual pitch

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level averages approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30° topbackward or 20° topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.     

Effects of a visual frame and of low radial accelerations on the visually perceived eye level

The purpose of this study was to determine how the combined effects of a reference frame and of very low gravito-inertial forces produced by centrifugation affect the visually perceived eye level (VPEL). Twenty subjects were instructed to set a luminous target to the VPEL under various experimental conditions involving two main factors: (1) visual context (frameless, frame centered, frame moved down 50 mm, and frame moved up 50 mm) and (2) gravito-inertial context (motionless, Gi₁=9.81001 m/sec² and Gi₂ = 9.95 m/sec²). The visual context significantly reduced the lowering of VPEL in darkness as caused by radial acceleration; this confirms the prevailing role of vision versus propriosomesthesis. However, under condition Gi₂, there was a significant effect on the VPEL in spite of the presence of the luminous frame; this demonstrates that VPEL processing involves both visual and propriosomesthesic information. Furthermore, the VPEL varied linearly with the vertical shift of the luminous frame for any of the gravito-inertial conditions used in this study, but, under condition Gi₂, the VPEL was shifted downward.     

Topological aspects of apparent visual motion

Summary and Conclusions Linke's pioneer observations made just fifty years ago on apparent visual motion conditioned by pairs of stimulus objects which differ in form, has been here experimentally elaborated and brought into relation with topology. Both deformations and connectivities have been studied. Topological limits of t-motion have been encountered in this investigation. Linke's concept of identity, which he regarded as the psychological key to seen movement, should now be replaced by the modern, powerful concept of invariance. Topology, with its biunique point-order structure, is inevitably brought into relation with the phenomena of apparent movement. There appears to be a substantial isomorphic relation between topological deformation in the stimulus objects and seen movement, although there are some topological inhibitors of motion. The perceptual contents of apparent motion do not evidence positional and form properties as separated parts: The contents are funded as an integrated kinematic whole.     

Overshoot of curvature in visual apparent motion

If a curved line and a straight line are presented briefly, one above the other, in sequence to the eye, then, under appropriate conditions, visual apparent motion is obtained. Subjects report that the illusory figure moving and changing from the curved line to the straight line appears to overshoot the latter, gaining a small curvature in the opposite sense. Three experiments are described. In the first, the magnitude of this apparent curvature was quantified as a function of the delay between the onsets of the curved line and straight line (the stimulus onset asynchrony, SOA). It is shown that overshoot in curvature cannot be attributed to inappropriate patterns of eye fixations. In the second experiment, the stimulus configuration was modified to reveal the contribution to apparent curvature of classical curvature-contrast effects. Curvature overshoot due to apparent motion alone was thus estimated as a function of SOA. In the third experiment, an analogous position overshoot was measured for apparent motion elicited by two brief sequentially presented parallel line segments. It is argued that a combination of such position overshoots cannot explain curvature overshoot. Two schemes of a more general kind that might be used to interpret curvature overshoot are then outlined. One scheme is based on a neural-net model of apparent motion, and the other on a functional model of apparent motion that operates by laws analogous to those governing real physical motion.     

The effect of brief auditory stimuli on visual apparent motion

When two discrete stimuli are presented in rapid succession, observers typically report a movement of the lead stimulus toward the lag stimulus. The object of this study was to investigate crossmodal effects of irrelevant sounds on this illusion of visual apparent motion. Observers were presented with two visual stimuli that were temporally separated by interstimulus onset intervals from 0 to 350 ms. After each trial, observers classified their impression of the stimuli using a categorisation system. The presentation of short sounds intervening between the visual stimuli facilitated the impression of apparent motion relative to baseline (visual stimuli without sounds), whereas sounds presented before the first and after the second visual stimulus as well as simultaneously presented sounds reduced the motion impression. The results demonstrate an effect of the temporal structure of irrelevant sounds on visual apparent motion that is discussed in light of a related multisensory phenomenon, 'temporal ventriloquism', on the assumption that sounds can attract lights in the temporal dimension.     

Detecting eye movements in dynamic environments

To take advantage of the increasing number of in-vehicle devices, automobile drivers must divide their attention between primary (driving) and secondary (operating in-vehicle device) tasks. In dynamic environments such as driving, however, it is not easy to identify and quantify how a driver focuses on the various tasks he/she is simultaneously engaged in, including the distracting tasks. Measures derived from the driver’s scan path have been used as correlates of driver attention. This article presents a methodology for analyzing eye positions, which are discrete samples of a subject’s scan path, in order to categorize driver eye movements. Previous methods of analyzing eye positions recorded in a dynamic environment have relied completely on the manual identification of the focus of visual attention from a point of regard superimposed on a video of a recorded scene, failing to utilize information regarding movement structure in the raw recorded eye positions. Although effective, these methods are too time consuming to be easily used when the large data sets that would be required to identify subtle differences between drivers, under different road conditions, and with different levels of distraction are processed. The aim of the methods presented in this article are to extend the degree of automation in the processing of eye movement data by proposing a methodology for eye movement analysis that extends automated fixation identification to include smooth and saccadic movements. By identifying eye movements in the recorded eye positions, a method of reducing the analysis of scene video to a finite search space is presented. The implementation of a software tool for the eye movement analysis is described, including an example from an on-road test-driving sample.     

Visually perceived eye level: changes induced by a pitched-from-vertical 2-line visual field.

