PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Visual 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 1,243 records · Page 69Linked to original sources
PubMedDate not supplied

[The specific features of the work of the visual mechanisms in the right and left hemispheres of the human brain].

Disturbances in the visual perception were analysed in groups of patients after commissurotomy, unilateral electroshock therapy, local brain lesions in the structure of the visual system. Three groups of symptoms were distinguished, i. e., deficit in attention switching, defects of image fragment recognition, and disturbances in assessment of special relations between the fragments and their groups. It was shown that these groups of symptoms were variously expressed in disorders of visual perception during pathologically autonomous activity of the left or right hemisphere. A model concept of hemispheric specificity in the visual perception is developed.

Brain↗
PubMed1991

Selective effects of low doses of apomorphine on spatiotemporal contrast sensitivity in healthy volunteers: a double-blind placebo-controlled study.

1. Apomorphine (1 and 5 micrograms kg-1) and placebo were given to nine normal volunteers, using a Latin-square design and double-blind procedures. The visual perception of static and moving patterns (static and motion contrast sensitivity) was evaluated before and 15 min after the dose administration. 2. Apomorphine (1 and 5 micrograms kg-1), as compared with placebo, led to a significant overall reduction of the visual perception of movement. This effect was dose-related, and apomorphine (5 micrograms kg-1) induced a more pronounced decrease in the visual perception of movement than apomorphine (1 microgram kg-1). With apomorphine (5 micrograms kg-1), the reduction was more pronounced for low spatial frequencies, and was linearly inversely correlated to the spatial frequency for a temporal frequency of 3 Hz. Finally, no significant effect of apomorphine was observed for sensitivity to static patterns. 3. Several non exclusive hypotheses may be suggested: The effects of apomorphine may result from stimulation of retinal D1- and/or D2-dopaminergic receptors. Apomorphine may increase the surround inhibition of ganglion cells' receptive-fields. This modification of the centre-surround balance may explain the decrease in contrast sensitivity for low spatial frequencies. The specific effects of apomorphine on the visual perception of movement support the hypothesis that apomorphine preferentially affects the magnocellular pathway which mediates sensitivity to moving patterns.

Adult↗
PubMed2003

Perceptual organization of local elements into global shapes in the human visual cortex.

The question of how local image features on the retina are integrated into perceived global shapes is central to our understanding of human visual perception. Psychophysical investigations have suggested that the emergence of a coherent visual percept, or a "good-Gestalt", is mediated by the perceptual organization of local features based on their similarity. However, the neural mechanisms that mediate unified shape perception in the human brain remain largely unknown. Using human fMRI, we demonstrate that not only higher occipitotemporal but also early retinotopic areas are involved in the perceptual organization and detection of global shapes. Specifically, these areas showed stronger fMRI responses to global contours consisting of collinear elements than to patterns of randomly oriented local elements. More importantly, decreased detection performance and fMRI activations were observed when misalignment of the contour elements disturbed the perceptual coherence of the contours. However, grouping of the misaligned contour elements by disparity resulted in increased performance and fMRI activations, suggesting that similar neural mechanisms may underlie grouping of local elements to global shapes by different visual features (orientation or disparity). Thus, these findings provide novel evidence for the role of both early feature integration processes and higher stages of visual analysis in coherent visual perception.

Humans↗
PubMed2000

Visual function in school-aged children born before 29 weeks of gestation: a population-based study.

The aim of this study was to assess visual function, including visual perception, in a geographically-based population of school-aged children, with a median age of 7.2 years (range 5.1 to 9.3 years), born before 29 weeks of gestation to mothers living in Goteborg, Sweden. Fifty-one preterm children participated in the study, six of whom had known brain lesions. Visual acuity, visual fields, stereoacuity, and visual perception were tested. The Test of Visual Perceptual Skills Revised (TVPS-R, Gardner 1996) was used to measure visual perception, and the results were compared with those of 50 term (control) subjects. Six percent of the preterm children were visually impaired, with a visual acuity of less than 0.3 (6/18), while 42% of all the preterm children and 34% of those without known brain lesions had a total score below the 5th centile of the reference material for the test, compared with 14% of the control subjects. In conclusion, visual-perceptual problems seem to be common among very preterm children and should be screened for and assessed before the children start school.

Child↗
PubMedDate not supplied

Intact visual perceptual discrimination in humans in the absence of perirhinal cortex.

While the role of the perirhinal cortex in declarative memory has been well established, it has been unclear whether the perirhinal cortex might serve an additional nonmnemonic role in visual perception. Evidence that the perirhinal cortex might be important for visual perception comes from a recent report that monkeys with perirhinal cortical lesions are impaired on difficult (but not on simple) visual discrimination tasks. We administered these same tasks to nine amnesic patients, including three severely impaired patients with complete damage to perirhinal cortex bilaterally (E.P., G.P., and G.T.). The patients performed all tasks as well as controls. We suggest that the function of perirhinal cortex as well as antero-lateral temporal cortex may differ between humans and monkeys.

