The EEG was recorded from 19 scalp locations according to the 10–20 system using an elastic cap with silver-chloride electrodes and a ground electrode on the forehead, with sampling rate 0f 1000 Hz, and high and low-pass filters set at 0.05 and 70 Hz, respectively. The left mastoid served as reference, and an averaged mastoid reference was digitally computed off-line using the right mastoid recording as a separate channel. Vertical electro-oculogram recording was used for eye-blink artifact correction using a regression-based procedure. After screening for artifacts, EEG signals were subjected to 50 Hz low-pass filtering and segmented related to stimulus (Warning, Go, NoGo, and Neutral) into the 2-s segments with a 0.5 s pre-stimulus baseline and 1.5 s post-stimulus interval.
