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S Shimojo

Publications and source records attributed to S Shimojo.

At least 37 records · Page 2Linked to original sources
PubMed1996

Location vs feature: reaction time reveals dissociation between two visual functions.

Reaction time in a detection or a location discrimination task was longer when a target appeared at the same location as in the previous trial (inhibition of return; IOR). However, it became shorter when the task was color or orientation discrimination (facilitation of return: FOR). This dichotomy was observed in the single target as well as in the popout displays. In additional experiments, vernier, size, and luminance discriminations all led to FOR, whereas eye-movement and arm-reaching tasks led to IOR. Moreover, identical stimuli could lead to the opposite patterns of result depending on the nature of the task: inhibition in global location tasks, and facilitation in feature analysis tasks. These may correspond to "where" vs "what" or "action" vs "recognition" pathways neurophysiologically.

Analysis of Variance↗
PubMed1996

Assimilation-type and contrast-type bias of motion induced by the surround in a random-dot display: evidence for center-surround antagonism.

As a mechanism to detect differential motion, we have proposed a model of "a motion contrast detector" that has a center-surround antagonistic receptive field with respect to the direction of motion. Supporting evidence has been obtained in the studies of induced motion, motion capture, and motion aftereffect. In order to obtain further evidence in a more strictly controlled situation, we examined the perceptual bias of motion in a center stimulus induced by another, surrounding motion. By using a stochastic random-dot display configured in a center-surround concentric fashion, we measured the % signal in the center stimulus that made the stimulus perceptually stationary in the presence of a moving surround. Measurements were done for various stimulus sizes and eccentricities. The amount of bias changed as a function of stimulus size and eccentricity. At several eccentricities, smaller stimulus sizes tended to yield assimilation-type biases, whereas larger sizes tended to yield contrast-type biases. However, a spatial scaling procedure revealed that the amount of bias was a simpler function of "scaled" stimulus size that was obtained by dividing the physical size by a scaling factor at each eccentricity. In the scaled profile, assimilation-type bias changed to contrast-type bias with increasing size, reached the peak of contrast-type bias at a certain size, and decreased slightly with further increasing size. Furthermore, a model of a difference of Gaussians, DOG, function well approximated the behavior of the profile. From these results, we concluded that the process specific to perceiving relative motion is mediated by a motion contrast detector, which is possibly located in area MT.

Humans↗
PubMed1996

Orienting a 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.

Adaptation, Physiological↗
PubMed1996

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.

Attention↗
PubMed1996

'Generic-view principle' for three-dimensional-motion perception: optics and inverse optics of a moving straight bar.

The generic-view principle (GVP) states that given a 2-D image the visual system interprets it as a generic view of a 3-D scene when possible. The GVP was applied to 3-D-motion perception to show how the visual system decomposes retinal image motion into three components of 3-D motion: stretch/shrinkage, rotation, and translation. First, the optical process of retinal image motion was analyzed, and predictions were made based on the GVP in the inverse-optical process. Then experiments were conducted in which the subject judged perception of stretch/shrinkage, rotation in depth, and translation in depth for a moving bar stimulus. Retinal-image parameters-2-D stretch/shrinkage, 2-D rotation, and 2-D translation-were manipulated categorically and exhaustively. The results were highly consistent with the predictions. The GVP seems to offer a broad and general framework for understanding the ambiguity-solving process in motion perception. Its relationship to other constraints such as that of rigidity is discussed.

Bayes Theorem↗
PubMed1995

Modulation of motion aftereffect by surround motion and its dependence on stimulus size and eccentricity.

As a mechanism to detect differential motion, we have proposed a model of 'a motion contrast detector' and have shown that it can explain the perceptual change from motion capture to induced motion with increasing stimulus size and decreasing eccentricity. To further test the feasibility of the model, we examined the effect of surround motion on the motion aftereffect (MAE) elicited in the center. Using a drifting grating surrounded by another drifting grating, the duration of MAE in the center after adaptation was measured for various surround velocities (Expt 1). MAE was stronger when the surround moved oppositely to, than together with, the center. This finding was consistent with some previous reports. Using similar stimuli, MAE was measured at various stimulus sizes and eccentricities by the cancellation technique (Expt 2). The effect of surround modulation turned out to vary with both size and eccentricity. We examined if the apparent dependence on eccentricity could reflect a simpler effect of cortical size when the data were rescaled according to a linear scaling factor. We interpret our results in terms of motion contrast detectors, possibly located in the area MT.

Adaptation, Ocular↗
PubMed1995

The locus of visual-motor learning at the task or manipulator level: implications from intermanual transfer.

