Large Scale Functional Brain Networks Underlying Temporal Integration of Audio-Visual Speech Perception: An EEG Study

Area of Science:

• Neuroscience
• Auditory Perception
• Multisensory Integration

Background:

• Observable lip movements significantly influence auditory speech perception, exemplified by the McGurk effect with incongruent audio-visual (AV) stimuli.
• Previous neuroimaging studies highlight frontal, parietal, and superior temporal sulcus (STS) regions in multisensory speech perception.
• The role of large-scale brain networks in processing and fusing AV speech remains an open question.

Purpose of the Study:

• To investigate the characteristics of the large-scale cortical network facilitating multisensory speech perception.
• To explore functional connectivity dynamics during synchronous and asynchronous AV speech perception using electroencephalogram (EEG).
• To understand the temporal integration mechanisms underlying multisensory speech perception within a whole-brain framework.

Main Methods:

• Utilized electroencephalogram (EEG) recordings and exploited trial-by-trial perceptual variability of incongruent AV speech stimuli.
• Analyzed the spectral landscape of EEG signals at varying AV lags (temporal differences between audio and visual stimuli).
• Computed functional connectivity dynamics using time-frequency global coherence to assess pairwise coherence changes over time.

Main Results:

• During synchronous AV speech, enhanced global gamma-band coherence and decreased alpha and beta-band coherence were observed for cross-modal (illusory) perception (300-600 ms post-stimulus onset).
• For asynchronous speech stimuli, global broadband coherence occurred earlier during cross-modal perception.
• Pre-stimulus decreases in lower frequency power (alpha for positive AV lags, theta for negative AV lags) were noted during asynchronous conditions.

Conclusions:

• Multisensory speech perception relies on large-scale functional brain network mechanisms, extending beyond established cortical loci.
• Temporal integration of AV speech involves dynamic changes in neural coherence across different frequency bands.
• Understanding multisensory speech perception necessitates a framework that incorporates whole-brain functional connectivity dynamics.