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Matthews, J. (1994). Neurobiology of Visual Perception: A Direct Demonstration of Functional Specialization in Human Visual Cortex. S. Zeki, et al. Journal of Neuroscience. XI, 1991. Pp. 641-649.. Psychoanal Q., 63:392-393.
Psychoanalytic Electronic Publishing: Neurobiology of Visual Perception: A Direct Demonstration of Functional Specialization in Human Visual Cortex. S. Zeki, et al. Journal of Neuroscience. XI, 1991. Pp. 641-649.
Our understanding of visual processing in the cerebral cortex has undergone major revision since the 1970's. The primary visual cortex of the occipital lobe (also called striate cortex, area 17, or V1), which receives topographically arranged binocular input from the retinas via the lateral geniculate nuclei of the thalamus, was traditionally identified as the region of primary visual perception. Visual association areas adjacent to the straite cortex were assumed to function in higher order processing of the visual percepts formed in the striate cortex (V1), for example, comparison with past visual impressions, or the "interpretation" of images. However, since the 1970's, electrophysiological studies largely in the cat and the macaque monkey have demonstrated numerous anatomically distinct areas outside the striate cortex that are involved in the analysis of specific perceptual attributes such as motion, color, or depth perception. Parallel pathways funnel through V1 to these separate areas, with V1 acting as a segregator of signals to relevant extrastriate areas. In
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the macaque brain, for example, color perception occurs in area V4 and motion in area V5.
This study used positron emission tomography (PET) to demonstrate regional subspecialization in human extrastriate visual cortex. PET scanning visualizes dynamic changes in regional blood flow by detecting the changing distribution of trace amounts of inhaled isotopic 15CO2. Localized blood flow is strongly correlated with the intensity of activity, providing a means to assess changes in local activity in response to different types of visual stimuli.
Nine normal male volunteers were studied under two paradigms of visual stimulation, one chosen to emphasize color features and the other chosen for motion features. The color stimulus, a color Land Mondrian figure (nonrepresentational color block pattern), was compared to an isoluminous gray shaded version of the Mondrian, and to the resting condition with eyes closed. The motion pattern, consisting of black squares moving on a white field, was compared to a stationary pattern of squares and to the resting condition. All nonresting conditions demonstrated activation in the striate cortex (co-extensive with areas V1 and V2). The color stimulus also activated a distinct area in the fusiform and lingual gyri of extrastriate cortex (V4), whereas the motion stimulus demonstrated enhanced activity in a region at the occipital-parietal-temporal junction (V5).
These results are consistent with the view that various attributes of the visual scene are analyzed in anatomically discrete regions, and that the subjective perception of a coherent scene requires integration of information from widely separated cortical areas.
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Matthews, J. (1994). Neurobiology of Visual Perception. Psychoanal. Q., 63:392-393