Figure 1.

Trial displays for the countermanding saccade task. Each trial began with the fixation of a central fixation point (FP) for a variable interval after which it disappeared and a target (T) simultaneously appeared, either in the response field of the neuron or in the opposite hemifield. In the CONTROL trials, monkeys were rewarded for responding with a single targeting saccade (left). On a fraction of interleaved trials (right), the fixation point reappeared after a variable delay (SSD) and acted as a stop signal instructing the monkeys to withhold saccade initiation. In these STOP trials, they were rewarded for countermanding the planned movement and maintaining fixation on the fixation point (canceled STOP trials). No reward was delivered if they responded with a targeting saccade (noncanceled STOP trials). The dotted circle and arrow indicate current gaze position and saccade vector during each interval, respectively.