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 1,711 records · Page 95Linked to original sources
PubMedDate not supplied

Sensory perceptual limitation in schizophrenia.

Sensory perception and selective attention capacity of schizophrenic patients have drawn particular interest. Schizophrenic patients show a peculiar deficit in screening and processing of incoming sensory data. Review of the literature suggests a breakdown in the selective-inhibitory function of attention in schizophrenic patients facing multiple sensory modalities. Although disorganization of attention is a focal point in schizophrenic perception, the influence of memory on the perceptual process deserves further investigation. Distracting sensory stimuli particularly of an auditory nature seem to interfere with visual perception and motor performance in these patients. Avoidance of sensory overload and improving selective attention through psychotherapy though of some therapeutic value, requires further exploration. A case of a young schizophrenic patient exposed to distractible environmental stimuli was presented and discussed.

Adolescent↗
PubMed2000

Mental imagery and perception in hallucination-prone individuals.

College students screened for hallucination-proneness using the Launay-Slade Hallucination Scale (LSHS) were compared on measures of self-report vividness of imagery and on behavioral measures of imagery and perception (visual and auditory). Specifically, we tested the hypothesis whether hallucination-prone individuals would show smaller differences between imagery and perception performance, which may be indicative of increased sensory characteristics of mental images. We replicated earlier findings of higher self-report imagery ratings in the high hallucination-prone group. However, the two groups did not differ on five of six behavioral imagery-perception comparisons. On one visual task, hallucination-proneness was associated with larger imagery-perception differences. Our results reveal a dissociation between the level of subjective experience and the information processing level. Although vividness of mental images may be subjectively associated with mild hallucinatory experiences, we suggest that cognitive processes associated with reality discrimination rather than increased perceptual characteristics of mental images may play a role at the information processing level.

Adult↗
PubMed1988

Shape from texture.

A central goal for visual perception is the recovery of the three-dimensional structure of the surfaces depicted in an image. Crucial information about three-dimensional structure is provided by the spatial distribution of surface markings, particularly for static monocular views: projection distorts texture geometry in a manner tha depends systematically on surface shape and orientation. To isolate and measure this projective distortion in an image is to recover the three dimensional structure of the textured surface. For natural textures, we show that the uniform density assumption (texels are uniformly distributed) is enough to recover the orientation of a single textured plane in view, under perspective projection. Furthermore, when the texels cannot be found, the edges of the image are enough to determine shape, under a more general assumption, that the sum of the lengths of the contours on the world plane is about the same everywhere. Finally, several experimental results for synthetic and natural images are presented.

Form Perception↗
PubMed2006

Visual learning by cue-dependent and cue-invariant mechanisms.

We examined learning at multiple levels of the visual system. Subjects were trained and tested on a same/different slant judgment task or a same/different curvature judgment task using simulated planar surfaces or curved surfaces defined by either stereo or monocular (texture and motion) cues. Taken as a whole, the results of four experiments are consistent with the hypothesis that learning takes place at both cue-dependent and cue-invariant levels, and that learning at these levels can have different generalization properties. If so, then cue-invariant mechanisms may mediate the transfer of learning from familiar cue conditions to novel cue conditions, thereby allowing perceptual learning to be robust and efficient. We claim that learning takes place at multiple levels of the visual system, and that a comprehensive understanding of visual perception requires a good understanding of learning at each of these levels.

Case-Control Studies↗
PubMed2002

The microsystems based visual prosthesis for optic nerve stimulation.

The microsystems based visual prosthesis (MiViP) visual prosthesis generates visual perceptions well below safety and stimulator saturation limits. These perceptions, called phosphenes, are of reasonably small size and are broadly distributed in the visual field. They can thus be used to convey useful visual information. Psychophysical evaluations are being performed in order to assess the implantee's benefits in the use of the MiViP optic nerve visual prosthesis. In a pattern-recognition task, the performance improved regularly with practice with an increasing score and a decreasing delay to recognition. These observations open the way toward an evaluation of general mobility improvement with the portable system. In conclusion, the results obtained so far still support the potential usefulness of the optic nerve visual prosthesis. A low-resolution artificial vision can be expected from the prosthesis after extensive training.

Electric Stimulation↗
PubMed1976

Effects of trace anaesthetic gases on behavioural performance of volunteers.

Nitrous oxide and halothane, in concentrations as low as 50 p.p.m. and 1.0 p.p.m. respectively, caused measurable decrements in performance in psychological tests in healthy male volunteers. Nitrous oxide alone caused similar effects. The functions apparently most sensitive to these low concentrations of anaesthetic agents were visual perception, immediate memory, and a combination of perception, cognition and motor responses required in a task of divided attention to simultaneous visual and auditory stimuli. These effects were absent in subjects exposed to nitrous oxide 25 p.p.m. and halothane 0.5 p.p.m.

Adult↗
PubMed1985

[Mental disorders in patients with unilateral frontal tumors].

