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Results for “VISUAL PERCEPTION”

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At least 37 records · Page 2Linked to original sources
PubMed2005

Dissociation between visual perception of allocentric distance and visually directed walking of its extent.

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.

Adult↗
PubMed1994

The generic viewpoint assumption in a framework for visual perception.

A visual system makes assumptions in order to interpret visual data. The assumption of 'generic view' states that the observer is not in a special position relative to the scene. Researchers commonly use a binary decision of generic or accidental view to disqualify scene interpretations that assume accidental viewpoints. Here we show how to use the generic view assumption, and others like it, to quantify the likelihood of a view, adding a new term to the probability of a given image interpretation. The resulting framework better models the visual world and reduces the reliance on other prior assumptions. It may lead to computer vision algorithms of greater power and accuracy, or to better models of human vision. We show applications to the problems of inferring shape, surface reflectance properties, and motion from images.

Humans↗
PubMed1994

Intact visual imagery and impaired visual perception in a patient with visual agnosia.

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several reports in which they are dissociated. Evidence for the separability of these processes is provided by a patient, C.K., who has a profound visual object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. was able to draw objects in considerable detail from memory, and his knowledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and perception. Interestingly, C.K. could also recognize newly constructed objects in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.

Adult↗
PubMed1976

Physiological aspects of visual perception. I. Functional aspects of visual cortex.

The first part of the Bennett Lecture for 1975 is a description of the dissociation of visual perception in the macaque monkey by ablation of area 17 on the one hand, and of areas 18 and 19 on the other. Bilateral removal of area 17, with careful preservation of a great part of areas 18 and 19, and of the inferior pulvinar, resulted in loss of binocular fixation, loss of visual recognition of still objects, and loss of visuosocial behavior such as grimacing and vocalization. There remained excellent visuospatial orientation and reaching for moving peripheral visual targets. Removal of areas 18 and 19, with isolation of area 17 from the remainder of cortex, was accomplished in two animals and left intact the ability to distinguish and sort out still objects by vision, with intact fixation, and visuosocial behavior. Spatial orientation was then easily confused by movement.

Animals↗
PubMed1989

[Visual perception and its disorders].

It's the brain and not the eye that decides what is perceived. In spite of this fact, quite a lot is known about the functioning of the eye and the first sections of the optic tract, but little about the actual process of perception. Examination of visual perception and its malfunctions relies therefore on certain hypotheses. Proceeding from the model of functional brain systems, variant functional domains of visual perception can be distinguished. Among the more important of these domains are: digit span, visual discrimination and figure-ground discrimination. Evaluation of these functional domains allows us to understand those children with disorders of visual perception better and to develop more effective treatment methods.

Brain↗
PubMedDate not supplied

Fundamentally misunderstanding visual perception. Adults' belief in visual emissions.

The authors reviewed research about a profound misconception that is present among college students, namely, the belief that the process of vision includes emanations from the eyes, an idea that is consistent with the extramission theory of perception, which was originally professed by early Greek philosophers and which persisted in scholarly circles for centuries. The authors document the strength and breadth of this phenomenon and the object failure of traditional educational techniques to overcome this belief, and they reveal that students are leaving psychology courses with a flawed understanding of one of the most studied processes in the history of psychology--visual perception. Some suggestions are offered for overcoming this misconception in traditional college classroom settings.

Adolescent↗
PubMedDate not supplied

Interpolation processes in the visual perception of objects.

Visual perception of objects depends on segmentation and grouping processes that act on fragmentary input. This paper gives a brief overview of these processes. A simple geometry accounting for contour interpolation is described, and its applications to 2D, 3D, and spatiotemporal object interpolation processes are considered. A method is described for distinguishing interpolation based on this geometry from more global or top-down influences. Results suggest a separation between interpolation based on relatively local stimulus relations, which give rise to precise boundary representations, and processes involving recognition from partial information, which do not. Aspects of the model-especially the unified treatment of illusory and occluded objects-raise questions about the nature of seeing. Although it is often believed that illusory objects are perceived, while occluded objects are inferred, I suggest that both research and theory converge in supporting a more unified account. Illusory and occluded contours and surfaces do not divide into the real, the perceived, and the inferred, but are all represented, and in key respects, derive from identical perceptual processes.

Neural Networks, Computer↗
PubMed2002

Revision: is visual perception a requisite for visual imagery?

Vision is the most highly developed sense in man and represents the doorway through which most of our knowledge of the external world arises. Visual imagery can be defined as the representation of perceptual information in the absence of visual input. Visual imagery has been shown to complement vision in this acquisition of knowledge--it is used in memory retrieval, problem solving, and the recognition of properties of objects. The processes underlying visual imagery have been assimilated to those of the visual system and are believed to share a neural substrate. However, results from studies in congenitally and cortically blind subjects have opposed this hypothesis. Here I review the currently available evidence.

Blindness↗
PubMed1990

Fresnel prisms improve visual perception in stroke patients with homonymous hemianopia or unilateral visual neglect.

We randomly assigned 39 patients with stroke and homonymous hemianopia or unilateral visual neglect to treatment with 15-diopter plastic press-on Fresnel prisms (n = 18) or to serve as controls (n = 21). Baseline evaluations of visual perception and activities-of-daily-living (ADL) function were similar for both groups. After 4 weeks, the prism-treated group performed significantly better than controls on the following: (1) Motor Free Visual Perception Test; (2) Line Bisection Task; (3) Line Cancellation Task; (4) Harrington Flocks Visual Field Screener; and (5) Tangent Screen Examination. There was no significant difference in Barthel ADL assessment at 4 weeks. Thus, treatment with 15-diopter Fresnel prisms improves visual perception test scores but not ADL function in stroke patients with homonymous hemianopia or unilateral visual neglect.

Aged↗
PubMed2004

Visual memory and visual perception recruit common neural substrates.

This human neuroimaging review aims to determine the degree to which visual memory evokes activity in neural regions that have been associated with visual perception. A visual perception framework is proposed to identify cortical regions associated with modality-specific processing (i.e., visual, auditory, motor, or olfactory), visual domain-specific processing (i.e., "what" versus "where," or face versus visual context), and visual feature-specific processing (i.e., color, motion, or spatial location). Independent assessments of visual item memory studies and visual working memory studies revealed activity in the appropriate cortical regions associated with each of the three levels of visual perception processing. These results provide compelling evidence that visual memory and visual perception are associated with common neural substrates. Furthermore, as with visual perception, they support the view that visual memory is a constructive process, in which features or components from disparate cortical regions bind together to form a coherent whole.

Cerebral Cortex↗