a NoGo stimulus within 1200 ms from stimulus onset or did not press the key hard enough and/or within 100-500 ms of stimulus onset for a Go stimulus, a cross sign (X) appeared on the screen for 200 ms at 1200 ms after stimulus onset. Subjects were instructed that speed and accuracy were equally important for making a correct response. The probabilities of occurrence of Go and NoGo stimuli were equal (50/50), and the order of stimulus presentation was randomized. The inter-trial interval was 2400 ms.
