AUDITORY EVENT-RELATED POTENTIALS DISSOCIATE EARLY AND LATE MEMORY PROCESSES

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented soun ds, 20% of which were presented once and 80% were repeated. Of the rep eated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2-6 inter vening sounds (4-12 sec; long delay repetition). Subjects were instruc ted to indicate whether they had heard the sounds before by pressing a ''yes'' or ''no'' button. The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonge d latency P3 component while the short delay repetition stimuli elicit ed no N4 component and an earlier latency P3 component. Subjects' resp onses were faster and more accurate for short delay repetition. All st imuli generated a sustained frontal negative component (SFN). These da ta indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long del ay repetition stimuli may index activation of a neocortical template m atching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.