Contrasting effects of lateral striate and superior colliculus lesions on visual discrimination performance in rhesus monkeys.

Abstract

Rhesus monkeys [Macaca mulatta] with lesions of lateral striate cortex, monkeys with superior colliculus lesions and unoperated monkeys were tested for retention of a preoperatively acquired pattern discrimination. The 3 groups of monkeys were then tested in 2-choice, color discrimination tests, one involving varying degrees of stimulus-response (S-R) separation and the other, administered several months later, involving various directions of S-R separation. The monkeys were also tested in a series of 2-choice pattern discriminations; following each they were tested for relearning when the patterns were masked with bars or circles. The monkeys with lateral striate lesions were moderately retarded in retention of the pattern discrimination; those with superior colliculus lesions were not. The monkeys with colliculus lesions, but not those with lateral striate lesions, were impaired in both S-R separation tests; their deficit was not transient or solely due to a difficulty in shifting the gaze in one direction. The lateral striate monkeys, unlike those with colliculus lesions, were deficient in relearning discriminations between masked patterns. The superior colliculus and striate cortex may be involved in 2 different aspects of attention: respectively, shifting attention (and orientation) from one spatial locus to another and maintaining attention on fixated stimuli. Alternative interpretations of the effects of the lesions, based on their retinotopic loci, are discussed.