Aged↗
PubMed2004

Impairment in visual and spatial perception in schizophrenia and delusional disorder.

The Judgment of Line Orientation Test, a visuospatial processing task, was administered to normal subjects, to schizophrenic patients and to patients with delusional disorder. Significantly better performance was seen in the normal subjects than in the schizophrenic and delusional patients. Delusional patients, in turn, showed better performance than the schizophrenic patients.

Adolescent↗
PubMed2003

Recurrent episodes of perceptual alteration in patients treated with antipsychotic agents.

Antipsychotics have been sporadically reported to induce the brief recurrent episodes characterized by hypersensitivity of the visual perception, which is known as paroxysmal perceptual alteration (PPA) mainly in Japan. PPA is characterized by hypersensitivity of perception mainly in visual modalities, which could occur in patients treated with antipsychotics. PPA is occasionally known to be accompanied by an oculogyric crisis (OGC). In this study, we examine the prevalence and the characteristics of patients with PPA. Three hundred thirty-eight patients who were treated with antipsychotics and diagnosed with schizophrenia, mood disorders, or neurotic disorders (International Classification of Disease, or ICD-10) were interviewed. We compared the characteristics between subjects with and without PPA. The mean overall prevalence of PPA was 3.25%, which was higher among patients treated with high-potency antipsychotics (3.91%) than in subjects treated with mid-potency or low-potency drugs (1.16%). PPA occurred simultaneously with OGC at the rate of 36.4%. We also found much similarity between PPA and OGC in terms of phenomenology. We suggest that PPA could manifest itself as an undesirable effect of antipsychotics, especially those of high potency. PPA and OGC may a share common underlying mechanism.

Adolescent↗
PubMed1996

A formal theory of feature binding in object perception.

Visual objects are perceived correctly only if their features are identified and then bound together. Illusory conjunctions result when feature identification is correct but an error occurs during feature binding. A new model is proposed that assumes feature binding errors occur because of uncertainty about the location of visual features. This model accounted for data from 2 new experiments better than a model derived from A. M. Treisman and H. Schmidt's (1982) feature integration theory. The traditional method for detecting the occurrence of true illusory conjunctions is shown to be fundamentally flawed. A reexamination of 2 previous studies provided new insights into the role of attention and location information in object perception and a reinterpretation of the deficits in patients who exhibit attentional disorders.

Adult↗
PubMed2001

Postural control: visual and cognitive manipulations.

Numerous questions exist regarding the utilization of sensory information for postural control. Past research has established the possibility that cognitive tasks requiring visual perception may affect the processing of visual information used for postural control. The purpose of this study was two fold: (1) to investigate the effects of varying demands of visual perception and (2) to evaluate the effects of performing a cognitive task on postural control in healthy, young adults (N=30). Three posture-related dependent variables were recorded during the manipulation of two independent variables (eye movement and modality of presentation of a cognitive task). The two levels of eye movement were movement and no movement, while the three levels of modality of presentation were visual, auditory, and none. A 2x3 repeated measures ANOVA was applied to the data to investigate the presence of group differences. Significantly more variability was observed in the no cognitive condition than the visual and the auditory for medial-lateral (M--L) COP variability. Additionally, the eye movement condition revealed significantly greater M--L COP variability than the no eye movement condition. No differences were observed between the visual and auditory conditions for any dependent variable. Therefore, the greatest COP variability was observed in the eye movement and no cognitive condition. Further, an interesting relationship between the measures of COP variability and sway velocity was described.

Adult↗
PubMed1993

[Standardized analysis of visual spatial perception. Construction of the procedure and applications].

Assessment of visuo-spatial perception (VS) in brain-damaged patients. So far, no comprehensive methods for reliable assessment of visuo-spatial deficits after brain damage have been described. The tests usually applied are subtests of intelligence tests, paper-pencil tests or visual-constructive tests which also require motor and planning abilities. Almost all these methods are unsuitable for measuring therapeutic changes and do not reveal specific impairments. The computational method presented here (VS) is suitable for the quantitative assessment of visuo-spatial functions, e.g. subjective visual vertical and horizontal; orientation, length, distance, form and position discrimination as well as line bisection. It can easily be installed on an IBM compatible PC. A clinical standard examination can be performed within 20-30 minutes including numerical and graphical analysis of the results. The method is sensitive for measuring therapeutic changes. Moreover, it offers a wide range of experimental task manipulations for more sophisticated experimental tests.

Attention↗
PubMed1992

Dissociation between mental imagery and object recognition in a brain-damaged patient.

