Abstract
Abstract: With each shift in gaze the numerous objects in the visual scene impinge on new retinal locations, to only one of which can the ensuing eye movement be directed. We examined the role various cortical structures play in this process of target selection by determining how subthreshold electrical microstimulation can bias saccadic eye movements made to one of two targets presented in the visual field. Electrical stimulation (80ms, 200Hz) was delivered while monkeys had to execute an eye movement to either of two targets, one of which was centered within the receptive or motor field of the stimulated neurons. Subthreshold stimulation in the frontal (FEF) and medial eye fields (MEF) always increased the probability of directing the eyes to the target in the motor field. Stimulation at many sites in V1, V2, and the intraparietal sulcus (LIP) unexpectedly decreased the probability of executing saccades to the target in the receptive field. Stimulation of some regions of LIP delayed saccade initiation. In V4 stimulation was ineffective. The results identify five computations necessary for saccade initiation: (1) determine what the objects are in the scene, (2) select one object to look at, (3) decide which objects not to look at, (4) assess where the objects are in space, and (5) decide when to initiate the eye movement. Areas V1, V2, LIP are involved in 1, 2, 3, and 4; LIP, in addition, is involved in #5. The FEF and MEF are involved in 2 and 4.