Listening to talking faces: motor cortical activation during speech perception

Neurophysiological research suggests that understanding the actions of others harnesses neural circuits that would be used to produce those actions directly. We used fMRI to examine brain areas active during language comprehension in which the speaker was seen and heard while talking (audiovisual) or heard but not seen (audio-alone) or when the speaker was seen talking with the audio track removed (video-alone). We found that audiovisual speech perception activated a network of brain regions that included cortical motor areas involved in planning and executing speech production and areas subserving proprioception related to speech production. These regions included the posterior part of the superior temporal gyrus and sulcus, the pars opercularis, premotor cortex, adjacent primary motor cortex, somatosensory cortex, and the cerebellum. Activity in premotor cortex and posterior superior temporal gyrus and sulcus was modulated by the amount of visually distinguishable phonemes in the stories. None of these regions was activated to the same extent in the audio- or video-alone conditions. These results suggest that integrating observed facial movements into the speech perception process involves a network of multimodal brain regions associated with speech production and that these areas contribute less to speech perception when only auditory signals are present. This distributed network could participate in recognition processing by interpreting visual information about mouth movements as phonetic information based on motor commands that could have generated those movements.