Elevation of visual pattern discrimination limen in monkeys with total removal of inferotemporal cortex.

Attempts were made to test the validity of the general view that inferotemporal lesions in monkeys do not result in a visual acuity disorder. It was found in the first experiment that monkeys with total removal of the inferotemporal visual area (TIT monkeys) showed a significant elevation of the discrimination limen for visual patterns of reduced sizes even when compared to monkeys with removal of lateral striate cortex (LS monkeys); yet in a food-morsel (raisin) detection test the TIT monkeys performed as well as normal monkeys, although the LS monkeys showed significant deficits. A second experiment was conducted, in which the same subjects were tested with the same patterns as in the first experiment but with the stimulus background changed from the square used earlier to an enlarged disc. While both normal and LS monkeys performed this task easily, the TIT monkeys could not learn the discrimination within the training limit of 1,200 trials. The results suggest that such a marked elevation of the discrimination limen in the TIT monkeys as found in the first experiment is not attributable to a visual acuity disorder, but is explained as due to an impairment of the pattern perception mechanism.