Differential impact of periodic and aperiodic speech-like acoustic signalson magnetic M50/M100 fields

Voiced and unvoiced sounds, characterized by a periodic or aperiodic acoust ic structure, respectively, represent two basic information-bearing element s of the speech signal. Using whole-head magnetencephalography (MEG), magne tic fields (M50/M100) in response to synthetic vowel-like as well as noise- like signals matched in spectral envelope were recorded in 20 subjects. Ape riodic events gave rise to increased M50 concomitant with reduced M100 acti vity as compared to their periodic cognates. Attention toward the auditory channel enhanced the effects of signal periodicity. These data provide firs t evidence that speech-relevant acoustic features differentially affect evo ked magnetic fields as early as the M50 component. Conceivably, the M50 fie ld reflects an ongoing monitoring process whereas the M100 component is bou nd to more specific operations such as detection of signal periodicity. Neu roReport 11:4017-4020 (C) 2000 Lippincott Williams & Wilkins.