Neural Mechanisms of Visual Discrimination

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When objects appear in the visual field, animals orient to, discriminate between them and redirect the head to the object of most interest. The cortical pathways involving in visual discrimination were studied by analyzing the deficits following lesions of various cortical areas in trained cats to perform the following visual discrimination task. Cats stand watching a horizontal window of the front wall through which two plastic models of orange and grape were presented, and were required to direct the head to and keep fixating the correct object (orange) after discrimination.We studied which of the two visual systems, geniculate and extrageniculate systems, contribute chiefly in this visual discrimination. Following bilateral ablation of areas 17-18, visual discrimination was little affected. In contrast, after selective unilateral ablation of the lateral suprasylvian visual area (PLLS) among suprasylvian visual areas, cats became unable to discriminate objects in the visual field of … More the lesioned hemisphere, but they compensated deficits by using the visual hemifield of the intact brain.We have previously shown that the superior colliculus (SC) is the brain stem center of head orienting. We studied the cortical areas transmitting commands of head orienting to SC. Following unilateral ablation of the frontal eye fields (FEF), among cortical areas projecting to the SC, caused transientincrease in latencies in orienting directing contralateral to the lesion, but otherwise orienting was normal. However, cats could not discriminate objects in the visual field of the lesioned brain, but become able to compensate by using the brain of the intact side. This suggested that FEF acts as the cortical output after discrimination and sends commands to SC for execution of orienting.We developed techniques to record neural activities from multiple areas simultaneously during visual discrimination. We are now analyzing unit activities in relation to various processes in visual discrimination. Less