Shinsuke Shimojo

Focal visual attention produces illusory temporal order and motion sensation

Spatial attention was studied using a new visual illusion of motion: a line, which was presented physically at once, was perceived to be drawn from one side when attention had been captured to that side of the line by a preceding visual cue stimulus. By comparing with a temporal order task, we showed that the line-motion illusion was produced by acceleration of visual information processing at the locus of attention. The results suggest that the facilitatory effect of attention is exerted at relatively early stages of visual information processing where visual signals are to be fed into the motion detecting mechanism.

Voluntary and stimulus-induced attention detected as motion sensation

Attention may be drawn passively to a visually salient object. We may also actively direct attention to an object of interest. Do the two kinds of attention, passive and active, interact and jointly influence visual information processing at some neural level? What happens if the passive and active attentions come into conflict? These questions were addressed with the aid of a novel psychophysical technique which reveals an attentional gradient as a sensation of motion in a line which is presented instantaneously. The subjects were asked to direct attention with voluntary effort: to the side opposite to a stimulus change, to an object with a predetermined colour, and to an object moving smoothly. In every case the same motion sensation was induced in the line from the attended side to the unattended side. This voluntary attention, however, can easily and quickly be distracted by a change in the periphery, though it can be regained within a period of 200 to 500 ms. The results suggest that the line motion can be induced in voluntary (top-down) as well as stimulus-driven (bottom-up) situations, thus indicating the truly attentional nature of the effect, rather than it being some kind of retinotopic sensory artifact or response bias. The results also suggest that these two kinds of attention have facilitatory effects acting together on a relatively early stage of visual information processing.

Infants' fast saccades in the gap paradigm and development of visual attention☆

Abstract The saccadic reaction times (SRTs) in the overlap, no-overlap, and gap conditions of 2.5- to 12-month-old infants and adults were measured. In the overlap condition, the SRTs of younger infants were over 600 ms longer than those of older infants, whereas the SRTs in the gap condition of the younger infants were 300–350 ms, much faster than reported hitherto, and were shortened only by about 100 ms. The results indicate that the oculo-motor system and attention process for disengagement in the gap condition mature earlier than the attention process for disengagement in the overlap condition.

Visual attention revealed by an illusion of motion

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. A new psychophysical method using an illusion of motion perception allowed us to visualize the field of the magnitude of attention and its dynamic changes. Based on our experiments using this method we suggest that (1) both passive (bottom-up) and active (top-down) attention exert their effects on the early stages of visual processing, (2) active attention can quickly and briefly be replaced by passive attention induced by an external event, but can be restored in about 400 ms, and (3) attention is directed to an object, not space, and follows the object as it moves.

Orienting of spatial attention – its reflexive, compensatory, and voluntary mechanisms

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion--line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side when attention was captured to that side of the line by a preceding visual cue stimulus. This effect was due to acceleration of visual information processing at the locus of attention. The motion illusion was produced by both stimulus-induced (bottom-up) and voluntary (top-down) attention, which suggested that the two kinds of attention act on relatively early stages of visual processing. The objective of this study was to examine how various modes of spatial attention might be represented and reorganized in the brain. Using the induction of illusory line motion as a measure we found that: (1) once attention is captured by a moving object, it follows the object as it moves; and (2) attention moves with a saccade in the retinal coordinates such that its focus remains fixed in space. We then asked whether attention acts across different sensory modalities. We found that both auditory and somatosensory cues induced focal visual attention in space where the cue was presented. Based on these findings we propose a model which would allow (1) matching of visual spatial information obtained across saccades, and (2) matching of spatial information obtained in different sensory modalities.

Illusory Occluding Contours and Surface Formation by Depth Propagation

A novel kind of depth-spreading effect which should be distinguished in various aspects from the known interpolation, averaging, or ‘filling-in’ phenomena is reported. The demonstrations and experiments suggest that depth from an uncrossed disparity can be extrapolated from, not just interpolated between, illusory or real contours to form perceptually a background surface. In addition, the form of the illusory contour itself could be drastically changed in configuration and sharpness, contingently with perceptual background-surface formation. No such effects of surface and contour formation were observed in the crossed disparity case. Because the illusory contours were enhanced and perceived as illusory ‘occluding contours’, these effects may be closely related to the ‘occlusion constraints’ in the real world.

