Listening to talking faces: motor cortical activation during speech perception

Area of Science:

• Neuroscience
• Cognitive Science
• Speech Perception

Background:

• Neurophysiological studies indicate that understanding others' actions involves neural circuits used for direct action production.
• Speech perception is a complex process influenced by both auditory and visual information.

Purpose of the Study:

• To investigate brain activity during audiovisual, audio-only, and video-only speech perception using functional magnetic resonance imaging (fMRI).
• To identify neural networks involved in integrating visual speech cues with auditory information.

Main Methods:

• fMRI scans were conducted on participants during three conditions: audiovisual speech, audio-alone speech, and video-alone speech.
• Participants listened to and/or watched stories presented by a speaker.

Main Results:

• Audiovisual speech perception activated a network including motor areas (premotor cortex, primary motor cortex) and sensory areas (somatosensory cortex, cerebellum) related to speech production.
• Activity in premotor cortex and posterior superior temporal gyrus/sulcus correlated with the visual clarity of phonemes.
• These speech production-related areas showed significantly less activation in audio-alone and video-alone conditions.

Conclusions:

• Integrating visual speech movements into perception recruits multimodal brain regions associated with speech production.
• These findings suggest that visual speech information is processed through a network that interprets mouth movements as phonetic information via motor commands.
• The study highlights the contribution of motor and sensory systems to speech perception, particularly when visual cues are available.