title: Lip movements entrain the observers' low-frequency brain oscillations to facilitate speech intelligibility.
abstract: During continuous speech, lip movements provide visual temporal signals that facilitate speech processing. Here, using MEG we directly investigated how these visual signals interact with rhythmic brain activity in participants listening to and seeing the speaker. First, we investigated coherence between oscillatory brain activity and speaker's lip movements and demonstrated significant entrainment in visual cortex. We then used partial coherence to remove contributions of the coherent auditory speech signal from the lip-brain coherence. Comparing this synchronization between different attention conditions revealed that attending visual speech enhances the coherence between activity in visual cortex and the speaker's lips. Further, we identified a significant partial coherence between left motor cortex and lip movements and this partial coherence directly predicted comprehension accuracy. Our results emphasize the importance of visually entrained and attention-modulated rhythmic brain activity for the enhancement of audiovisual speech processing.
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Hyojin
authors.identifier: 0000-0002-7527-8280
authors.initials: H
authors.lastname: Park
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Christoph
authors.identifier: 0000-0001-7362-5704
authors.initials: C
authors.lastname: Kayser
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Gregor
authors.initials: G
authors.lastname: Thut
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Joachim
authors.identifier: 0000-0002-3994-1006
authors.initials: J
authors.lastname: Gross
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D058256:Brain Waves; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008046:Lip / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement; D011597:Psychomotor Performance; D013065:Speech Intelligibility; D014793:Visual Cortex; D055815:Young Adult
keywords: electroencephalography; human; language; lip movements; magnetoencephalography; neuroscience; oscillations; speech