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 451 records · Page 25Linked to original sources
PubMed2000

Contour integration in color vision: a common process for the blue-yellow, red-green and luminance mechanisms?

We compare the performance of the red-green, blue-yellow and luminance postreceptoral mechanisms on a contour integration task requiring the linking of oriented Gabor elements across space to extract a winding 'path' or contour. We first establish that for all three mechanisms curvature and contrast are independent; losses in performance due to one cannot be compensated by changes in the other. We then compare contour integration by the three mechanisms using a method that controls for their differences in cone contrast thresholds. Our results show that despite the poor orientation discrimination thresholds and poor spatial sampling found for the blue-yellow mechanism, all three mechanisms perform similarly on contour integration over a wide range of curvatures. Furthermore, all three mechanisms have the same dependence on path curvature. We also investigate the effects of adding external orientation noise. Our results imply that the internal orientation noise for extracting 'aligned' path elements is similar in the three mechanisms and for all path curvatures, and the relative efficiencies are also similar for the three mechanisms. To account for our results, we propose that the three postreceptoral mechanisms use a common contour integration process. This linking process, however, cannot be color-blind; our last experiment shows that linking between different chromatic mechanisms or between opposite spatial phases disrupts contour integration. We thus propose that the common integration process remains sensitive to the color contrast and phase of its inputs.

Color Perception↗
PubMed2003

Object temporal connotation.

Recent studies show that what connotes an object is first of all a certain spatio-temporal structure. In this paper we describe some of the temporal features characterizing the temporal structure of objects: pre-existence, persistence, conservation of identity in spite of perceptive discontinuity, surviving changes in colour, size, and shape. We argue that time is an indispensable attribute for every type of object and briefly discuss the implication of this view with respect to a specific neuropsychological syndrome: unilateral spatial neglect.

Adult↗
PubMed2000

Neon colour spreading in three-dimensional illusory objects in humans.

We studied whether neon spreading can be induced within three-dimensional illusory triangles. Kanizsa triangles were induced by black pacman disks consisting of red sectors with curved sides. Viewing our stimuli monocularly produced two-dimensional illusory contours and surfaces as well as neon spreading in each figure. Triangles appeared concave or convex under stereoscopical viewing. Neon colour spreading was induced within illusory figures bending in three-dimensional space, suggesting that neural contour completion and surface filling-in interact across depth. Surprisingly, neon spreading was induced above the intervening surface even when the inducers were below the surface. Neon colour and illusory configuration were preserved behind the intervening surface only when it appeared transparent.

Adolescent↗
PubMed2001

Neural response to perception of volume in the lateral occipital complex.

Projection of a 3D scene onto the 2D retina necessarily entails a loss of information, yet perceivers experience a world populated with volumetric objects. Using simultaneous behavioral and neural (fMRI) measures, we identify neural bases of volume perception. Neural activity in the lateral occipital cortex increased with presentation of 3D volumes relative to presentation of 2D shapes. Neural activity also modulated with perceived volume, independent of image information. When behavioral responses indicated that observers saw ambiguous images as 3D volumes, neural response increased; when behavioral data revealed a 2D interpretation, neural response waned. Crucially, the physical stimulus was identical under both interpretations; only the percept of volume can account for the increased neural activity.

Adult↗
PubMed2003

At least at the level of inferior temporal cortex, the stereo correspondence problem is solved.

Stereoscopic vision requires the correspondence problem to be solved, i.e., discarding "false" matches between images of the two eyes, while keeping correct ones. To advance our understanding of the underlying neuronal mechanisms, we compared single neuron responses to correlated and anticorrelated random dot stereograms (RDSs). Inferior temporal neurons, which respond selectively to disparity-defined three-dimensional shapes, showed robust selectivity for correlated RDSs portraying concave or convex surfaces, but unlike neurons in areas V1, MT/V5, and MST, were not selective for anticorrelated RDSs. These results show that the correspondence problem is solved at least in far extrastriate cortex, as it is in the monkey's perception.

Animals↗
PubMed2003

Visual object processing in schizophrenia: evidence for an associative agnosic deficit.

Early studies suggested visual form perception impairment in schizophrenia. To re-examine this claim and characterise the deficit neuropsychologically, 41 schizophrenic patients were administered tests sensitive to different levels of visual object perception and recognition. Intellectually well-preserved patients were examined separately on these and additional tests. Single case analysis was also applied to four patients showing varying degrees of general intellectual impairment. As a group, the patients showed little impairment on tests of early visual object perception, but greater impairment on higher-level visual processing tests, in particular object recognition and naming. This held true for patients with preserved general intellectual function. Single case analysis suggested that patients with schizophrenia have a selective deficit affecting object recognition and identification, with a pattern similar to visual associative agnosia in neurological patients.

