Effects of posterior parietal and frontal neocortical lesions in the squirrel monkey.

Brightness discrimination, three forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were separated (SSP), delayed response, form discrimination, and three forms of a spatial pattern discrimination in which the essential cue and site of reinforcement were identical (ISP) were given, in the order mentioned, to two groups of squirrel monkeys with frontal lesions were impaired on delayed response, and those with parietal lesions were impaired on form and SSP discriminations. Neither group was impaired on brightness discrimination. The results confirm and extend previous findings by other investigators that the posterior parietal cortex of nonhuman primates is critically involved in visually guided spatial discriminations when the primary cue and the site of reinforcement are separated.