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Results for “VISUAL PERCEPTION”

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PubMed1988

[Functional and time structure of visual perception in schizophrenia].

A comparative analysis of situations of correct and erroneous perception of visual stimuli and of the dynamics of slow electrical activity of the occipital and frontal cortex has shown that schizophrenia is characterized by specific disorders of the functional and time structure of perception. One of the main signs of these disorders is dysfunction of the frontal cortex at the stages of the synthesis of the perceived information with traces of memory about similar impacts and subsequent categorization of the perceived information.

Action Potentials↗
PubMed2004

Brain areas underlying visual mental imagery and visual perception: an fMRI study.

We used functional magnetic resonance imaging (fMRI) to assess the maximal degree of shared neural processing in visual mental imagery and visual perception. Participants either visualized or saw faint drawings of simple objects, and then judged specific aspects of the drawings (which could only be evaluated properly if they used the correct stimulus). The results document that visual imagery and visual perception draw on most of the same neural machinery. However, although the vast majority of activated voxels were activated during both conditions, the spatial overlap was neither complete nor uniform; the overlap was much more pronounced in frontal and parietal regions than in temporal and occipital regions. This finding may indicate that cognitive control processes function comparably in both imagery and perception, whereas at least some sensory processes may be engaged differently by visual imagery and perception.

Adult↗
PubMed1977

Lateral asymmetries in visual perception: a review of tachistoscopic visual half-field studies.

Experiments using the visual half-field paradigm are reviewed with special reference to the three theories which purport to account for perceptual asymmetries: the left-to-right internal scanning mechanism theory, the direct anatomical access theory, and the attentional bias theory. Recent evidence has clearly shown that the direct anatomical access theory can account for virtually all lateral asymmetries in the perception of verbal and spatial stimuli. The results of the studies reviewed strongly support a model of brain function which suggests that the simultaneous processing of verbal and spatial stimuli does not constrict the attention of either hemisphere. The difficulty in separating the factors of hemispheric processing and stimulus characteristics is discussed. It is suggested that a reliable conclusion about the role of the cerebral hemispheres can only be made when a better description of the operating characteristics of the hemispheres is available.

Attention↗
PubMed1998

On the role of selective attention in visual perception.

What is the role of selective attention in visual perception? Before answering this question, it is necessary to differentiate between attentional mechanisms that influence the identification of a stimulus from those that operate after perception is complete. Cognitive neuroscience techniques are particularly well suited to making this distinction because they allow different attentional mechanisms to be isolated in terms of timing and/or neuroanatomy. The present article describes the use of these techniques in differentiating between perceptual and postperceptual attentional mechanisms and then proposes a specific role of attention in visual perception. Specifically, attention is proposed to resolve ambiguities in neural coding that arise when multiple objects are processed simultaneously. Evidence for this hypothesis is provided by two experiments showing that attention-as measured electrophysiologically-is allocated to visual search targets only under conditions that would be expected to lead to ambiguous neural coding.

Attention↗
PubMed1991

Reappearance of the visual percept after intentional blinking in a patient with Balint's syndrome.

We present a patient with Balint's syndrome who complained of fading of the scenes under visual fixation. When he intentionally blinked, the faded visual percept reappeared. The disappearance of the visual percept may be explained as the result of either unstable visual fixation or of saturation of the visual pathways. The role of blinking in reviving the visual percept may be explained accordingly as causing a refixation of the target under visual fixation or as resetting the visual pathways for visual processing.

Aged↗
PubMed1984

Note on Gibson's direct visual perception.

Gibson's 'ecological approach to visual perception' is shown to be compatible with traditional memory-assisted perception, viz., if it is applied to automatic behavior.

Consciousness↗
PubMed1982

Tachistoscopic visual perception after closed head injury.

Tachistoscopic visual perception was examined in 42 right-handed closed head injury patients and 10 normal controls by determining the duration for recognition of a trigram in central vision and by employing a visual field laterality task. Thresholds did not vary with severity of injury but were significantly longer than those of controls for midly, moderately, and severely injured patients. A nonsignificant right visual field superiority for trigram recognition was exhibited by all groups. Recognition of trigrams in either visual field was impaired in moderately and severely injured patients relative to controls. Possible explanations for these findings are discussed.

