Competitive stimulus interactions within single response fields of superior colliculus neurons.

In addition to its role in saccade generation, the superior colliculus (SC) is involved in target selection, saccade selection, and shifting the focus of spatial attention. Here, we investigated the influence of saccade selection on sensory interactions within single response fields (RFs) of SC neurons. One or two differently shaped stimuli were presented within single RFs of SC neurons, and the shape of a centrally located cue indicated whether and where to make a saccade (Go-Go) or whether to make or withhold a saccade (Go/No-Go). We found that, when two stimuli appeared at different locations within a single RF, SC neuronal activity was reduced compared with when a single stimulus appeared in isolation within the center of the RF in both the Go-Go and Go/No-Go tasks. In both tasks, a subsequent cue indicating one stimulus as a saccade target reduced the influence of the second stimulus located within the RF. We found that the time course of the suppression resulting from the two stimuli was approximately 130 ms, a time close to that seen in cortex. Finally, we found that the influence of two stimuli within single RFs of SC neurons changed over time in both the Go-Go and the Go/No-Go tasks. Initially, the neurons averaged the influence of two stimuli. As the trial progressed, the SC neurons signaled only the saccade vector that was produced. We conclude that cues to shift gaze, like attention, modulate the influence of sensory interactions, providing additional support for the linkage between attention and saccade selection.