The influence of light drowsiness on the latency and amplitude of P300.

Light drowsiness affected the P300 obtained with a standard auditory oddball paradigm. A simple two-tone discrimination paradigm was used. The frequent nontarget stimuli were 1000 Hz pure tones and the infrequent target stimuli were 2000 Hz pure tones. The subjects were required to press a button whenever infrequent target tones were presented. With light drowsiness, P300 increased in latency and decreased in amplitude, but the counts of infrequent tones remained correct nevertheless. It was concluded that electrophysiological brain function differs in the light drowsy and awake states. In studies on P300, it is essential to rule out light drowsiness to obtain valid P300 amplitudes and latencies.