Adolescent↗
PubMed2003

The recognition of facial affect in autistic and schizophrenic subjects and their first-degree relatives.

BACKGROUND: Autism and schizophrenia are considered to be substantially influenced by genetic factors. The endophenotype of both disorders probably also includes deficits in affect perception. The objective of this study was to examine the capacity to detect facially expressed emotion in autistic and schizophrenic subjects, their parents and siblings. METHOD: Thirty-five subjects with autism and 102 of their relatives, 21 schizophrenic subjects and 46 relatives from simplex (one child affected) and multiplex (more than one child affected) families, as well as an unaffected control sample consisting of 22 probands completed a 50-item computer-based test to assess the ability to recognize basic emotions. RESULTS: The autistic subjects showed a poorer performance on the facial recognition test than did the schizophrenic and the unaffected individuals. In addition, there was a tendency for subjects from multiplex families with autistic loading to score lower on the test than individuals from simplex families with autistic loading. Schizophrenic subjects and their relatives as well as siblings and parents of autistic subjects did not differ from the sample of unaffected subjects in their ability to judge facial affect. CONCLUSIONS: Findings corroborate the assumption that emotion detection deficits are part of the endophenotype of autism. In families with autistic children, the extent of facial recognition deficits probably indexes an elevation in familial burden. It seems unlikely that problems in emotion perception form a consistent part of the endophenotype of schizophrenia or the broader phenotype in relatives of patients with psychosis or autism.

Adolescent↗
PubMedDate not supplied

Cortical projections to anterior inferior temporal cortex in infant macaque monkeys.

Inferior temporal (IT) cortex is a "high-order" region of extrastriate visual cortex important for visual form perception and recognition in adult primates. The pattern of cortical afferents from both ipsilateral and contralateral hemispheres to anterior IT cortex was determined in infant macaque monkeys 7-18 weeks of age following injections of wheat-germ agglutinin-HRP. Within the ipsilateral hemisphere, the locations and laminar distribution of labeled cells were similar to those observed after comparable injections in adult monkeys. Specifically, ipsilateral afferents derived from visual areas V4, TEO, anterior and posterior IT, and STP, from parahippocampal, perirhinal, and parietal zones, and from several anterior zones including lateral and ventral frontal cortex, the insula, and cingulate cortex. Within the contralateral hemisphere, we observed labeled cells in homotopic regions of IT and in parahippocampal and perirhinal areas, as has been reported for adult monkeys. However, we also identified additional contralateral regions not previously known to provide input to anterior IT, including lateral and ventral frontal cortex, cingulate cortex, and STP. Overall, the strongest and most widespread projections from outside the temporal lobe were found in the youngest monkey, suggesting that some of these projections may represent transient circuitry necessary for the development of complex visual response properties in anterior IT.

Afferent Pathways↗
PubMedDate not supplied

Simulation of neuronal responses defining depth order and contrast polarity at illusory contours in monkey area V2.

Neurophysiological, brain imaging, and perceptual studies in animals and humans suggest that illusory (occluding) contours are represented at an early level of visual cortical processing. Comparatively little is known about the mechanisms defining the depth order and the brightness illusion associated with such contours. Baumann et al. (1997) found neurons in area V2 of the alert monkey that signaled not only illusory contours but also the figure-ground direction that human observers perceive at such contours. The majority of these neurons showed this property independent stimulus contrast; a small minority preferred a certain combination of figure-ground direction and contrast polarity at these contours. In this article, we simulate the responses of these neurons by means of a grouping mechanism that uses occlusion cues (line-ends, corners) to define figure-ground direction and contrast polarity at such contours.

Animals↗
PubMed1998

Continuity in tactual-visual cross-modal transfer: infancy to 11 years.

The present study demonstrated that individual differences in cross-modal transfer showed continuity over a 10-year span. Tactual-visual tasks, requiring visual recognition of shapes that had previously been felt but not seen, were given to full-term and preterm children at 2 ages, 1 and 11 years. Cross-modal performance showed a left-hand advantage at 11 years and, for both groups, cross-age correlations were significant when tactual exploration at 11 years was done with the left hand (r = .34-.36). The continuity showed some specificity in that the infant measure did not relate to other types of cross-modal performance at 11 years and was not dependent on aspects of spatial ability involving form perception. This continuity accounted for most of the previously reported relation of infant cross-modal ability to 11-year IQ.

Child↗
PubMed1984

Measuring efficiency of selection from briefly exposed visual displays: a model for partial report.