Adolescent↗
PubMed2001

What visual perception tells us about mind and brain.

Recent studies of visual perception have begun to reveal the connection between neuronal activity in the brain and conscious visual experience. Transcranial magnetic stimulation of the human occipital lobe disrupts the normal perception of objects in ways suggesting that important aspects of visual perception are based on activity in early visual cortical areas. Recordings made with microelectrodes in animals suggest that the perception of the lightness and depth of visual surfaces develops through computations performed across multiple brain areas. Activity in earlier areas is more tightly correlated with the physical properties of objects whereas neurons in later areas respond in a manner more similar to visual perception.

Brain↗
PubMed1983

Performance of schizophrenic patients on a motor-free visual perception test.

The Motor-Free Visual Perception Test (MVPT) was administered to 15 chronic schizophrenic patients and 15 normal controls, ages 40 to 60, to see whether, perceptual deficits would be found on non-motor tasks. Groups significantly affected performance on the MVPT, as did occupational status. In the schizophrenic group only, efficiency of intellectual functioning was positively related to how well they performed on the MVPT. Age, educational level, and IQ had no significant impact on functioning on this test in either group. The schizophrenic patients made more errors on the more complex operations of the MVPT, and the only significant group differences in percentage of subjects' own errors was in figure-ground. The MVPT may be useful in screening for visual-perceptual deficits in adult schizophrenic patients.

Adult↗
PubMed1989

[Visual perception in normal children and adults II. Correlation between dominance of visual field and dominance of the eye].

To clarify more precisely about the correlation between the dominance of visual field and dominance of the eye, tachistoscopic examination was performed on 48 normal adults; 24 males and 24 females, and 24 right-handed and 24 left-handed subjects. The mean of the time of exposure was less than 4.5 msec. The time of exposure was independent of handedness, dominance of the eye, sex, or the type of stimulus. Four right-handed and four left-handed subjects showed dominance of the left visual field for the A value, suggesting no correlation between handedness and dominance of the visual field. However, six of those eight subjects were found to have dominance of the left eye for the A value, and all seven subjects with dominance of the left visual field for the D value showed dominance of the left eye (chi 2 = 16.39, p less than 0.001). It was concluded that dominance of the eye was significantly correlated with visual field. It is therefore important to examine dominance of the eye as well as dominance of the visual field for evaluation of cerebral dominance with regard to visual perception.

Adult↗
PubMed2002

Object-based and action-based visual perception in children with spina bifida and hydrocephalus.

Children with spina bifida and hydrocephalus (SBH) have long been known to have difficulties with visual perception. We studied how children with SBH perform 12 visual perception tasks requiring object identification, multistable representations of visual space, or visually guided overt actions. Four tasks required object-based processing (visual constancy illusions, face recognition, recognition of fragmented objects, line orientation). Four tasks required the representation of visual space in egocentric coordinates (stereopsis, visual figure-ground identification, perception of multistable figures, egocentric mental rotation). Four tasks required the coupling of visual space to overt movement (visual pursuit, figure drawing, visually guided route finding, visually guided route planning). Effect sizes, measuring the magnitude of the difference between SBH children and controls, were consistently larger for action-based than object-based visual perception tasks. Within action-based tasks, effect sizes were large and roughly comparable for tasks requiring the representation of visual space and for tasks requiring visually guided action. The results are discussed in terms of the physical and brain problems of children with SBH that limit their ability to build effective situation models of space.

Adolescent↗
PubMed2005

The developmental test of visual perception-2 normative study on the visual-perceptual function for children in Hong Kong.

