A visual deficit after superior colliculus lesions in monkeys.

The superior colliculus has been implicated in visual orientation and localization in several mammalian species. To examine this possibility in rhesus monkeys, we trained monkeys to respond to one of six locations signaled by a small light of 5 s duration that was turned off immediately before they were allowed to respond. The locations were directly behind the light. After tectal lesions they continued to perform this task normally, but showed a severe deficit when the duration of the signal was reduced to 1 s. However, when the stimulus remained on throughout the trial and the site of the stimulus and response were further separated, performance of the animals with tectal lesions was normal. We suggest that this deficit in the accuracy of reaching guided by a transient visual stimulus may be related to the role of the superior colliculus in the control of eye movements.