Participants were comfortably seated in front of a computer monitor screen placed 1 m away in a dimly lit, sound-attenuated, radiofrequency-shielded room (IAC Acoustics, Bronx, NY). The EEG was recorded on a Neuroscan System (versions 4.1, 4.2, 4.3, 4.4 and 4.5; Neurosoft, Inc., El Paso, TX) using a 61-channel electrode cap (Electro-cap International, Inc., Eaton, OH) that had electrode placements based on the extended 10–20 International System (Electrode Position Nomenclature; American Clinical Neurophysiology Society, 1991) with the notch filter off. The electrodes were referenced to the tip of the nose, and participants were grounded using an electrode placed on the forehead (frontal midline, 2 cm above nasion). Eye movements were recorded using a supraorbital vertical lead and a horizontal lead on the external canthus of the left eye. Electrode impedance was maintained below 5 kΩ throughout the recording. The continuous EEG signals were recorded and marked with all stimulus, response, and feedback event codes at sampling rates of 512 Hz (16-bit A/D) or 500 Hz (32-bit A/D) depending on the amplifier version, with a bandpass filter set at 0.02 to 100 Hz, and were amplified 10,000 times using a set of amplifiers (SynAmps2, Neurosoft, Inc.).
