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Magnetic Brain Activity Tracing the Perceived Speech Signal Regarding Envelope, Syllable Onsets, and Pitch Periodicity

Continuous speech evokes electrophysiological brain activity phase-locked to the speech envelope (ENV), resembling the N100 responses to single acoustic events. Using magnetoencophalography (MEG), the present study investigated further MEG components that directly reflect acoustic properties of continuous speech signals, i.e., a derivate of the envelope that can be taken as a physical marker of syllable onsets (SYL), and a pitch periodicity signal (PIT) obtained by bandpass filtering of the rectified speech signal. The participants (n = 10) listened to natural or formantsynthesized speech at a moderately fast or ultrafast speaking rate. As expected, the MEG crosscorrelation function with ENV showed a rightlateralized M100-like response with a source in the region of the central auditory system. Regarding the SYL derivate, in addition to auditory M50/M100-like responses a late, more anterior M50-like source component could be isolated. The cross-correlate of MEG data with the PIT derivate of the speech signal comprised multiple peaks of alternating polarity bound to a central-auditory source. The amplitude of the peaks in the crosscorrelation functions depended upon speech rate and signal type (natural versus synthetic).