All stimuli were presented on a computer monitor using the E-Prime software system (Psychology Software Tools Inc., Pittsburgh, PA). Stimuli were presented on a black screen for 200 ms, followed by a delay varying between 1,000 and 1,100 ms before the next stimulus. Three different types of visual stimuli were presented: (1) standard stimuli; a small hollow white square, (2) target stimuli; a small white X and (3) novel rare nontarget stimuli; different shapes of various colors. Participants were instructed to press a response box button only when they saw target stimuli. Stimuli were presented in a predetermined order, with standard stimuli appearing 210 times, target stimuli appearing 35 times, and rare non-target stimuli appearing 35 times over approximately 6.5 minutes. Each participant was shown an example of the target stimulus before the task began.
