Strongly focused attention and auditory event-related potentials.

Effects of selective attention on the auditory event-related potential were studied by delivering two tones in a rapid, randomized sequence. One of the tones was designated as relevant and the other as irrelevant, the subject's task being to discriminate occasional softer tones within the relevant tones. Relevant and irrelevant tones differed from each other either in location (left vs. right ear) or pitch (300 vs. 6000 Hz). In both conditions, relevant tones elicited a larger N1 deflection (peak latency about 120 ms) than did irrelevant tones. In contrast to the exogenous N1 elicited by unattended tones, the scalp distribution of this attentional "N1 effect" did not depend on the stimulated ear and, further, its amplitude was not affected by the frequency of attended tones. These results suggest that the present attention effect was caused, at least mainly, by an endogenous processing negativity rather than by an enhancement of exogenous N1 components.