This research study intended to investigate the visualperceptual performance of children in Hong Kong by comparing them to the accepted norms on the Developmental Test of Visual Perception-2nd edition. The research examined whether there was significant difference in child's gender, age, and grade. The normative study recruited two hundred and eight-nine children between the ages of 6 and 7 in normal primary schools in Hong Kong. Results indicated that there was a ceiling effect in eye-hand coordination, position in space and spatial relations subtests. Grade differences were found to be significant in all subtests except eye-hand coordination and visual-motor speed. On the other hand, there were no statistical difference in the test scores between boys and girls except on copying and figure-ground subtests. It is concluded that there is a strong need to ensure that norms for visual-perceptual tests are appropriate for the specific cultural groups being assessed.

Child↗
PubMed1990

A role of amygdala in visual perception and cognition in macaque monkeys (Macaca fuscata and Macaca mulatta).

To elucidate the role of the amygdala in visual perception and cognition, the effects of ablations of the amygdala and inferotemporal cortex on several visual tasks were compared with each other, and also the distribution patterns of the projections between them were investigated. The findings indicate that the inferotemporal cortex plays a critical role in visual perception, cognition and memory, whereas the amygdala is involved fundamentally in controlling emotional and motivational behavior. However, the amygdala is concerned with vision in the following ways: It receives neutral visual information highly processed in the visual cortex, invests the information with emotional and motivational significance through interactions with the cortical and subcortical systems of emotion and motivation, and then it returns the information coded to the visual areas to be re-processed; to be consciously perceived in area TEO, and to be meaningfully cognized, recognized and memorized in areas TE and TEG. Therefore, two channel model regarding the mechanism of visual information processing in the inferotemporal cortex is proposed: A first channel is concerned with processing neutral information, while the second one, with processing meaning information coded emotionally and motivationally in the amygdala. In addition, the present studies demonstrate that area TEG, which is cytoarchitecturally a transitional area between areas TE and TG and whose functional significance has remained unclear, is involved significantly in visual cognition rather than visual perception.

Agnosia↗
PubMed2006

Comparison of Bayesian and empirical ranking approaches to visual perception.

Much current vision research is predicated on the idea--and a rapidly growing body of evidence--that visual percepts are generated according to the empirical significance of light stimuli rather than their physical characteristics. As a result, an increasing number of investigators have asked how visual perception can be rationalized in these terms. Here, we compare two different theoretical frameworks for predicting what observers actually see in response to visual stimuli: Bayesian decision theory and empirical ranking theory. Deciding which of these approaches has greater merit is likely to determine how the statistical operations that apparently underlie visual perception are eventually understood.

Bayes Theorem↗
PubMed1999

An optimal estimation approach to visual perception and learning.

How does the visual system learn an internal model of the external environment? How is this internal model used during visual perception? How are occlusions and background clutter so effortlessly discounted for when recognizing a familiar object? How is a particular object of interest attended to and recognized in the presence of other objects in the field of view? In this paper, we attempt to address these questions from the perspective of Bayesian optimal estimation theory. Using the concept of generative models and the statistical theory of Kalman filtering, we show how static and dynamic events occurring in the visual environment may be learned and recognized given only the input images. We also describe an extension of the Kalman filter model that can handle multiple objects in the field of view. The resulting robust Kalman filter model demonstrates how certain forms of attention can be viewed as an emergent property of the interaction between top-down expectations and bottom-up signals. Experimental results are provided to help demonstrate the ability of such a model to perform robust segmentation and recognition of objects and image sequences in the presence of occlusions and clutter.

Attention↗
PubMed2005

Visual perception of surface wrinkles.

To study the relationship between visual perception of magnitude of wrinkles and geometrical parameters of surfaces, four potentially relevant parameters of the surface profile were considered: the variance (sigma2), the cutting frequency (Fc), the effective disparity curvature (Dce) of the wrinkled surface over the eyeball distance of the observer, and the frequency component of the disparity curvature (Dcf). Analysis of garment seams with varying amount of pucker showed that, while the logarithm for each of these four parameters has a strong linear relationship with the visually perceived magnitude of wrinkles, following the Fechner Law, the effective disparity curvature (Dce) and the frequency component of the disparity curvature (Dcf) with visual perception appeared stronger. This modeling may be an objective method for measuring magnitude of surface wrinkles.

Clothing↗