Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “VISUAL PERCEPTION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 109 records · Page 6Linked to original sources
PubMed1982

Topological structure in visual perception.

Three experiments on tachistoscopic perception of visual stimuli demonstrate that the visual system is sensitive to global topological properties. The results indicate that extraction of global topological properties is a basic factor in perceptual organization.

Form Perception↗
PubMed1984

Mathematical model of visual perception.

A mathematical model of visual perception is presented with the intention of throwing some light on the problem of perceptual invariance. Two types of differential manifolds (receptive and effector) are associated with the repertoire which is the fundamental concept in the model. The elements of the repertoire carry weights which control the input-output relation in the repertoire and which can be modified by a learning process. It is shown that, under reasonable conditions, these repertoires possess good stability properties and can adjust to the various environments to which they may be subjected. In particular cases, it is shown that the stochastic learning process can be considered as deterministic to a first approximation.

Animals↗
PubMed2005

Development of a standardized occupational therapy screening tool for visual perception in adults.

Occupational therapy assessment and treatment of visual perceptual impairments are integral to the rehabilitation of clients following stroke and other acquired brain injuries. Occupational therapists need to identify the nature of visual perceptual performance impairments in order to choose rehabilitation intervention strategies appropriate for remediation of specific problems or to compensate for limitations in daily function. This paper describes the variations in visual perception terminology and occupational therapy approaches to visual perceptual assessment. Limitations of existing assessment tools for visual perception are highlighted in terms of reliability, validity, normative information, length of time to administer, and comprehensiveness in screening for visual perceptual impairment. In response to these limitations, a battery of items, called the Occupational Therapy Adult Perceptual Screening Test (OT-APST) was selected to screen adults comprehensively for impairments of agnosia, visuospatial skills including body scheme and neglect, constructional skills, apraxia, and acalculia. It also includes a subtest to evaluate functional skills directly observed during screening. This new battery has established reliability, validity and age-stratified normative data for adults 16 to 97 years of age. The OT-APST is recommended for use in conjunction with observational assessment of activities of daily living for clients with stroke and acquired brain injury.

Adult↗
PubMed2006

Inertia and memory in ambiguous visual perception.

Perceptual multistability during ambiguous visual perception is an important clue to neural dynamics. We examined perceptual switching during ambiguous depth perception using a Necker cube stimulus, and also during binocular rivalry. Analysis of perceptual switching time series using variance-sample size analysis, spectral analysis and time series shuffling shows that switching times behave as a 1/f noise and possess very long range correlations. The long memory feature contrasts sharply with the traditional satiation models of multistability, where the memory is not incorporated, as well as with recently published models of multistability and neural processing, where memory is excluded. On the other hand, the long memory feature favors the concept of "dynamic core" or coalition of neurons, where neurons form transient coalitions. Perceptual switching then corresponds to replacement of one coalition of neurons by another. The inertia and memory measures the stability of a coalition: a strong and stable coalition has to be won over by another similarly strong and stable coalition, resulting in long switching times. The complicated transient dynamics of competing coalitions of neurons may be addressable using a combination of functional imaging, measurement of frequency-tagged magnetoencephalography and frequency-tagged encephalography, simultaneous recordings of groups of neurons in many areas of the brain, and concepts from statistical mechanics and nonlinear dynamics theory.

Data Interpretation, Statistical↗
PubMed2004

Alcohol intoxication effects on visual perception: an fMRI study.

We examined the effects of two doses of alcohol (EtOH) on functional magnetic resonance imaging (fMRI) activation during a visual perception task. The Motor-Free Visual Perception Test-Revised (MVPT-R) provides measures of overall visual perceptual processing ability. It incorporates different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We used the MVPT-R to study brain activation patterns in healthy controls (1) sober, and (2) at two doses of alcohol intoxication with event-related fMRI. The fMRI data were analyzed using a general linear model approach based upon a model of the time course and a hemodynamic response estimate. Additionally, a correlation analysis was performed to examine dose-dependent amplitude changes. With regard to alcohol-free task-related brain activation, we replicate our previous finding in which SPM group analysis revealed robust activation in visual and visual association areas, frontal eye field (FEF)/dorsolateral prefrontal cortex (DLPFC), and the supplemental motor area (SMA). Consistent with a previous study of EtOH and visual stimulation, EtOH resulted in a dose-dependent decrease in activation amplitude over much of the visual perception network and in a decrease in the maximum contrast-to-noise ratio (in the lingual gyrus). Despite only modest behavior changes (in the expected direction), significant dose-dependent activation increases were observed in insula, DLPFC, and precentral regions, whereas dose-dependent activation decreases were observed in anterior and posterior cingulate, precuneus, and middle frontal areas. Some areas (FEF/DLPFC/SMA) became more diffusely activated (i.e., increased in spatial extent) at the higher dose. Alcohol, thus, appears to have both global and local effects upon the neural correlates of the MVPT-R task, some of which are dose dependent.

