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S Shimojo

Publications and source records attributed to S Shimojo.

At least 19 recordsLinked to original sources
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↗
PubMed1991

Mirror-reversal phenomena in the cutaneous perception and writing of children.

When a letter is drawn on the forehead, it is perceived cutaneously as a mirror reversal of the experimenter-defined stimulus. An analogous mirror-reversal phenomenon is found in motor behaviour; eg, writing on the downward-facing horizontal surface of a table. We examined these mirror-reversal phenomena in tasks, performed by 4-year-old and 8-year-old children, involving cutaneous perception and motor-production. The children's tendencies toward mirror reversal in the two tasks varied with the orientation and position of the surface, but were similar to those of sighted and blind adult subjects. In addition, mirror reversal was independent of the left-right indifference often observed in young children in writing or visual-matching tasks. The implications of these findings are discussed in the context of a body schema used to guide sensorimotor functions.

Attention↗
PubMed1990

Real world occlusion constraints and binocular rivalry.

A surface occluding a more distant surface gives rise to interocularly unpaired regions to its immediate left and right. The unpaired region on the left side is visible only to the left eye, whereas that on the right side is visible only to the right eye. Thus for real world scenes there are opto-geometrical constraints which determine whether particular combinations of relative depth and right-eye-only or left-eye-only stimuli are ecologically valid or invalid. We report a demonstration and experiments to show that opto-geometrically "valid" unpaired regions are seen as continuous with the rear plane and escape interocular suppression, whereas "invalid" unpaired regions are perceived as closer and are suppressed vigorously. An additional experiment indicates that the results cannot be understood in terms of correspondence solving, but require neural mechanisms that embody real-world occlusion constraints. These results suggest a rather close interaction between stereopsis and rivalry "modules". Since explicit eye-of-origin information is lost relatively early in the hierarchical organization of cortical visual processing, we argue that occlusion-related constraints must be embodied at such early levels.

Chi-Square Distribution↗
PubMed1990

da Vinci stereopsis: depth and subjective occluding contours from unpaired image points.

Distant surfaces are occluded by nearer surfaces to different extents in the two eyes, leading to the existence of unpaired image points visible in one eye and not the other. An ecological analysis of the real world situation that could have given rise to such unpaired points indicates the presence of a depth constraint zone, defined by visibility lines between which possible real world points must lie. The leading edge of this zone starts at the edge of a fused binocular occluding surface and recedes linearly with increases in horizontal distance to the unpaired point. Psychophysical evidence indicates that the human visual system makes use of this unpaired information in a remarkably adaptive manner, showing an increase in perceived depth for increasing horizontal separations between the unpaired target and fused edge, at least over a significant angular range (approx. 25-40 min arc). We also show that unpaired points in binocular images can lead to the formation of subjective occluding contours and surface having the qualitatively appropriate sign of depth. Furthermore, we show that the visual system could not recover depth of unpaired points camouflaged from the other eye against silhouettes. Our findings indicate that the visual system makes use of occlusive relations in the real world to recover depth, contour, and surface from unpaired points. The fact that such processes must utilize eye-of-origin information implies that they share this essential characteristic with classical or Wheatstone stereopsis. The necessity of eye-of-origin information also suggests that the processing may begin relatively early in cortical visual processing, possibly as early as V1. Finally, the novel emergence of subjective occluding contours from unpaired monocular stimuli raises the possibility that this process is mediated by visual experience, built up by the association of unpaired points and occluding contours.

Depth Perception↗
PubMed1990

Amodal representation of occluded surfaces: role of invisible stimuli in apparent motion correspondence.

