Continuous EEG data were low-pass filtered with a 12 Hz zero phase filter. ERP epochs were time-locked to the onset of the “K” in the GO condition, including a 100 ms baseline preceding the stimulus and 900 ms after it. Trials with no responses (that is errors) were excluded. In the NOGO condition, equivalent 1,000 ms epochs were time-locked to the onset of the “K” and trials with a false alarm response (errors) were excluded. EOG activity such as saccades and blinks were corrected using a regression-based method (Gratton et al. 1983) before baseline correcting by subtracting the average of the 100-ms period before K onset from every sample in the epoch. Individual trials were rejected if any artifacts (±100 μV values) existed in Fz, Cz, or Pz. P3 was identified as the positive peak between 250 and 600 ms at Pz for each subject in the GO condition and Cz for each subject in the NOGO condition, with manual adjustment of the peak locations as necessary. These peak latencies defined the 50 ms search window (±25 ms) for the