Adult↗
PubMed2000

Involuntary orienting to sound improves visual perception.

To perceive real-world objects and events, we need to integrate several stimulus features belonging to different sensory modalities. Although the neural mechanisms and behavioural consequences of intersensory integration have been extensively studied, the processes that enable us to pay attention to multimodal objects are still poorly understood. An important question is whether a stimulus in one sensory modality automatically attracts attention to spatially coincident stimuli that appear subsequently in other modalities, thereby enhancing their perceptual salience. The occurrence of an irrelevant sound does facilitate motor responses to a subsequent light appearing nearby. However, because participants in previous studies made speeded responses rather than psychophysical judgements, it remains unclear whether involuntary auditory attention actually affects the perceptibility of visual stimuli as opposed to postperceptual decision and response processes. Here we provide psychophysical evidence that a sudden sound improves the detectability of a subsequent flash appearing at the same location. These data show that the involuntary orienting of attention to sound enhances early perceptual processing of visual stimuli.

Adult↗
PubMed2002

Does visual perception of object afford action? Evidence from a neuroimaging study.

Positron emission tomography (PET) was used to explore the neural correlates of a potential involvement of motor representation during the perception of visually presented objects with different tasks. The main result of this study was that the perception of objects, irrespective of the task (judgement of the vertical orientation, motor imagery, and silent generation of the noun or of the corresponding action verb), versus perception of non-objects, was associated with rCBF increases in a common set of cortical regions. The occipito-temporal junction, the inferior parietal lobule, the SMA-proper, the pars triangularis in the inferior frontal gyrus, the dorsal and ventral precentral gyrus were engaged in the left hemisphere. The ipsilateral cerebellum was also involved. These activations are congruent with the idea of an involvement of motor representation already during the perception of object and thus provide neurophysiological evidence that the perception of objects automatically affords actions that can be made toward them. Besides this common set of cortical areas, each task engaged specific regions.

Adult↗
PubMed2004

Subnormal visual perception in school-aged ex-preterm patients in a paediatric eye clinic.

PURPOSE: The aim of this study was to assess visual perception at school age of children born preterm with known lesions to the posterior visual pathways or with ophthalmologic signs that might indicate such lesions. METHODS: The study group consisted of 91 patients born before the 37th gestational week. Visual perception was assessed using the TVPS-R (Test of Visual Perceptual Skills - Revised) and a structured interview. In addition, ophthalmologic and orthoptic examinations were performed. RESULTS: On the test of visual perception, 67% of the patients had results below the third percentile of the American reference group. This is to be compared with 10% of Swedish full-term controls. Scores below the third percentile were observed in 87% of the patients with known brain lesions, 48% of those with strabismus without known brain lesion, and 86% of those with reduced visual acuity in the absence of strabismus and known brain lesion. CONCLUSIONS: Reduced visual perception is common among children born preterm who have strabismus and/or reduced visual acuity, as well as in those with known brain lesions. This study emphasises the need to find tools to identify and assess those patients who have visual perceptual problems that may restrict their ability to meet the demands of daily life.

Child↗
PubMed2005

Visual perception and gaze control in judging versus producing phase relations.

