Stimulus-dependent form discrimination deficits in cats with superior colliculus lesions.

Previous studies have shown that cats with damaged superior colliculi are slower than normal in learning new visual discriminations based upon shape but show no losses in retention of discriminations learned prior to the tectal lesion. To elucidate the possible mechanisms producing this deficit, the rate at which cats with superior colliculus lesions learned to discriminate between targets differing either in (1) global features, or (2) a single, uniquely localized, feature was measured. Cats were first tested with problems shown in earlier studies to produce acquisition deficits and those with superior colliculus lesions showed the expected deficits. The rate of acquisition of form discriminations based on global stimulus features in these cats was, however, comparable to normals and sham-operated controls. When tested with targets differing only in a single, localized feature, acquisition of the discrimination was severely impaired compared to controls. The observed deficits did not depend upon damage to pretectum or total ablation of the superior colliculus. The results support the view that the superior colliculus is a major contributor to visuomotor integration (e.g. foveation of salient stimulus features), and that such visuomotor behavior is an important determinant in form discrimination learning.