The subjects were comfortably seated in front of the computer monitor placed one meter away. EEG was recorded on a Neuroscan system (Version 4.1) using a 61-channel electrode cap which included 19 electrodes of the 10-20 International System and 42 additional electrodes (see Fig. 2). The electrodes were referenced to the tip of the nose and the ground electrode was at the forehead (i.e. 2 cm above the nasion). A supraorbital vertical lead and a horizontal lead on the external canthus of the left eye recorded the electrooculogram (EOG) in order to detect the eye movements. 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). The data were collected at sampling rates of either 256 Hz or 512 Hz, and were resampled at 256 Hz for the sake of uniformity in signal analysis. The continuous EEG was segmented into epochs of 100 ms pre-stimulus (for baseline correction) plus 800 ms post-stimulus of the outcome stimuli. Digital low-pass filtering
