AUDITORY-EVOKED POTENTIALS TO ABRUPT PITCH AND TIMBRE CHANGE OF COMPLEX TONES - ELECTROPHYSIOLOGICAL EVIDENCE OF STREAMING

Examination of the cortical auditory evoked potentials to complex tone s changing in pitch and timbre suggests a useful new method for invest igating higher auditory processes, in particular those concerned with 'streaming' and auditory object formation. The main conclusions were: (i) the N1 evoked by a sudden change in pitch or timbre was more poste riorly distributed than the N1 at the onset of the tone, indicating at least partial segregation of the neuronal populations responsive to s ound onset and spectral change; (ii) the T-complex was consistently la rger over the right hemisphere, consistent with clinical and PET evide nce for particular involvement of the right temporal lobe in the proce ssing of timbral and musical material; (iii) responses to timbral chan ge were relatively unaffected by increasing the rate of interspersed c hanges in pitch, suggesting a mechanism for detecting the onset of a n ew voice in a constantly modulated sound stream; (iv) responses to ons et, offset and pitch change of complex tones were relatively unaffecte d by interfering tones when the latter were of a different timbre, sug gesting these responses must be generated subsequent to auditory strea m segregation. (C) 1998 Elsevier Science Ireland Ltd.