Abstract
We rely on our ability to inhibit prepotent reactions to our surroundings and execute appropriate behaviors. Both antisaccade and countermanding tasks have been used extensively to test theories about inhibitory control within the primate saccade system. Although it is believed that each task may tap similar neural mechanisms of inhibition, to date there have been no direct comparisons. Here, we compared performance on antisaccade and countermanding saccade tasks in the same group of subjects to test the hypothesis that a common mechanism underlies inhibiting saccades in both tasks. We predicted that subjects with strong inhibition in one task should show high inhibition in the other task. In both tasks, the predominant response was to make a saccade toward a salient visual cue. In the antisaccade task, subjects were instructed to make a saccade away from the cue, which required that one first inhibit a saccade to the cue. In the countermanding task, subjects were instructed to cancel a planned saccade when an auditory stop signal was emitted at various delays following the appearance of the visual cue, i.e., stop signal delays (SSD). Subjects' eye movements were monitored to measure their ability to suppress unwanted saccades, saccade initiation times, and a latent variable called the stop signal reaction time (SSRT). The SSRT is thought to index the time one needs to inhibit a saccade. In the countermanding task, stop-success rate declined as SSD increased. In the antisaccade task, the probability of successfully generating an antisaccade increased with increasing initiation times. Moreover, estimates of SSRT from the countermanding task correlated with one's ability to successfully generate antisaccades. Our results provide strong evidence that a common mechanism underlies saccade suppression in both tasks.