In the proposed model for partial report, performance reflects the number of targets in a short-term memory buffer. The total number of items (targets, distractors, or extraneous noise) entering the buffer is independent of the number of targets and distractors in the stimulus. Entrance is determined by selective sampling according to a Luce (1959) ratio rule. The model was tested in a variety of conditions with partial reports based on brightness, color, shape, or alphanumeric class. With three parameters, the model accounted for 99% of the variance with number of targets and number of distractors in data obtained by averaging across conditions. Parameter K (number of items entering the buffer) showed little variation with the selection criterion, and estimates for parameter epsilon (total impact of extraneous noise with impact per target as the unit) were rather small. Estimates for parameter alpha (impact per distractor with impact per target as the unit) varied widely across conditions. Parameter alpha is a measure for the efficiency of selecting targets rather than distractors.

Adult↗
PubMed1987

Spatial layout, orientation relative to the observer, and perceived projection in pictures viewed at an angle.

Judgments of the spatial layout of a three-dimensional array of pictured dowels remain relatively constant as viewing angle changes, whereas judgments of their orientation relative to the observer (perceived orientation) vary. These changes in perceived orientation as viewing angle changes, called the differential rotation effect (DRE), also occur for stimuli such as the eyes in portraits, which are not extended in pictorial space. Thus, the mechanism for the DRE does not depend on the extension of pictured objects in depth. The DRE is decreased when back-illuminated pictures are viewed in the dark so that the picture plane is not visible. This result suggests that the DRE depends on information that defines a pictured object's direction relative to the picture plane. The difference in the way spatial layout and perceived orientation are affected by changes in viewing angle suggests that it is important to distinguish between these two attributes of pictures. In addition, another attribute, the picture's projection, should be distinguished from spatial layout and perceived orientation. When these distinctions are not made, the result is confusion, particularly when discussing whether or not pictures viewed at an angle appear distorted.

Attention↗
PubMed1988

The distorted room illusion, equivalent configurations, and the specificity of static optic arrays.

The distorted room illusion (DRI) and the attendant argument for perceptual ambiguity is critically analyzed from a Gibsonian/ecological point of view. The notions of multiple specification, conflicting information, and perceptual skill are invoked in showing how the ecological approach can accommodate illusion effects that may remain under mobile binocular viewing conditions. Static optic arrays are shown not to be ambiguous. So-called equivalent configurations are found to be analytic artifacts, appearing when the problem of information is treated in geometrical terms without regard for constraints due to physical and ecological regularities. The relative importance of motion-based and motion-independent information is discussed.

Depth Perception↗
PubMed1988

Affine distortions of pictorial space: some predictions for Goldstein (1987) that La Gournerie (1859) might have made.

Goldstein (1987) studied the perception of pictures seen from the front and the side. Several distinctions arose from his results and analysis, but only one is central to the reanalysis presented here: The perceived orientation of objects within a picture with respect to the external world is a function of viewer position in front of the picture. For example, the eyes of a portrait subject appear to follow an observer who moves around a gallery. Viewed from many positions, such objects can be said to rotate, following a mobile viewer. Goldstein called this the differential rotation effect because those objects that point directly out of the picture (at 90 degrees) rotate most; those pointing at other angles rotate in decreasing amounts. Goldstein offered no theoretical model and little in the way of explanation for this effect. This Observation offers a model based on the affine geometry and the analyses of La Gournerie (1859). This analysis transforms pictorial space (the space behind a photograph or representational picture) by shears, compressions, and dilations according to the viewpoint of the observer in relation to the composition point of the picture. These effects account for Goldstein's differential rotation effect quite well.

Depth Perception↗
PubMed1988

Geometry or not geometry? Perceived orientation and spatial layout in pictures viewed at an angle.

Cutting (1988) suggests that changes in the perceived orientations of pictured objects that occur with changes in viewing angle are caused by the geometrical changes that accompany these changes in viewing angle. His geometrical analysis does predict the differential rotation effect reported by Goldstein (1979, 1987), but fails to predict other important aspects of the data. Cutting's analysis does, however, support Goldstein's (1987) conclusion that in future research on picture perception it is important to clearly distinguish between the attributes of perceived orientation and spatial layout.

Depth Perception↗
PubMed1988

Sequence influence on the organization of meaningless serial stimuli: economy after all.

This article provides evidence for an extension of structural information theory, a theory which describes perceptual organization formally, into a more general theory of representation that takes the role of organizations obtained earlier into account. In eight experiments, subjects study series of colored dots. Each series contained 6-8 dots of different colors, and viewing time was between 400 ms and 60 s. In several experimental procedures, subjects recalled the series presented. The experiments systematically varied the economy of the organizations of the series as described by structural information theory as well as a number of aspects of the context in which the series were presented, like order of presentation of a series, order between the series, viewing span, viewing time, and recall procedure. Recall was influenced both by the economy as well as by the context. It is shown how the context influences the relative strength of the most economical organization as compared with rival, local organizations. A structured network model is presented that accounts for the influence of both the economy and the context.

Adult↗