Fig. 1

The stop-signal task. In go trials, after the onset of the start cue (gray circle), the participants had to push a switch (located at the bottom of the monitor) with the dominant hand within 10 s. The switch pressing changed the start cue to a fixation point. If the participants kept the switch pressed for 450 ms, two small targets (white circles) appeared at the left and right sides of the fixation point. If the participant maintained switch pressing for another 300 ms, the fixation point was turned off and a direction cue (horizontal or vertical white bar) was presented at the center of the screen (black background). The horizontal bar instructed touching the right-side target (right go trial) but the vertical bar instructed touching the left-side target (left go trial). The left and right go trials were presented randomly and in the same proportion. The participants had to release the switch and touch the target within a limited time window (900 ms from the onset of the response cue). Failure to touch the screen in this time window was considered as a time-out error. After correct target selection, a feedback was given to the participants (the selected target flashed twice). After an erroneous target selection or early release of the switch, all the items were turned off and a visual error signal (a purple annulus) was shown for 500 ms. Events in the stop trials were similar to those in the go trials; however, after direction-cue onset, a red cross (stop signal) replaced the direction cue. The participants had to maintain pressing the switch after seeing the stop signal. Failure to stop the response in the stop trials (switch release) was considered as an error, and the error signal was shown