Procedure

As illustrated in Fig. 1, all trials began with the presentation of a fixation display showing a face outline with either white or black filled-in eye outlines for 750 ms. Next the gaze cue, indicating either a left or right direction was revealed. After a variable time interval, the target demanding a detection response appeared on the left or right of fixation. The gaze cue and the target remained on the screen until a response was made or 2000 ms had elapsed. Approximately 6% of trials contained no target. Response Time (RT) was measured from target onset.

Participants viewed the task on a 16-in CRT monitor from an approximate distance of 57 cm. Before the task, the types of stimuli, the task sequence, and the task were explained to the participants. They were told that the direction of gaze did not predict the location of the target. They were instructed to press the spacebar as quickly and as accurately as possible in response to the target, and to refrain from responding on no-target trials. A total of 612 trials, divided equally across three testing blocks were run. Five practice trials were run at the start. All participants were naïve to the purpose of the study and were fully debriefed after the session.