A series of demonstrations were created where the perceived depth of targets was controlled by stereoscopic disparity. A closer object (a cloud) was made to jump back and forth horizontally, partially occluding a farther object (a full moon). The more distant moon appeared stationary even though the unoccluded portion of it, a crescent, changed position. Reversal of the relative depth of the moon and cloud gave a totally different percept: the crescent appeared to flip back and forth in the front depth plane. Thus, the otherwise-robust apparent motion of the moon crescents was completely abolished in the cloud-closer case alone. This motion-blocking effect is attributed to the 'amodal presence' of the occluded surface continuing behind the occluding surface. To measure the effect of this occluded 'invisible' surface quantitatively, a bistable apparent motion display was used (Ramachandran and Anstis 1983a): two small rectangular-shaped targets changed their positions back and forth between two frames, and the disparity of a large centrally positioned rectangle was varied. When the perceived depths supported the possibility of amodal completion behind the large rectangle, increased vertical motion of the targets was found, suggesting that the amodal presence of the targets behind the occluder had effectively changed the center position of the moving targets for purposes of motion correspondence. Amodal contours are literally 'invisible', yet it is hypothesized that they have a neural representation at sufficiently early stages of visual processing to alter the correspondence solving process for apparent motion.

Attention↗
PubMed1990

Transparency: relation to depth, subjective contours, luminance, and neon color spreading.

The perception of transparency is highly dependent on luminance and perceived depth. An image region is seen as transparent if it is of intermediate luminance relative to adjacent image regions, and if it is perceived in front of another region and has a boundary which provides information that an object is visible through this region. Yet, transparency is not just the passive end-product of these required conditions. If perceived transparency is triggered, a number of seemingly more elemental perceptual primitives such as color, contour, and depth can be radically altered. Thus, with the perception of transparency, neon color spreading becomes apparent, depth changes, stereoscopic depth capture can be eliminated, and otherwise robust subjective contours can be abolished. In addition, we show that transparency is not coupled strongly to real-world chromatic constraints since combinations of luminance and color which would be unlikely to arise in real-world scenes still give rise to the perception of transparency. Rather than seeing transparency as a perceptual end-point, determined by seemingly more primitive processes, we interpret perceived transparency as much a 'cause', as an 'effect'. We speculate that the anatomical substrate for such mutual interaction may lie in cortical feed-forward connections which maintain modular segregation and cortical feedback connections which do not.

Attention↗
PubMed1989

Intuitive reasoning about probability: theoretical and experimental analyses of the "problem of three prisoners".

Among various Bayesian problems of probability, the "problem of three prisoners" (Lindley, 1971; Mosteller, 1965) is an especially good example which illustrates the drastic discrepancy between intuitive reasoning and mathematical formal reasoning about probability. In particular, it raises intriguing questions concerning the mathematical and cognitive relevance of factors such as prior probabilities and the context in which certain information is given. In the current paper, we report a new version of the problem which turned out to be even more counterintuitive. This new version was also designed so that different inferential schemes would lead to separate estimates of posterior probability. The data obtained from questionnaires and theoretical analyses of the original and modified problems suggest that: (1) The psychological processes of intuitive reasoning are qualitatively different from mathematical reasoning. (2) The tendency to neglect prior probabilities (Tversky & Kahneman, 1974, 1982) is not always the critical factor for illusory judgments. (3) Intuitive judgments can be categorized by several, distinctive propositional beliefs from which the judgments are apparently derived. We call these prototypical, crude beliefs "subjective theorems," and discuss their nature and roles in the current paper.

Adult↗
PubMed1989

Occlusion and the solution to the aperture problem for motion.

The "aperture problem" indicates that a local reading of the velocity of an oriented contour is inherently ambiguous, insufficient by itself to recover the velocity of image points. In Wallach's "barber pole" display consisting of moving diagonal lines within an elongated rectangular aperture, it has been suggested that the unambiguous motion of edge-terminators along the longer edges of the aperture propagates towards the motion-ambiguous center part of drifting stripes. This results in the perception of a surface moving in the direction of the longer axis of the aperture. By manipulating the stereoscopic disparity of a striped pattern relative to the aperture plane, we found that the disambiguating effects of terminators could be abolished if the striped pattern was in uncrossed disparity relative to the aperture plane. Also, the motion in 3 separate horizontally oriented, and vertically aligned apertures which would otherwise be seen as moving horizontally, was seen as "linked" together and moving vertically. This occurred only when the horizontally oriented segments separating these apertures were stereoscopically coded so that they appeared as occluders in front. These findings suggest that accidental or "extrinsic" terminators created by occluding edges are treated differently from real or "intrinsic" terminators, and that the real-world constraint of occlusion is thus implemented in the ambiguity-solving processes for motion.

