Each subject performed two blocks (80 trials) of a Choice Reaction auditory task using high (1500 Hz) and low pitched (800 Hz) tones, presented every 3 seconds (70 dB; 40 ms duration with an abrupt [2 3s rise time]) in a modified oddball paradigm in which subjects are asked to press a button (right or left) corresponding to the presence of a high or low tone as previously described (Hill et al., 1990; Hill et al., 1995; Steinhauer and Hill, 1993). P300 was evaluated for the infrequent high-pitched tones which occurred on 25% of the trials.