Interocularly unpaired zones escape local binocular matching

When a closer surface partially occludes a more distant surface, there exist image zones adjacent to the occluding edge on the rear surface which are visible to one eye and not the other. These half-occluded or interocularly unpaired zones do not carry explicit disparity information, yet their depth is perceived as a stable and continuous extension of the rear surface. Moreover, such zones escape binocular rivalry. In addition to these properties, we now report another special characteristic of this unpaired zone in comparison to normally paired regions. An unpaired probe dot added here escapes non-unique local Panum matching which would otherwise bestow it with a depth outside the surface. Thus paradoxically, depth of the probe is most stable in the unpaired zone. This finding indicates that what is considered to be one of the most fundamental processes for binocular depth perception, namely local matching, is subject to more global surface occlusion constraints.

Adaptation to the Reversal of Binocular Depth Cues: Effects of Wearing Left-Right Reversing Spectacles on Stereoscopic Depth Perception

The principle of stereopsis, that crossed disparity causes a convex perception and uncrossed disparity a concave one, has for a long time been considered to depend on a very rigid neural mechanism not affected by experience. Experiments are reported here which show that this relationship between disparity and perceived depth can be reversed by experience. An observer wore a pair of left-right reversing spectacles continuously for nine days. The spectacles also reversed the relation between the direction of perceived depth and the direction of binocular depth cues, ie disparity and vergence. For a period starting two days before wearing the spectacles and continuing until seventy-nine days after their removal the observer was examined with a haploscope and an electrooculograph. All the stereoscopic experiments were carried out without spectacles in order to examine some aftereffects of wearing spectacles. For the stereograms with linear contours not only the adaptive reversal of the relation between disparity and perceived depth, but also some abnormal depth perceptions and long-lasting aftereffects were found. For Juleszs random-dot stereograms, however, in which contours can be seen only after binocular combination, no adaptive change or reversal occurred. These results suggest that the process of stereopsis consists of two concurrent subprocesses.

On the Perception of Two Successive Sound Bursts

SummaryThis paper is concerned with both time perception and the methodology of perceptual psychology. The perception of the pattern of two successive sound bursts was studied by two different methods, i.e., magnitude estimation and phenomenal report. The temporal interval between the bursts was varied from 38 ms to 3394 ms. First, the observer estimated the duration or speed of each pair by a number without modulus. The estimations could not be fitted by a single power function across the entire range of intervals. That is, the exponent changed discontinuously. Next, the observer categorized freely the impressions of all the pairs. The quality of the phenomenon changed at the point where the exponent changed. All the observers arrived at the same three categories expressing the phenomena of the pairs. The boundaries between them corresponded approximately to the intervals of 150 ms and 2000 ms. The pairs in the middle category were often associated with body movements. The other categories also are of a unique nature. Finally, the possibility and the usefulness of employing psychophysical methods and phenomenological methods together is discussed.

Stimulus-driven facilitation and inhibition of visual information processing in environmental and retinotopic representations of space

This contribution deals with two major issues on visual/spatial attention. One is the issue of facilitation and inhibition; that is, under what conditions facilitatory modulation occurs, and under what other conditions inhibitory modulation occurs. The other issue is that of spatial representation; in what type of spatial representation do these modulations occur, retinotopic or environmental? In the first half of this article, We review the latest studies employing various psychophysical measures to assess spatially-selective modulation of visual information processing. We also summarize our latest results on reaction time, indicating a dissociation of two visual functions, detection/orientation and feature discrimination. Based on these chunks of knowledge, we raise a questions about the spatial coordinate system in which the facilitatory and/or inhibitory modulations occur. We then provide results of two reaction-time experiments which partly answer the question.