Fig. 1.

Go/nogo task. On each trial, a fixation asterisk was presented for 100 ms, followed by an uppercase letter for 500 ms, and then a 500 ms blank screen. Participants were required to respond within 1000 ms to frequently presented “go” stimuli (any letter other than “X”) and withhold responses to infrequently presented “nogo” stimuli (the letter “X”). Go/nogo stimuli were presented in a 70/30 ratio in a pseudo-random order, with all nogo trials preceded by at least one nogo trial; each experimental block was initiated by a stream of an additional 20 consecutive go trials in order to build up a prepotent response tendency towards go stimuli.