EEG data were analyzed offline with Neuroscan 4.5 Scan software in the following order. All EEG channels were referenced offline to linked mastoids. Data were band-pass-filtered using a zero phase shift finite impulse response (FIR) filter between 0.3 and 30 Hz. Vertical and horizontal ocular artifacts were reduced using the ocular artifact reduction algorithms from Neuroscan 4.5. When present, the EKG noise reduction algorithm from Neuroscan 4.5 was used to reduce these artifacts. All data were then visually inspected and any epochs with remaining artifact (muscle, movement, etc.) were manually rejected. Because the N2 is observed following the stimulus presentation, this potential was time-locked to the stimulus (stimulus-locked). By contrast, the ERN and CRN occur following a response, so these potentials were time-locked to the response (response-locked). Stimulus-locked ERPs were epoched from 400 ms before to 800 ms following the stimulus. Response-locked ERP epochs spanned from 200 ms before to 600 ms following the response. To improve the visual presentation of the data, all epoched waveforms were then band-pass-filtered using a zero phase shift FIR filter between 1 and 12
