Readout of Higher-Level Processing in the Discharge of Superior Colliculus Neurons

Abstract: The discharge of neurons in the deeper layers of the superior colliculus (SC) was studied while monkeys performed two visual discrimination tasks that required different amounts of cognitive processing. In a search paradigm the animal's task was to saccade to the location of an odd-colored stimulus located in an array of distractors of uniform color (pop-out visual search). The visual stimuli remained on the screen as the discrimination process distinguished target from distractors. In a choice response task the color of a central cue signaled which stimulus from a previously presented array of colored stimuli was to be the target of a saccade. The stimulus array was turned off well before the central cue was presented. Most neurons showed activity aligned on both the visual input and the motor response in single-target tasks. Many of these same neurons showed additional discharge that was correlated with the required higher-level decision processes in both of these more natural visual tasks. In the case of pop-out search the SC has been shown to be functionally involved in the decision processes. The cue-aligned activity in SC in the choice response task is surprising because no transient visual stimulus appeared in the response field of the neuron.