Using clinical procedures and psychological tests, the authors examined 72 patients with tumours of the left, and 68 with those of the right frontal lobe of the brain. Tumours of the left frontal lobe were shown to be associated with such manifestations as an impoverishment of motor activity and facial mobility, speech disturbances in the form of efferent motor or dynamic aphasia, slower rate of mental processes, impaired verbal memory, diminished capacity for generalization, difficulty in switching attention to another subject, and inclination toward stereotypy. These disturbances were attended by depressive emotions at the initial, and by the apathoabulic syndrome at the later stages. Tumours located in the right frontal lobe resulted in excessive elation and euphoria, underestimation of the gravity of one's condition and anosognosia, noncritical perception of reality, lack of concentration, diminution in the volume of perception, and a tendency toward confabular additions, which was particularly manifest in the sphere of visual perceptions. The local factor appears to play the principal part in the development of psychic disorders related to the left frontal tumours, whereas in cases of the right frontal tumours, it is the size and the degree of malignancy that matter.

Adult↗
PubMed1994

Visual imagery and visual representation.

Among many controversies in visual neuroscience is whether visual imagery of objects, scenes and living beings is based upon contributions of the early visual areas or depends on hierarchical higher visual areas only, and whether the cortical areas subserving visual imagery are identical to those underlying visual perception. These questions are important for furthering our understanding of vision, since areas active in visual imagery might tell us how the visual cortex represents objects, scenes and living beings. Here, P.E. Roland and B. Gulyás present their hypothesis, based on experimental evidence in man and primates, that the visual areas subserving visual imagery are parieto-occipital and temporo-occipital visual association areas, and that these areas form only a subset of the visual areas engaged in perception. This hypothesis is consistent with the view that objects, scenes and living beings are represented, stored and re-evoked outside the domain of the primary visual cortex and its immediate neighbours.

Animals↗
PubMed2005

Retinal eccentricity effects on reaction time to imagined stimuli.

To cast light on the possible neural substrate of visual imagery we tested normal participants and one hemianopic patient on simple reaction time (RT) to real and imagined visual stimuli. In one experiment participants were to detect as quickly as possible a luminous square presented at one out of two different retinal eccentricities. A well known effect with visual stimuli is that RT is slower for peripheral versus central stimuli. We found that imagined stimuli showed an eccentricity effect similar to that obtained with real stimuli. However, this was not the case in a patient with a hemianopic visual field loss (quadrantanopia) as a result of damage to the optic radiation. Even though the patient showed no difficulty in imaging stimuli in the affected hemifield she did not show an eccentricity effect as was the case in her intact side. In a second experiment, normal participants showed faster RT to stimuli of larger size with either real or imagined stimuli. Overall, these results show that visual perception and imagination share a similar visuotopic organisation that is disrupted following deafferentation of the visual cortex.

Adult↗
PubMed2006

See what you've done! Active touch affects the number of perceived visual objects.

Previous research has shown that visual perception is affected by sensory information from other modalities. For example, sound can alter the visual intensity or the number of visual objects perceived. However, when touch and vision are combined, vision normally dominates--a phenomenon known as visual capture. Here we report a cross-modal interaction between active touch and vision: The perceived number of brief visual events (flashes) is affected by the number of concurrently performed finger movements (keypresses). This sensorimotor illusion occurred despite little ambiguity in the visual stimuli themselves and depended on a close temporal proximity between movement execution and vision.

Adult↗
PubMed2001

Making features similar: comparison processes affect perception.

In this paper, the constructive nature of comparison processes (both similarity- and difference-oriented judgments) is examined through their effects on visual perception. Previous research has shown that comparison processes enhance the tendency to interpret ambiguous objects in the light of the unambiguous objects with which they are compared (Medin, Goldstone, & Gentner, 1993). In the present paper, it is argued that comparison processes affect not only the interpretation of objects, but also their perception. In addition, it is argued that the perceptual effects of similarity-oriented comparison processes differ from those of difference-oriented comparison processes. Accordingly, it is demonstrated that when estimation of an object's size is preceded by similarity-oriented comparisons, the Ebbinghaus illusion practically disappears, whereas prior difference-oriented comparisons tend to enhance the illusion.

Adult↗
PubMed1996

[An unbiased study of the perception of smile and sadness by analysing the integration of emotions].

This article describes a simple and easy-using clinical tool for investigating the visual perception of emotions. The method was validated with healthy persons. On the one hand, the results confirm and sharpen the data of the literature. On the other hand, they enable a precise quantification of the results. Nevertheless, only the perception of the smile and sadness has been studied. Therefore, the extension and validation of this tool to other fundamental emotions is requested. This will enable a simple and easy clinical investigation of troubles of the visual recognition of emotions. On the one hand, for many neurological pathologies: strokes, neurologic disease. On the other hand for psychiatric pathologies: Korsakoff's syndrome, schizophrenia, Alzheimer's disease, other dementias and as on.

Adult↗