title: Phase-locked responses to speech in human auditory cortex are enhanced during comprehension.
abstract: A growing body of evidence shows that ongoing oscillations in auditory cortex modulate their phase to match the rhythm of temporally regular acoustic stimuli, increasing sensitivity to relevant environmental cues and improving detection accuracy. In the current study, we test the hypothesis that nonsensory information provided by linguistic content enhances phase-locked responses to intelligible speech in the human brain. Sixteen adults listened to meaningful sentences while we recorded neural activity using magnetoencephalography. Stimuli were processed using a noise-vocoding technique to vary intelligibility while keeping the temporal acoustic envelope consistent. We show that the acoustic envelopes of sentences contain most power between 4 and 7 Hz and that it is in this frequency band that phase locking between neural activity and envelopes is strongest. Bilateral oscillatory neural activity phase-locked to unintelligible speech, but this cerebro-acoustic phase locking was enhanced when speech was intelligible. This enhanced phase locking was left lateralized and localized to left temporal cortex. Together, our results demonstrate that entrainment to connected speech does not only depend on acoustic characteristics, but is also affected by listeners' ability to extract linguistic information. This suggests a biological framework for speech comprehension in which acoustic and linguistic cues reciprocally aid in stimulus prediction.
authors.affiliation: MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Peelle
authors.forename: Joachim
authors.initials: J
authors.lastname: Gross
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Davis
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001303:Auditory Cortex / Q000502:physiology*; D001931:Brain Mapping; D032882:Comprehension / Q000502:physiology*; D003265:Contingent Negative Variation / Q000502:physiology*; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008037:Linguistics; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D013018:Sound Spectrography; D013060:Speech / Q000502:physiology*; D013067:Speech Perception; D013997:Time Factors; D014825:Vocabulary; D055815:Young Adult