The Motor Network Reduces Multisensory Illusory Perception.

Area of Science:

• Neuroscience
• Cognitive Science
• Speech Perception

Background:

• The McGurk effect demonstrates how visual speech information influences auditory perception.
• The role of the motor network in multisensory speech processing and illusion avoidance is not well understood.

Purpose of the Study:

• To investigate the functional contribution of the motor network to the McGurk effect using fMRI and TMS.
• To identify the specific motor areas and their temporal dynamics involved in processing audiovisual speech stimuli.

Main Methods:

• Functional magnetic resonance imaging (fMRI) to observe brain activity during audiovisual speech tasks.
• Transcranial magnetic stimulation (TMS) to modulate activity in specific motor cortex areas (lip and foot).
• Event-related design analyzing responses to congruent and incongruent audiovisual stimuli.

Main Results:

• fMRI revealed bilateral inferior frontal gyrus (IFG) activation in incongruent trials, with left IFG activity negatively correlated with McGurk effect perception.
• Enhanced effective connectivity was observed between the left IFG and precentral gyri during incongruent trials.
• TMS applied to the primary motor cortex (M1) lip area reduced the McGurk effect, specifically within a 100 ms pre- to 200 ms post-auditory onset window.

Conclusions:

• The motor network, particularly the IFG and M1 lip area, plays a crucial role in integrating audiovisual speech information and preventing illusory perceptions.
• Motor network engagement is topographically and temporally specific, contributing to accurate speech perception by mitigating multisensory illusions.