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Results for “Depth Perception”

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PubMed1980

Event perception.

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Blindness↗
PubMed2001

Cortical mechanisms of binocular stereoscopic vision.

The early neurophysiology of binocular vision is largely dominated by measurements of disparity selectivity in cortical neurons in various visual areas. Incisive progress has been made by the intensive study of the mechanism of disparity selectivity of V1 in cortical neurons and the development of a number of tests for the involvement of single neurons in the perception of stereoscopic depth. The picture that now emerges is that cortical area V1 must be a preliminary processing stage for the analysis of stereoscopic depth, whereas some of the extrastriate areas may actually be responsible for the generation of neuronal signals that underlie the perception of binocular depth.

Animals↗
PubMed2002

Disparity capture by flanking stimuli: a measure for the cooperative mechanism of stereopsis.

In this work the range and scaling properties of the cooperative (contextual) interaction that was first proposed by Julesz [Foundations of Cyclopean Perception, University of Chicago Press, Chicago, 1971] to address the correspondence problem in stereopsis is measured. To this end the effect that flanking difference of Gaussians (DoG) patches produce on a perception of a target pair of patches is studied. The relative depth configuration of the target pair can switch from the small disparity gradient to a large disparity gradient state as a result of cooperative effects of the flanking stimuli. It is found that the interaction strength falls with distance. Its range varies for different subjects from 2 to 3 DoG patch sizes and scales proportionally to the size of the stimuli. The results suggest that a very localized cooperative interaction is in effect at a broad range of spatial scales.

Algorithms↗
PubMed1991

Midwife/client relationship: midwives' perspectives.

This study set out to explore midwives' understanding of the factors which affected the development of a therapeutic relationship with clients. A qualitative approach was adopted for the study to avoid placing predetermined categories upon midwives' perceptions. Because of the qualitative nature of the study in-depth interviews were conducted to allow midwives to explore in depth their perceptions of the research topic. Themes identified within the interview data indicated conflicting needs/interests which in turn seemed to cause dilemmas for the midwives interviewed. It seemed appropriate therefore to take the data analysis one step further by utilising dilemma analysis. Consideration of the situations in which the midwives experienced 'good' or 'poor' relationships revealed a complex picture of the factors affecting relationships with clients. Four main issues were identified: the nature and value of the midwives' role; recognition of authority/autonomy in practising this role; emotional involvement with clients; and maintaining personal integrity. From dilemma analysis of the data it appears that when midwives were successful in managing these issues then the relationship became 'special' and therapeutic for clients. Mismanagement of these issues in contrast led to dilemmas which then inhibited development of meaningful relationships between the midwives and clients. In view of the fact that clients and midwives value this 'special' relationship a case is made for midwives to be prepared educationally to manage effectively issues which are raised in their everyday practice. Only then will the midwife/client relationship become therapeutic.

Clinical Nursing Research↗
PubMed1988

Integration of depth modules: stereo and shading.

We studied the integration of image disparities, edge information, and shading in the three-dimensional perception of complex yet well-controlled images generated with a computer-graphics system. The images showed end-on views of flat- and smooth-shaded ellipsoids, i.e., images with and without intensity discontinuities (edges). A map of perceived depth was measured by adjusting a small stereo depth probe interactively to the perceived surface. Our data show that disparate shading (even in the absence of disparate edges) yields a vivid stereoscopic depth perception. The perceived depth is significantly reduced if the disparities are completely removed (shape-from-shading). If edge information is available, it overrides both shape-from-shading and disparate shading. Degradations of depth perception corresponded to a reduced depth rather than to an increased scatter in the depth measurement. The results are compared with computer-vision algorithms for both single cues and their integration for three-dimensional vision.

Computer Graphics↗
PubMed2005

A new look at binocular stereopsis.

We report a new phenomenon, which illustrates that the role of binocular disparity in 3D shape perception critically depends on whether the parts are interpreted as belonging to a single object. The nature of this phenomenon was studied in four experiments. In the first two experiments the subjects were shown a sequence of stereoscopic images of a cube, in which binocular disparity indicated that the individual parts move towards or away from one eye. However, when the parts of the cube were perceived as elements of a single object, they appeared to move in a rigid fashion and the direction of motion was orthogonal to that predicted by the binocular disparities. The third experiment generalized these results to more complex polyhedra. The last experiment showed that constraints related to motion, such as rigidity, are important, but not critical for this phenomenon to occur. All these results imply that the interpretation as to what corresponds to a single object affects the importance (weight) of binocular disparity and may even eliminate its contribution altogether; the percept of a 3D shape is dominated by a priori constraints, and depth cues play a secondary role.

Cues↗
PubMed2000

A slowly moving foreground can capture an observer's self-motion--a report of a new motion illusion: inverted vection.

