Brain indices of automatic pattern processing.

The extent to which the auditory system automatically encodes simple auditory patterns was investigated by recording event-related brain potentials (ERPs) to non-attended sounds in subjects reading a book. ERPs were recorded to tones alternating regularly in pitch and to rare breaks in the alternating sequence. In all conditions, breaks in the pattern elicited a right hemisphere dominant fronto-central mismatch negativity (MNN) at a latency of 140-220 ms. The MMN increased in amplitude and decreased in latency with increasing pitch separation and stimulus rate. The results suggest that the processing of auditory patterns occurs automatically and depends on a rapidly fading short-term acoustic memory.