To assess the functional locus of visual-motor learning, the computational concepts of "task level" programming (determination of the trajectory of a hand during arm reaching in the Cartesian coordinates) and "manipulator level" programming (determination of the joint coordinates) was adopted. Because the former is likely to be hand nonspecific and the latter is hand specific, it is assumed that learning at the task level should be transferred to the unpracticed hand, whereas that at the manipulator level it should not. Under this assumption, the paradigm of intermanual transfer was used in an aiming task under rotated visual feedback. Nearly 100% intermanual transfer from the practiced hand to the unpracticed hand in the performance time of aiming was found, concluding that the locus of visual-motor learning should be at the task level rather than at the manipulator level.

Adolescent↗
PubMed1995

The theory of the curvature-constraint line for amodal completion.

Amodal completion of partly occluded figures is analyzed as natural computation. Here amodal completion is shown to consist of four subproblems: representation, parsing, correspondence, and interpolation. Second, each problem is shown to be basically solvable on the basis of the generic-viewpoint assumption. It is also argued that the interpolation problem might be the key problem because of mutual interdependence among the subproblems. Third, a theory is described for the interpolation problem, in which the generic-viewpoint assumption and the curvature-consistency assumption are presumed. The generic-viewpoint assumption entails that the orientation and the curvature should not change at the point of occlusion. The curvature-consistency assumption entails that the hidden contour should have the minimum number of inflections to maintain continuity in orientation and curvature. The shape of the interpolated contour represented qualitatively in terms of the number of inflections can uniquely be determined when the location of the terminators and local orientation and curvature of the visible contours at the terminators are given. Fourth, it is shown in an instant psychophysics that the theory is highly consistent with human performance.

Adult↗
PubMed1994

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.

Depth Perception↗
PubMed1993

Motion capture changes to induced motion at higher luminance contrasts, smaller eccentricities, and larger inducer sizes.

In the stimulus configuration for "motion capture" phenomenon, we varied luminance contrast of the center disk (target), eccentricity and stimulus size. The subjects had to judge the direction of perceived target motion. We found that motion capture changed to induced motion (the direction of illusory motion was reversed) at smaller eccentricities and larger stimulus sizes. At intermediate eccentricities, motion capture changed to induced motion with increasing luminance contrast of the target. By using magnitude estimation, we also found that even a luminance-defined target was captured ("homochromatic motion capture") and that a moving target was captured by a stationary inducer ("position capture"). Both motion and position capture effects were commonly observed at lower luminance contrasts of the target, larger eccentricities and smaller sizes. From these results, we propose a model of center-surround antagonistic motion contrast detectors in motion processing.

Contrast Sensitivity↗
PubMed1993

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.

Attention↗
PubMed1993

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.

Animals↗
PubMed1993

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.

Adult↗
PubMed1992

Experiencing and perceiving visual surfaces.

A theoretical framework is proposed to understand binocular visual surface perception based on the idea of a mobile observer sampling images from random vantage points in space. Application of the generic sampling principle indicates that the visual system acts as if it were viewing surface layouts from generic not accidental vantage points. Through the observer's experience of optical sampling, which can be characterized geometrically, the visual system makes associative connections between images and surfaces, passively internalizing the conditional probabilities of image sampling from surfaces. This in turn enables the visual system to determine which surface a given image most strongly indicates. Thus, visual surface perception can be considered as inverse ecological optics based on learning through ecological optics. As such, it is formally equivalent to a degenerate form of Bayesian inference where prior probabilities are neglected.

Depth Perception↗
PubMed1992

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.

Attention↗
PubMed1992

Neon flank and illusory contour: interaction between the two processes leads to color filling-in.

Two aspects of neon color spreading, local color spreading (neon flank) and illusory contour, were investigated by dichoptic viewing. Neon flank was not observed under appropriate dichoptic stimulation, suggesting that input to the process for local color spreading is based on monocular configuration. However, illusory contours were formed according to the interocularly combined configuration rather than according to each monocular configuration, suggesting that input to the process responsible for illusory contours should be ocularly-nonselective and binocular, rather than monocular. The possibilities of artifacts such as those arising from interocular rivalry were appropriately eliminated, and thus, it is tentatively concluded that the process underlying local color spreading is monocularly driven, whereas the process underlying illusory contours is binocularly driven. Furthermore, a new demonstration is presented that indicates that interocularly-induced illusory contours 'capture' and extend the monocularly-induced local color spreading, resulting in global color spreading (neon color spreading). These results support our hypotheses that neon color spreading involves two separable processes in the early visual processing, the feature detection process (for local color spreading) and the illusory contour process, and that these two processes interact with each other at later stages of cortical processing. The relation of local color spreading and illusory contours to surface separation is also discussed.

Adult↗