PERIRHINAL CORTEX ABLATION IMPAIRS VISUAL OBJECT IDENTIFICATION

Impairments in both recognition memory and concurrent discrimination l earning have been shown to follow perirhinal cortex ablation in the mo nkey. The pattern of these impairments is consistent with the hypothes is that the perirhinal cortex has a role in the visual identification of objects. In this study we compared the performance of a group of th ree cynomolgus monkeys with bilateral perirhinal cortex ablation with that of a group of three normal controls in two tasks designed to test this hypothesis more directly. In experiment 1 the subjects relearned a set of 40 familiar concurrent discrimination problems; the stimuli in each trial were digitized images of real objects presented in one o f three different views. After attaining criterion they were tested on the same problems using similar, but previously unseen, views of the objects. In experiment 2 the subjects were tested on their ability to perform 10 of these familiar discriminations with each problem present ed in the unfamiliar context of a digitized image of a unique complex scene, The subjects with ablations were significantly impaired on both tasks. These results demonstrate that the role of the perirhinal cort ex is not restricted to memory, and they support the hypothesis that t he perirhinal cortex is involved in visual object identification. We s uggest that the perirhinal cortex is crucially involved in processing coherent concepts of individual objects. A deficit of this nature coul d underlie the pattern of impairments that follow perirhinal cortex da mage in both visual object recognition memory and visual associative m emory.