Fig. 1.

Example trial of the main task. Each trial comprised 2 stimulus presentations of 500 ms each. Either the same image was presented twice (repeat trial) or 2 different images were presented (nonrepeat trial). Image presentations were separated by 1 of 5 interstimulus intervals (ISIs; 50, 100, 200, 500, or 1,000 ms). Participants were instructed to fixate on a small gray disk in the center of the screen (see inset) and performed a 1-back task on digits (0 to 9), which were shown within the fixation disk at a presentation rate of 1.5 Hz. Trials were separated by a variable intertrial interval (ITI), during which only the fixation disk and digits were shown.