PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Form Perception”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93Linked to original sources
PubMed1983

The multiple determination of illusory contours: 2. An empirical investigation.

Judgments of contour strength or saliency for twenty-four illusory-contour configurations were subjected to a confirmatory factor analysis. A four-factor model that posited the involvement of simultaneous contrast, linear effects (assimilation and dissimilation), depth/completion cues, and feature analyzers accounted for a substantial proportion of the variance in judgments of illusory-contour strength. The hierarchical addition of a fifth factor, diffuse illusory contours, significantly improved the overall fit of the model, but added little to the proportion of explained variance. The taxonomic approach adopted provides support for a multiprocess model of illusory-contour perception.

Adolescent↗
PubMed1983

Evidence relating subjective contours and interpretations involving interposition.

Subjective contours, according to one theory, outline surfaces that are apparently interposed between the viewer and background (because of the disruption of background figures, sudden termination of lines, and other interposition 'cues') but are not explicitly outlined by intensity discontinuities. This theory predicts that if the cues are not interpreted as evidence of interposition, no intervening surface need be postulated, hence no subjective contours would be seen. This prediction, however, is difficult to test because observers normally interpret the cues as interposition evidence and normally see the subjective contours. Tests are reported on a patient with visual agnosia who is unable to make the usual interposition interpretations and unable to see subjective contours, but has normal ability to interpret standard visual illusions, stereograms, and in particular, stereogram versions of the standard subjective contour figures, which elicit to him strong subjective edges in depth (corresponding to the subjective contours viewed in the monocular versions of the figures.

Aged↗
PubMed1983

Visual apparent movement: transformations of size and orientation.

Sequential alternation between same-shaped stimuli differing in size (size ratio s) and orientation (angular difference v) produced a visual illusion of translation in depth and concurrent rotation. The minimum stimulus-onset asynchrony required for the appearance of a rigidly moving object was approximately a linearly increasing function of (s-1)/(s+1) for simple translation in depth and a linearly increasing function of v for simple rotation. The extrapolated zero intercept was lower for translation than for rotation, but estimated transformation times were additive in combined transformations. The results suggest that (a) the processes of apparent translation in depth and apparent rotation are individually sequential-additive in structure, and (b) apparent translations and rotations are combined by fine-grained alternation of steps of apparent translation and steps of apparent rotation. Similar principles account for recent data on imagined spatial transformations of visual size and orientation.

Depth Perception↗
PubMed1983

Triangles and squares look smaller than they are: some new illusions of extent.

Some new illusions of extent are described, and they are discussed in relation to the Müller-Lyer illusion and the constancy-scaling hypothesis. It is concluded that they support a minimal version of this hypothesis in which certain configurations of lines cause changes in local scale in certain directions, independently of whether or not these configurations are incorporated in larger patterns in a way which supports and receives a depth interpretation.

Depth Perception↗
PubMed1984

Information about three-dimensional shape and direction of illumination in a square-wave grating.

A homogeneous grey picture and a 'Mondrian' type of picture were illuminated by a projector with square-wave gratings of thirty different contrast values used as slides. Ten observers reported whether the picture appeared three-dimensional (3-D) (pleated) or flat. 3-D responses in this situation indicate colour constancy 'at the cost of' nonveridical depth perception. The frequencies of 3-D responses were significantly higher for the structured picture than for the homogeneous grey one. In reports of the direction from which the apparent 3-D object appeared to be illuminated there was a significant preference for responses "from above" when the grating was horizontally oriented. With vertical orientation there was no preference for "from the left" or "from the right". The results from the first experiment contradict traditional cue theories of depth perception since the projection of the borders between the fields of the structured picture was invariant and expected to inform about the flatness of the picture. They are, however, in line with a model for perceptual analysis of reflected light into common and relative components proposed earlier by Bergström. The difference in perceived direction of illumination between horizontally and vertically orientated gratings is discussed in connection with human ecology.

Color Perception↗
PubMed1987

Stereokinesis with moving visual phantoms.

When a flat pattern composed of a solid ellipse with two symmetrical semirings (corresponding to the visible parts of a contour ellipse whose major axis is perpendicular to that of the solid ellipse) is slowly rotated in the frontoparallel plane, a compelling three-dimensional impression occurs. Subjects report seeing an egg-shaped object that is inserted into a circular ring: the two objects move solidly into three-dimensional space and a moving visual phantom is generated so that the ring appears completed by an illusory curved bar in the region closest to the observer during rotation. A number of variations of this illusion are presented. It is shown that stereokinetic phantoms (i) maintain the shape of the inducing elements; (ii) appear only after the stereokinetic transformation has taken place; and (iii) depend on the organization of the three-dimensional percept as a whole. Relations between stereokinetic phantoms and other completion phenomena are presented and discussed.

Depth Perception↗
PubMed1987

The influence of auditory stimulation on a visual oblique effect.

It has previously been reported by Smets that there is an increase in the magnitude of the monocular oblique effect when a 70 dB(A), 1 kHz acoustic stimulus is presented contralaterally, but not ipsilaterally, to the viewing eye. This finding was interpreted as one which provided difficulties both for data-driven models of information processing and for the cortical simple cell explanation of the oblique effect. There are several logical and methodological difficulties in Smets's paper, and in the two experiments reported here the effect found by Smets was not replicated. The failure to observe the effect was robust under conditions that maximised the possibility of neural interaction. It is concluded that acoustic stimulation does not affect the magnitude of the oblique effect.

Attention↗
PubMed1987

Line correspondence in binocular vision.

The mathematical analysis of binocular vision introduced by Helmholtz is applied to the problem of the use of disparity information to position a stimulus in depth. It is shown that matching the images from the left and right eyes along radial directions is an alternative to matching images along the horizontal direction only.