We investigated interactions between foreground and background stimuli during visually induced perception of self-motion (vection) by using a stimulus composed of orthogonally moving random-dot patterns. The results indicated that, when the foreground moves with a slower speed, a self-motion sensation with a component in the same direction as the foreground is induced. We named this novel component of self-motion perception 'inverted vection'. The robustness of inverted vection was confirmed using various measures of self-motion sensation and under different stimulus conditions. The mechanism underlying inverted vection is discussed with regard to potentially relevant factors, such as relative motion between the foreground and background, and the interaction between the mis-registration of eye-movement information and self-motion perception.

Adult↗
PubMed2000

The generic-viewpoint assumption and illusory contours.

Visual images are ambiguous. Any image, or collection of images, is consistent with an infinite number of possible scenes in the world. Yet we are generally unaware of this ambiguity. During ordinary perception we are generally aware of only one, or perhaps a few of these possibilities. Human vision evidently exploits certain constraints--assumptions about the world and images formed of it--in order to generate its perceptions. One constraint that has been widely studied by researchers in human and machine vision is the generic-viewpoint assumption. We show that this assumption can help to explain the widely discussed fact that outlines of blobs are ineffective inducers of illusory contours. We also present a number of novel effects and report an experiment suggesting that the generic-viewpoint assumption strongly influences illusory-contour perception.

Adult↗
PubMed1990

Use of subjective information in scientific psychology: III. The internal image during visual perception: an introspectionist analysis.

On the basis of personal observation, the writer describes certain characteristics of hypnopompic visual imagery that lead to an understanding of how the internal visual image is experienced. This understanding helps us to see how an internal two-dimensional visual perceptual image could be experienced as an external environment positioned around the observer. The writer suggests how the three-dimensionalized perceptual image is constructed, how it gives the effect of directional looking within the context of seeing widely, and how certain features of visual perception can best be accounted for by the mediation of perception by an internal image.

Attention↗
PubMed1995

3-D shape perception.

In this paper, we analyze and test three theories of 3-D shape perception: (1) Helmholtizian theory, which assumes that perception of the shape of an object involves reconstructing Euclidean structure of the object (up to size scaling) from the object's retinal image after taking into account the object's orientation relative to the observer, (2) Gibsonian theory, which assumes that shape perception involves invariants (projective or affine) computed directly from the object's retinal image, and (3) perspective invariants theory, which assumes that shape perception involves a new kind of invariants of perspective transformation. Predictions of these three theories were tested in four experiments. In the first experiment, we showed that reliable discrimination between a perspective and nonperspective image of a random polygon is possible even when information only about the contour of the image is present. In the second experiment, we showed that discrimination performance did not benefit from the presence of a textured surface, providing information about the 3-D orientation of the polygon, and that the subjects could not reliably discriminate between the 3-D orientation of textured surface and that of a shape. In the third experiment, we compared discrimination for solid shapes that either had flat contours (cuboids) or did not have visible flat contours (cylinders). The discrimination was very reliable in the case of cuboids but not in the case of cylinders. In the fourth experiment, we tested the effectiveness of planar motion in perception of distances and showed that the discrimination threshold was large and similar to thresholds when other cues to 3-D orientation were used. All these results support perspective invariants as a model of 3-D shape perception.

Attention↗
PubMed1998

Types of shear disparity and the perception of surface inclination.

A study is reported of (i) the perceived inclination of a textured surface in depth about a horizontal axis as a function of disparity magnitude for horizontal-shear disparity, vertical-shear disparity, and rotation disparity; and (ii) interactions between patterns with shear or rotation disparity and superimposed or adjacent patterns or lines with zero disparity. Horizontal-shear disparity produced strong inclination which was enhanced by superimposed or adjacent zero-disparity stimuli. It produced little or no inclination contrast in superimposed or adjacent zero-disparity stimuli. Vertical-shear disparity produced inclination in the opposite direction (induced effect) which was reduced to near zero by a superimposed zero-disparity pattern. Adjacent vertical-shear and zero-disparity patterns appeared inclined at slightly different angles with a wide curved boundary. This suggests that vertical-shear disparities are averaged over a wide area. Rotation disparity produced minimal inclination. A superimposed or adjacent zero-disparity line appeared strongly inclined. A superimposed or adjacent zero-disparity pattern appeared vertical and caused the pattern with rotation disparity to appear inclined. Four mechanisms are proposed to account for the results: depth contrast, depth enhancement, deformation-disparity processing, and disparity transfer arising from cyclovergence.

Computers↗
PubMed2006

Bayesian models of binocular 3-D motion perception.

Psychophysical studies on three-dimensional (3-D) motion perception have shown that perceived trajectory angles of a small target traveling in depth are systematically biased. Here, predictions from Bayesian models, which extend existing models of motion-first and stereo-first processing, are investigated. These statistical models are based on stochastic representations of monocular velocity and binocular disparity input in a binocular viewing geometry. The assumption of noise in these inputs together with a plausible prior for 3-D motion leads to testable predictions of perceived trajectory angle and velocity. Results from two experiments are reported, suggesting that disparity rather than motion processing introduces perceptual bias.

Bayes Theorem↗