Lip movements entrain the observers' low-frequency brain oscillations to facilitate speech intelligibility

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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.

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Hyojin Park

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom

For correspondence
Hyojin.Park@glasgow.ac.uk

Competing interests
The authors declare that no competing interests exist.
Christoph Kayser

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Gregor Thut

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Joachim Gross

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom

Competing interests
The authors declare that no competing interests exist.

Ethics

Human subjects: This study was approved by the local ethics committee (CSE01321; University of Glasgow, Faculty of Information and Mathematical Sciences) and conducted in conformity with the Declaration of Helsinki. All participants provided informed written consent before participating in the experiment and received monetary compensation for their participation.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.