We studied visual perception and gaze control in nine participants while they judged the relative phase between two oscillating stimuli (Experiment 1), and while they moved their hand--and therewith a concurrent feedback signal--in-phase or in antiphase with an oscillating stimulus (Experiment 2). As in previous studies, the mean relative phase judgements in Experiment 1 corresponded to the presented phase relations (0 degree, 45 degrees, 90 degrees, 135 degrees, and 180 degrees), whereas their standard deviations followed an inverted U-function of relative phase. The relative phase judgements were hardly affected by the degree of visibility (fully visible, inner parts occluded, outer parts occluded) and the amplitude (5 degrees, 10 degrees, and 20 degrees) of the stimuli. Stimulus-gaze coupling decreased as relative phase increased, and its variability correlated with that of the relative phase judgements. Taken together, task performance and gaze behaviour suggested that the judgement of relative phase might be flexibly based on different variables, rather than a single variable like relative direction of motion. In Experiment 2, the production of the antiphase relation was less stable than that of the in-phase relation. Performance deteriorated when the outer parts of the signals were occluded and when their amplitudes were reduced. Stimulus-gaze coupling was stronger during in-phase than during antiphase tracking and weaker when the signals were partially occluded and when their amplitudes were reduced. Stimulus-gaze coupling at 0 degrees and 180 degrees was stronger in Experiment 2 than in Experiment 1, suggesting that the visual perception of relative phase may benefit from its active production. Overall, the results clearly indicated that visual perception of relative phase and the corresponding gaze control are strongly task-dependent.

Adult↗
PubMed1995

Visual perception and praxis in adults after stroke.

OBJECTIVES: The purpose of this study was to examine the performance of persons with right cerebrovascular accident (RCVA) and persons with left cerebrovascular accident (LCVA) on a variety of measures of praxis and visual perception in order to examine the relative contributions of the left and right cerebral hemispheres to praxis and perception. METHODS: Forty-five subjects, 15 with RCVA, 15 with LCVA, and 15 without CVA (control subjects), were tested on three tests of praxis-praxic production, gesture comprehension, and gesture discrimination-and selected tests of visual perception, including the Judgement of Line Orientation Test, the Motor Free Visual Perception Test, the Hooper Visual Organization Test, and the Line Bisection Test. RESULTS: Subjects in both groups with CVA performed more poorly on all of the tests than did control subjects. The group with LCVA performed most poorly on tests of gesture comprehension and praxis production, whereas the group with RCVA performed most poorly on tests of gesture discrimination and visual perception. CONCLUSION: These findings suggest that both the right and left cerebral hemispheres contribute to different aspects of praxis. Elements of visual perception may be related to gesture comprehension, gesture discrimination, and praxis production in adults who have had stroke. These findings have clinical implications regarding instructional style and perceptual and praxic training.

Aged↗
PubMed1991

Denial of visual perception.

An adult with the diagnosis of cortical blindness, complaining of a complete visual loss of 2 years in duration, was found to have a small preserved visual field and remarkably preserved visual abilities. Although denying visual perception, he correctly named objects, colors, and famous faces, recognized facial emotions, and read various types of single words with greater than 50% accuracy when presented in the upper right visual field. Upon confrontation regarding his apparent visual abilities, the patient continued to deny visual perceptual awareness, typically stating "I feel it." CT indicated bioccipital lesions sparing the left inferior occipital area but involving the left parietal lobe. The denial of visual perception evidenced by this patient may be explained by a disconnection of parietal lobe attentional systems from visual perception. The clinical presentation is described as representing "inverse Anton's syndrome."

Blindness↗
PubMed2002

[Visual perception of Japanese characters and complicated figures: developmental changes of visual P300 event-related potentials].

In order to evaluate developmental change of visual perception, the P300 event-related potentials (ERPs) of visual oddball task were recorded in 34 healthy volunteers ranging from 7 to 37 years of age. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. Visual P300 was dominant at parietal area in almost all subjects. There was a significant difference of P300 latency among the three tasks. Reaction time to the both kind of Kanji tasks were significantly shorter than those to the complicated figure task. P300 latencies to the familiar Kanji, unfamiliar Kanji and figure stimuli decreased until 25.8, 26.9 and 29.4 years of age, respectively, and regression analysis revealed that a positive quadratic function could be fitted to the data. Around 9 years of age, the P300 latency/age slope was largest in the unfamiliar Kanji task. These findings suggest that visual P300 development depends on both the complexity of the tasks and specificity of the stimuli, which might reflect the variety in visual information processing.

Adolescent↗