Schematic representations of the stimulus display sequence and the oculomotor task in the Go-Only sessions and in the Go/NoGo sessions. Every trial started with the fixation of a small central cross. Two squares, targets for the saccade, were then presented simultaneously on both left and right sides of the fixation cross. The direction of the saccade was shown by the pointing of an arrowhead which then appeared in place of the fixation cross. In the Go-Only sessions, the subjects made a saccade to one target in each trial. The Go/NoGo sessions contained trials in which the arrowhead pointed downward instructing the subjects to hold the fixation.