The physical elevation corresponding to visually perceived eye level (VPEL) changes linearly with the pitch of a visual field. Deviations from true eye level average more than 0.5 times the angle of pitch over a 65 degrees pitch range. A visual field consisting of 2 dim, isolated vertical lines in darkness is more than 4/5 as effective as that of a complexly structured visual field; 2 horizontal lines have a small and inconsistent effect. Differences in influence on VPEL between pitched-from-vertical and horizontal lines were predicted from an analysis that extracted differences in retinal perspective resulting from changes in pitch. The Great Circle Model (GCM), based on a spherical approximation to the erect, stationary eye, predicts the present results and results of 8 other sets of experiments. The model treats the influence of a single line on VPEL as systematically related to the elevation of the intersection between the great circle containing the image of the line and the central vertical retinal meridian; generalized GCM combines visual inputs with inputs from the body-referenced mechanism and maps onto the central nervous system.     

Effect of level of confusability on reporting letters from briefly presented visual displays

In a report paradigm, two letters are presented on a trial which are either confusable(e.g., P and R) or nonconfusable (e.g., P and M) in terms of visual features. Across trials, interletter distance, retinal location, duration, and visual field are varied. Identification accuracy on confusable trials was generally lower than on nonconfusable trials, and this effect of level of confusability increased with distance from the fixation point, decreased with duration, and was smaller on the central letter than on the more peripheral letter. A quantitative model, incorporating aspects of the interactive channels model (Estes, 1972) and feature perturbation model (Wolford, 1975), is developed and tested. One parameter of the model measures the effective similarity between two letters after lateral inhibition has occurred, and other parameters measure the probability of feature perturbation in foveal and peripheral directions.     

The influence of eye movements and eye position on perception of the visual vertical

Summary Four experiments are reported which involved the adjustment of two points of light in an otherwise dark room to the visual vertical. In the first two experiments different point separations (corresponding to visual angles of about 2° and 23°) were employed in an attempt to control the degree of scanning eye movements. Binocular adjustments to the visual vertical during body tilt were influenced by the point separation (Exp. 1), but monocular adjustments with the head upright were not (Exp. 2). Using the larger point separation and fixating the top point the visual vertical using the right eye was counterclockwise of that with fixation of the bottom point when the head was upright (Exp. 3), but this difference was not found for judgments during tilt (Exp. 4). The results were discussed in terms of the rotational changes in eye position accompanying scanning eye movements and ocular elevation and depression.

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Zusammenfassung Es wird über vier Experimente berichtet, in denen es um die Einstellungen zweier Lichtpunkte in eine vertikale Richtung geht. In den ersten zwei Experimenten sollte der Einfluß der Fixierbewegungen der Augen geprüft werden. Der Winkelabstand der Lichtpunkte betrug 2° oder 23°. Bei seitwärts geneigtem Körper und binokularer Betrachtung wurde ein Unterschied gefunden (Exp. 1). Bei aufrecht gehaltenem Kopf und monokularer Betrachtung dagegen zeigte sich kein Unterschied (Exp. 2). Wurde in aufrechter Körperlage und bei einem Punktabstand von 23° der obere Punkt mit dem rechten Auge fixiert, so verschob sich die scheinbare Vertikale im Uhrzeigersinn; sie verschob sich noch weiter im Uhrzeigersinn, wenn der untere Punkt fixiert wurde (Exp. 3). Bei geneigtem Körper wurde dagegen kein Unterschied festgestellt (Exp. 4). Die Ergebnisse werden im Zusammenhang mit der Augendrehung diskutiert, die mit dem scanning sowie mit der Auf- und Abbewegung der Augen beim Fixieren verbunden ist.

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This research was carried out while I was a recipient of a Forschungsstipendium from the Alexander von Humboldt-Stiftung, appreciation for which is gratefully acknowledged. I also wish to thank the subjects who participated in the experiments.     

Effects of living in the up-down inverted visual world on apparent movement

The purpose of this study was to examine whether a change of perceptual framework may affect the occurrence of apparent movement. Apparent movement was observed by one subject living over four days in the prismatically inverted visual world, because this situation was considered as the operation in which the subject was forced to change the perceptual framework to adapt himself to the novel environment. Apparent movement with two points was measured in vertical and horizontal configurations before wearing and after removing the prism as well as while wearing it. Analysis showed significant effects of prism-wearing on the occurrence of apparent movement in both vertical and horizontal configurations. Although further elaboration is required, an hypothesis was suggested from the viewpoint of the loss of visual position constancy.     

Dynamic visual capture: apparent auditory motion induced by a moving visual target

Apparent motion of a sound source can be induced by a moving visual target. The direction of the perceived motion of the sound source is the same as that of the visual target, but the subjective velocity of the sound source is 25-50% of that of the visual target measured under the same conditions. Eye tracking of the light target tends to enhance the apparent motion of the sound, but is not a prerequisite for its occurrence. The findings are discussed in connection with the 'visual capture' or 'ventriloquism' effect.     

Effect of grammatical gender on visual word recognition: evidence from lexical decision and eye movement experiments

Lexical decision times and eye movements were recorded to determine whether grammatical gender can influence the visual recognition of isolated French nouns. This issue was investigated by assessing the use of two types of regularities between a noun's form and its gender--namely ending-to-gender regularities (e.g., the final letter sequence -at appears only in masculine nouns and, thus, is predictive of masculine gender) and gender-to-ending regularities (e.g., feminine gender would predict the final letter e, whereas masculine gender would not). Previous studies have shown that noun endings are used by readers when they have to identify gender. However, the influence of ending-to-gender predictiveness has never been investigated in a lexical decision task, and the effect of gender-to-ending regularities has never been evaluated at all. The results suggest that gender information can influence both the activation stage (Experiments 1 and 3) and the selection stage (Experiments 2 and 3) of the word recognition process.