Depth Perception↗
PubMed1989

Subjective contours, tilt aftereffects, and visual cortical organization.

The tilt aftereffect (TAE) was used to study interactions between real and subjective contours. Subjects adapted to either real or illusory lines and were then shown test stimuli containing real or illusory lines. In our first experiment, we found that there is a marked asymmetry in the interactions between real and subjective stimuli. Adaptation to real lines produces comparable TAEs with real and subjective test lines. With either type of test stimulus the maximum effect occurs with a 10-20 deg difference between the orientations of the adaptation and test stimuli. Also, there is a strong TAE when the adaptation and test stimuli contain only subjective lines. However, there is a significantly weaker TAE when the adaptation stimulus is subjective and the test stimulus is real. In a second experiment we find that interocular transfer of tilt aftereffects is greater when the test stimulus is subjective than when it is real. These results are consistent with physiological reports that a subset of orientation selective cells in visual cortex is responsive to subjective contours and that these cells are more binocular, on average, than those responsive only to real contours. Our findings also suggest that the perception of subjective contours is based on the activation of neurons with properties, such as orientation selectivity, which are characteristic of early visual cortical areas.

Adaptation, Ocular↗
PubMed1989

Stereoscopic depth: its relation to image segmentation, grouping, and the recognition of occluded objects.

Image regions corresponding to partially hidden objects are enclosed by two types of bounding contour: those inherent to the object itself (intrinsic) and those defined by occlusion (extrinsic). Intrinsic contours provide useful information regarding object shape, whereas extrinsic contours vary arbitrarily depending on accidental spatial relationships in scenes. Because extrinsic contours can only degrade the process of surface description and object recognition, it is argued that they must be removed prior to a stage of template matching. This implies that the two types of contour must be distinguished relatively early in visual processing and we hypothesize that the encoding of depth is critical for this task. The common border is attached to and regarded as intrinsic to the closer region, and detached from and regarded as extrinsic to the farther region. We also suggest that intrinsic borders aid in the segmentation of image regions and thus prevent grouping, whereas extrinsic borders provide a linkage to other extrinsic borders and facilitate grouping. Support for these views is found in a series of demonstrations, and also in an experiment where the expected superiority of recognition was found when partially sampled faces were seen in a back rather than a front stereoscopic depth plane.

Attention↗
PubMed1989

Mirror reversal by blind subjects in cutaneous perception and motor production of letters and numbers.

A letter drawn on the forehead is often perceived as its mirror reversal. Similarly, people produce mirror reversals when asked to write a letter on the underside of a table at which they are sitting. We varied the orientation and position of the stimulated or inscribed surface, and found several examples of these two mirror-reversal phenomena in blind subjects (who had no, or very little, visual experience), as well as in sighted subjects. Furthermore, the mirror-reversal rate of the two groups of subjects as a function of orientation and position of the surface was highly correlated. Thus, the mirror-reversal phenomena should be attributed to a nonvisual, spatial cognitive scheme that is perhaps shared by sighted and blind subjects.

Adult↗
PubMed1988

An occlusion-related mechanism of depth perception based on motion and interocular sequence.

Objects occlude other objects in natural scenes, and this occlusive relationship increases the spatio-temporal complexity of sensory inputs to the two eyes, especially when objects are moving. We ask whether the visual system can employ clever strategies which make use of real-world constraints on inputs to the eyes to determine the depth of objects. Employing psychophysical methods, we found that occlusion-related geometric rules, which constrain the relationship between the direction of motion and the order and asynchrony of eyes, are implemented at early stages of cortical visual processing.

Depth Perception↗