Spectre-temporal analysis of complex tones: two cortical processes dependent on retention of sounds in the long auditory store

Objectives: To examine whether two cortical processes concerned with spectr o-temporal analysis of complex tones, a 'C-process' generating CN1 and CP2 potentials at ct 100 and 180 ms after sudden change of pitch or timbre, and an 'M-process' generating MN1 and MP2 potentials of similar latency at the sudden cessation of repeated changes, are dependent on accumulation of a s ound image in the long auditory store. Methods: The durations of steady (440 Hz) and rapidly oscillating (440-494 Hz, 16 changes/s) pitch of a synthesized 'clarinet' tone were reciprocally varied between 0.5 and 4.5 s within a duty cycle of 5 s. Potentials were re corded at the beginning and end of the period of oscillation in 10 non-atte nding normal subjects. Results: The CN1 at the beginning of pitch oscillation and the MN1 at the e nd were both strongly influenced by the duration of the immediately precedi ng stimulus pattern, mean amplitudes being 3-4 times larger after 4.5 s as compared with 0.5 s, Conclusions: The processes responsible for both CN1 and MN1 are influenced by the duration of the preceding sound pattern over a period comparable to that of the 'echoic memory' or long auditory store. The store therefore app ears to occupy a key position in spectre-temporal sound analysis. The C-pro cess is concerned with the spectral structure of complex sounds, and may th erefore reflect the 'grouping' of frequency components underlying auditory stream segregation. The hi-process (mismatch negativity) is concerned with the: temporal sound structure, and may play an important role in the extrac tion of information from sequential sounds. (C) 2000 Elsevier Science Irela nd Ltd. All rights reserved.