Inhibitory processes mediate saccadic target selection.

Observers (N = 3, all males, M age = 30.7 yr.) were presented pairs of visual targets and instructed to fixate one as quickly as possible. The resulting saccades were of two types; bistable saccades accurately acquired one of the targets whereas averaging saccades landed at intermediate locations. The hypothesis was that averaging saccades result from a pooling of afferent activity prior to selection of saccadic direction and amplitude (i.e., coactive parallel processing) and that bistable saccades would show evidence of response competition between incompatible motor programs within a parallel architecture. Analysis of the distributions of saccadic reaction times showed that in all cases saccadic responses to double targets were too slow to be consistent with either the channel summation or any form of race model. Results indicate that inhibitory interactions operate during the selection of a target for a saccadic eye movement.