Attention↗
PubMed1987

The way the ball bounces: visual and auditory perception of elasticity and control of the bounce pass.

Human observers may perceive not only spatial and temporal dimensions of the environment, but also dynamic physical properties that are useful for the control of behavior. A study is presented in which visual and auditory perception of elasticity in bouncing objects, which was specified by kinematic (spatiotemporal) patterns of object motion, were examined. In experiment 1, observers could perceive the elasticity of a bouncing ball and were able to regulate the impulse applied to the ball in a bounce pass. In experiments 2 and 3, it was demonstrated that visual perception of elasticity was based on relative height information, when it was available, and on the duration of a single period under other conditions. Observers did not make effective use of velocity information. In experiment 4, visual and auditory period information were compared and equivalent performance in both modalities was found. The results are interpreted as support for the view that dynamic properties of environmental events are perceived by means of kinematic information.

Adult↗
PubMed1987

Serial and parallel search in pattern vision?

The nature of the processing of combinations of stimulus dimensions in human vision has recently been investigated. A study is reported in which visual search for suprathreshold positional information--vernier offsets, stereoscopic disparity, lateral separation, and orientation--was examined. The initial results showed that reaction times for visual search for conjunctions of stereoscopic disparity and either vernier offsets or orientation were independent of the number of distracting stimuli displayed, suggesting that disparity was searched in parallel with vernier offsets or orientation. Conversely, reaction times for detection of conjunctions of vernier offsets and orientation, or lateral separation and each of the other positional judgements, were related linearly to the number of distractors, suggesting serial search. However, practice has a significant effect upon the results, indicative of a shift in the mode of search from serial to parallel for all conjunctions tested as well as for single features. This suggests a reinterpretation of these and perhaps other studies that use the Treisman visual search paradigm, in terms of perceptual segregation of the visual field by disparity, motion, color, and pattern features such as colinearity, orientation, lateral separation, or size.

Attention↗
PubMed1988

Dynamic occlusion and motion parallax in depth perception.

Random-dot techniques were used to examine the interactions between the depth cues of dynamic occlusion and motion parallax in the perception of three-dimensional (3-D) structures, in two different situations: (a) when an observer moved laterally with respect to a rigid 3-D structure, and (b) when surfaces at different distances moved with respect to a stationary observer. In condition (a), the extent of accretion/deletion (dynamic occlusion) and the amount of relative motion (motion parallax) were both linked to the motion of the observer. When the two cues specified opposite, and therefore contradictory, depth orders, the perceived order in depth of the simulated surfaces was dependent on the magnitude of the depth separation. For small depth separations, motion parallax determined the perceived order, whereas for large separations it was determined by dynamic occlusion. In condition (b), where the motion parallax cues for depth order were inherently ambiguous, depth order was determined principally by the unambiguous occlusion information.

Attention↗
PubMed1989

Depth interpolation with sparse disparity cues.

The interpolation of stereoscopic depth given only sparse disparity information was investigated. The basic stimulus was a rectangle with zero disparity at one edge, and 20 or 30 min visual angle disparity at the other. The depth assigned to the ambiguous intervening locations was measured by means of a small briefly-flashed binocular comparison spot. For a stimulus consisting of a uniform rectangle presented on a background of random dots with zero disparity, interpolated depth was greater for a high mean contrast between rectangle and background than for a low mean contrast. Relative to a linear interpolation between the edges, a larger difference in edge disparity resulted in poorer depth interpolation. Depth interpolation based on rivalrous information was examined by filling the stimulus rectangle with narrow-band filtered noise which was uncorrelated between the two eyes. Four different passbands which were matched in apparent contrast were investigated. The results demonstrate that the rivalrous low-spatial-frequency content was resistant to interpolation; rivalrous high spatial frequencies did not interfere with depth interpolation. High-spatial-frequency stimuli yielded a percept similar to the uniform-field condition, whereas low-spatial-frequency stimuli lay in a depth plane near or even behind the background. In the latter case a transparent plane was perceived which was linearly interpolated between the two edges, and which floated above the rivalrous noise.

Attention↗
PubMed1990

Illusory contours from pictorially three-dimensional inducing elements.

Illusory-figure patterns which are composed of pictorial elements representing three-dimensional partial disks are sometimes effective and sometimes not. When they are not effective, it is apparently because they contain information that contradicts the presence of an occluding figure and/or because all of the edges within the pattern are seen as edges of various pictured surfaces of the elements.

Attention↗
PubMed1992

Recognising faces: effects of lighting direction, inversion, and brightness reversal.

When information about three-dimensional shape obtained from shading and shadows is ambiguous, the visual system favours an interpretation of surface geometry which is consistent with illumination from above. If pictures of top-lit faces are rotated the resulting stimulus is both figurally inverted and illuminated from below. In this study the question of whether the effects of figural inversion and lighting orientation on face recognition are independent or interactive is addressed. Although there was a clear inversion effect for faces illuminated from the front and above, the inversion effect was found to be reduced or eliminated for faces illuminated from below. A strong inversion effect for photographic negatives was also found but in this case the effect was not dependent on the direction of illumination. These findings are interpreted as evidence to suggest that lighting faces from below disrupts the formation of surface-based representations of facial shape.

Adult↗
PubMed1992

Curvature is a basic feature for visual search tasks.

A curved target can be found efficiently among straight distractors in a visual search task. This could reflect the status of curvature as a basic feature for visual search. Alternatively, curvature could be detected as a locus of high variation in orientation. In a series of experiments it is shown that efficient search for curvature is possible even if local variation in orientation is eliminated as a cue. This suggests that curvature is part of the set of basic features for visual search and that this set is derived relatively late in the course of visual processing.

Adult↗