NEURAL CODING OF VISUAL STIMULI

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We recorded the activity of single neurons in the primary visual cortex, the first cortical stage of visual processing, and inferior temporal cortex, the last cortical stage, to study the mechanisms underlying visual perception. When neurons were analyzed as communication channels carrying information in their responses, the response patterns seen could only be represented as the sum of several (3-6) simultaneous, independent patterns of activity. These activity patterns were analyzed as temporal code, and this code was found to contain more information than that conveyed by the response strength, the usual measure of neuronal response. The proportion of information carried in the temporal code increases steadily as one proceeds from the periphery through progressively more and more central statious of the visual system. Neurons recorded from inferior temporal cortex while monkeys perform a simple visual memory task, matching-to- sample, carry information differentiating the physical dimensions of the stimuli as well as their meaning, i.e., their whether each is the sample, the matching, or the nonmatching stimulus. Each member of a neuronal pair recorded simultaneously from a single electrode in both primary and inferior temporal cortex is independent of the other member, i.e., their information adds. This suggests that local processing is carried out by combining independent neuronal analyses of the stimulus being viewed.