Visual imagery is the creation of mental representations that share many features with veridical visual percepts. Studies of normal and brain-damaged people reinforce the view that visual imagery and visual perception are mediated by a common neural substrate and activate the same representations. Thus, brain-damaged patients with intact vision who have an impairment in perception should have impaired visual imagery. Here we present evidence to the contrary from a patient with severely impaired object recognition (visual object agnosia) but with normal mental imagery. He draws objects in considerable detail from memory and uses information derived from mental images in a variety of tasks. In contrast, he cannot identify visually presented objects, even those he has drawn himself. He has normal visual acuity and intact perception of equally complex material in other domains. We conclude that rich internal representations can be activated to support visual imagery even when they cannot support visually mediated perception of objects.

Adult↗
PubMed2003

Are the results of the Beery-Buktenica Developmental Test of Visual-Motor Integration and its subtests related to achievement test scores?

PURPOSE: Although visual analysis, motor coordination, and visual-motor integration can each affect performance on a test of visual motor integration, previous studies have not reported the relative importance of these components to the relation between visual motor integration and learning readiness, reading, and math. This investigation relates academic achievement in reading and math to performance on the Beery-Buktenica Developmental Test of Visual-Motor Integration (VMI) and its subtests, Visual Perception and Motor Coordination. METHODS: The VMI was administered to 155 children in second through fourth grades (7 to 10 years of age; mean, 8.4 +/- 1.0 years). The Otis-Lennon School Ability Test and Stanford Achievement Test were administered by the school. RESULTS: A significant difference was found in performance on the VMI and Visual Perception and Motor Coordination subtests between children in the upper and lower quartiles in reading (p = 0.020, p < 0.001, and p = 0.027, respectively) and math achievement (p = 0.004, p < 0.001, and p = 0.01, respectively). The VMI standard score was significantly correlated with Stanford total math standard score (p = 0.001) and a trend toward significance was found for Stanford reading score (p = 0.050) while partially controlling for verbal school ability and age. In addition, Visual Perception and Motor Coordination standard scores were significantly related to Stanford math (p < 0.001 and p = 0.005, respectively) and reading score (p = 0.008 and p = 0.027, respectively) after partially controlling for verbal school ability and age. Multiple linear regressions controlling for performance on the VMI and each subtest, as well as age and verbal cognitive ability, showed a significant relation between the Visual Perception subtest score and math achievement. CONCLUSION: Visual perceptual ability should be assessed in children with poor math and/or reading achievement.

Achievement↗
PubMed2000

Cognition. The manifold ways of perception.

One of the great puzzles of visual perception is how an image that is in perpetual flux can still be seen by the observer as the same object. In an informative Perspective, Seung and Lee explain the mathematical intricacies of two new algorithms for modeling the variability of perceptual stimuli and other types of high-dimensional data (Tenenbaum et al., and Roweis and Saul).

Algorithms↗
PubMed2002

Shape perception reduces activity in human primary visual cortex.

Visual perception involves the grouping of individual elements into coherent patterns that reduce the descriptive complexity of a visual scene. The physiological basis of this perceptual simplification remains poorly understood. We used functional MRI to measure activity in a higher object processing area, the lateral occipital complex, and in primary visual cortex in response to visual elements that were either grouped into objects or randomly arranged. We observed significant activity increases in the lateral occipital complex and concurrent reductions of activity in primary visual cortex when elements formed coherent shapes, suggesting that activity in early visual areas is reduced as a result of grouping processes performed in higher areas. These findings are consistent with predictive coding models of vision that postulate that inferences of high-level areas are subtracted from incoming sensory information in lower areas through cortical feedback.

Brain Mapping↗
PubMed1977

Visual movement perception in the cat is directionally selective.

Behavioral experiments show that the visual system of cat contains mechanisms which are selective for direction of stimulus movement. The cat's contrast detection threshold for a drifting grating is unaffected by the addition of a grating moving in the opposite direction; this same pattern of results is found for human observers. The convergence of cat and human psychophysical data suggests that man's brain may hold direction-specific neurons, similar to those known to exist in the cat brain.

Animals↗
PubMed1992

Anisotropic perception of visual angle: implications for the horizontal-vertical illusion, overconstancy of size, and the moon illusion.

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20 degrees to 80 degrees were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5 degrees-30 degrees were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3 degrees-80 degrees were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, theta' = a + b theta + c theta 2 (where theta is the visual angle; theta', the obtained angle; a, b, and c, constants). (2) The linear coefficient b is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficient c is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.

Adult↗
PubMed2004

Audio-visual speech perception is special.

In face-to-face conversation speech is perceived by ear and eye. We studied the prerequisites of audio-visual speech perception by using perceptually ambiguous sine wave replicas of natural speech as auditory stimuli. When the subjects were not aware that the auditory stimuli were speech, they showed only negligible integration of auditory and visual stimuli. When the same subjects learned to perceive the same auditory stimuli as speech, they integrated the auditory and visual stimuli in a similar manner as natural speech. These results demonstrate the existence of a multisensory speech-specific mode of perception.

Association Learning↗