Saccadic decision making based on uncertain auditory cues in monkey superior colliculus

Saccadic decisions are often based on uncertain auditory cues, which must be evaluated by the auditory or saccadic system and transformed into a motor plan. Relatively little is known about the neural mechanisms that support such saccadic decisions, at least as compared to saccadic decisions based on uncertain visual cues. The superior colliculus (SC) is involved in visual-saccadic decision making and receives auditory-sensory input from multiple brain regions. It is possible, therefore, that the SC is involved in auditory-saccadic decision making in addition to being involved in the evaluation of visual evidence. To examine this possibility, we recorded the activity of SC neurons in a rhesus monkey that was making decisions about where to look based on uncertain auditory cues. On each trial, the monkey fixated a visual stimulus and a sequence of brief, auditory-white-noise bursts was presented in the frontal-horizontal plane. The horizontal position of each burst was drawn from a Gaussian distribution, the mean of which determined the strength of auditory evidence. The monkey’s task was to decide if the mean of the distribution was to the left or right of the frontal midline and to report that decision with a saccade to a visual target. The monkey’s behavior varied systematically with evidence strength: sensitivity increased as the distribution’s mean moved away from the frontal midline. A subset of SC neurons exhibited decision-related activity, meaning that there was a modulation of their activity patterns based on auditory-evidence strength. This suggests that the SC plays a role in the evaluation of uncertain auditory cues when the evaluation of such cues is required for saccade planning. It also suggests a more general role for the SC, and perhaps other oculomotor structures, in the formation of saccadic decisions based on nonvisual sensory input.