Cortical processing of complex tone stimuli: mismatch negativity at the end of a period of rapid pitch modulation

In this study, synthesised instrumental tones were used to examine human au ditory cortical processes engaged at the end of a period of rapid pitch mod ulation. It was previously [S.J. Jones, O. Longe, M. Vat Pato, Auditory evo ked potentials to abrupt pitch and timbre change of complex tones: electrop hysiological evidence of 'streaming'?, Electroencephalogr. Clin. Neurophysi ol., 108 (1998) 131-142] suggested that the 'change-N1' produced by infrequ ent changes in pitch or timbre of a continuous complex tone represents the activity of a neuronal population topographically distinct from that respon sible for the 'onset-N1' at the beginning of the tone. In the present study a superficially similar negativity was produced when the tone came to rest on a steady pitch after a period of rapid (8-16 changes/s) modulation; its scalp maximum was anterior to that of the two previously identified potent ials but similar to that of the mismatch negativity elicited by discontinuo us tones. By varying the modulation rate the latency was shown to be relati vely constant with respect to the time the next pitch change was expected b ut failed to occur. The largest responses averaging c. 7 mu V were evoked a t the end of modulation sequences which were both rhythmic and repetitive, but a potential was still produced when there was no rhythmic pattern or re petition of individual notes. This response to non-occurrence of an expecte d but not necessarily specified change implies an automatic process for com paring the incoming sound with an extrapolated template of the preceding pa ttern in which timing as well as pitch information is accurately represente d. We suggest this technique offers a robust method for eliciting the misma tch negativity, which may extend the opportunities for electrophysiological investigation of higher auditory processes. (C) 1999 Elsevier Science B.V. All rights reserved.