Marginal and extramarginal cortical lesions and visual discrimination by cats.

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Abstract
Cats (75) learned a shape discrimination with zero, 1 or 2 irrelevant cues. They were then subjected to sham operations (n = 34), ablation of the marginal and splenial gyri (n = 9), or lesions in the extramarginal (EM) cortex. The 32 EM cats comprised 4 groups, 3 with small (EM1, n = 9), intermediate (EM2, n = 10), and large (EM3, n = 9) decortications, and a 4th group with both EM lesions and heavy degeneration in the lateral geniculate nucleus (LGN, n = 4). The cats with marginal or extensive extramarginal lesions were severely impaired in shape and size discrimination. Two lines of evidence indicate that their behavioral defects resulted from different neural dysfunctions. The errors made by marginal gyrus cases increased sharply as a function of the number of irrelevant cues present in shape discrimination training; no other group, including group EM3, was affected by this variable. Cats with extramarginal ablations and strong LGN degeneration were no more severely impaired than were subjects with comparable extramarginal damage and little or no LGN degeneration. While the nature of the 2 kinds of deficits remains unclear, they seem parallel to those following posterior cortical lesions in monkeys.