All recordings were digitally re-sampled offline at 256 samples per second with 0.3-45 Hz band pass filter in order to control for the DC drifts and AC power artifacts in the waveform. The EEG segments were divided into epochs of 1,625 ms (187.5 ms pre- and 1,437.5 ms post stimulus). All epochs exceeding ±100 μV amplitude were automatically excluded from further processing. Each participant's successful trials were averaged based on task conditions and visually inspected using a display program to further eliminate those trials that show evidence of any kind of artifact. Only artifact-free correct trials were considered for the analysis. In order to reduce within subject variability due to the effect of averaging on the computed power values for each participant, a minimum of 15 and a maximum of 25 artifact-free correct trials out of a maximum of 50 trials in each task condition (Go and NoGo) was taken for further analysis. If there were more than 25 artifact-free correct trials in a condition, 25 trials were selected randomly from the pool. The S-transform method was used to obtain
