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This chapter focuses on the extrageniculo-striate visual mechanisms. Although the definition of a “visual area” is not always clear, it is supposed that each of them represents specific aspects of visual stimuli. The anatomical connectivity and location of the various areas suggests a grouping of these distributed visual field representations into various visual subsystems. Thus, according to their different afferent organization, two visual systems, a retino-geniculo-striate and a retino-collicularextrastriate visual system were distinguished. These two schemes also stand for two alternative mechanisms of information flow in the cortex, the first one for the model of parallel representation and the second for sequential processing. In primates and especially in man the chapter assumes that the extrastriate visual cortex is functionally more dependent on the striate cortex in that neurons in the prelunate and inferotemporal cortex are reported to become visually inexcitable after ablation or cooling of the striate cortex and in that area 17 lesions in monkey and man appear to be more devastating to visual behavior than in lower mammals.
