EEG was recorded on a Neuroscan system (Version 4.1) using a 61-channel electrode cap (see Fig. 3), referenced to the tip of the nose with a ground electrode at the forehead. A supraorbital vertical lead and a horizontal lead on the external canthus of the left eye recorded the electro-oculogram (EOG). Electrode impedance was maintained below 5 kΩ. The EEG signals were recorded continuously with a bandpass at 0.02–100 Hz and amplified 10,000 times using a set of amplifiers (Sensorium, Charlotte, VT). EEG segments that exceeded ±75 μV threshold were rejected as artifacts. The grand averaged ERPs of each individual were also screened visually for further artifact rejection. Although the entire experiment consisted of two identical blocks, the analysis was done on all trials by combining the trials from both blocks. The statistical analyses were performed on the amplitude and latency data of ORN and ORP components.
