In the practice session, subjects were instructed to press a key whenever a white triangle pointed either up or down (Go stimulus) and refrain from pressing the key whenever the triangle pointed towards the right or left (NoGo stimulus). A dollar sign ($) appeared on the screen for 200 ms at 1,200 ms after stimulus onset when subjects responded correctly whereas a cross sign (X) appeared on the screen for 200 ms at 1,200 ms after stimulus onset when subjects responded incorrectly. Subjects were instructed that speed and accuracy were equally important for making a correct response. The EEG was recorded during the experimental phase. In this phase, subjects were informed that each correct response would earn a reward. However, each subject received a predetermined fixed amount at the end of the experiment without deductions for errors, although they were not informed of this while performing the task. 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 2,400 ms. Reaction time, Go, NoGo errors, and total correct response percentage were obtained and used for the statistical analysis.
