Stimuli consisted of a fixation cross (+) presented in the centre of a computer screen, which was then followed by either a "Go" stimulus (e.g. a square shape) or a "No-go" stimulus (e.g. diamond shape). Subjects were instructed to perform a button press to the “Go”, but to withhold a response to the “No-go” stimulus. Participants were then informed on the accuracy of their response via the fixation cross following the Go or No-go stimulus, which remained the usual white colour to correct responses, but changed to a red colour on the incorrect responses. Subjects were then instructed to respond fast enough to avoid the red fixation cross. Those in the HI group were required to respond within 300 ms of the Go stimulus, while the LI group were required to respond within 500 ms. All stimuli were equal in duration and intensity. The total number of stimulus presented was 100, with 30% of these being No-go stimuli.
Data Extraction
Behavioural measures such as omission errors to Go stimuli (i.e. a missed press to a Go stimulus) and commission errors (i.e. a press to a No-go stimulus) were calculated. ERPs were derived at Fz (the frontal midline site). ERPs were calculated to Go and No-go stimuli separately, and the N1 and N2 components in each ERP was quantified in terms of amplitude (relative to a 100 millisecond baseline). ERP epochs containing blinks or errors were excluded from averaging.
Data