The electroencephalogram (EEG) was recorded from 64 tin electrodes fixed in a stretch-lycra cap (ElectroCap, Eaton, OH) placed on the scalp in standard locations (American Encephalographic Society, 1994) and referenced to the right mastoid; an average mastoid reference was derived offline. Impedance was kept below 8 kΩ at all locations. EEG signals were amplified with Synamps2 amplifiers (Compumedics-Neuroscan, Charlotte, NC), sampled at 1000 Hz and filtered online at 0.05 to 40 Hz. Ocular artifacts were removed from the EEG signal off-line using a regression-based procedure (Semlitsch, Anderer, Schuster, & Presslich, 1986), after which a bandpass filter of 1 to 15 Hz was applied before response-locked epochs of −400 to 600 ms were derived. After artifact removal and rejection, EEG data were averaged according to participant, electrode, and stimulus conditions. The ERN and Pe components were quantified as the average amplitudes occurring 0–150 ms postresponse, and 150–250 ms postresponse, respectively, at all scalp electrodes.
