Task-dependent effects of social attention on saccadic reaction times.

Previous research has shown that saccadic reaction times (SRTs) are shorter when a stimulus is flashed on the same side as the observed gaze direction of another individual. The gaze imitation hypothesis contends that observed gaze evokes the preparation of a saccade toward the same direction. Previous studies of this phenomenon have employed pro-saccade tasks in which the instructed saccade is directed toward the stimulus. In agreement with previous findings, we found that SRTs on pro-saccade trials were shorter when the stimulus appeared in the same direction as observed gaze. Here we also included anti-saccade trials in which subjects were required to look-away from a stimulus and toward its mirror position in the opposite visual field. The gaze imitation hypothesis predicts that subjects will have shorter SRTs on anti-saccade trials in which the stimulus appears opposite the observed gaze direction because they will have prepared already a saccade in that direction. However, contrary to the prediction of the gaze imitation hypothesis, we found that subjects had shorter SRTs on anti-saccade trials when the stimulus appeared in the same direction as observed gaze. Moreover, subjects also made more pro-saccade errors on anti-saccade trials in which the stimulus was presented opposite the observed gaze direction. The results of our study indicate that subjects prepared a saccade in the same direction as observed gaze on pro-saccade trials but opposite the observed gaze direction on anti-saccade trials. These findings suggest that the effect of social gaze cues on SRTs is task dependent.