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Putative mechanisms mediating tolerance for audiovisual stimulus onset asynchrony
Jyoti Bhat1, Lee M Miller2, Mark A Pitt3
1Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, College of Medicine, Columbus, Ohio;
Journal of Neurophysiology
|December 16, 2014
Summary
Audiovisual speech perception tolerates timing differences by suppressing early auditory signals. This neural inhibition, alongside higher-level processing, broadens temporal integration windows for enhanced audiovisual synchrony perception.
Area of Science:
- Neuroscience
- Auditory Perception
- Speech Processing
Background:
- Audiovisual (AV) speech perception exhibits remarkable robustness to temporal discrepancies between visual and auditory stimuli.
- Understanding the neural basis of tolerance for audiovisual stimulus onset asynchrony (AVOA) is crucial for explaining this perceptual flexibility.
Purpose of the Study:
- To investigate the neural mechanisms underlying tolerance for audiovisual stimulus onset asynchrony (AVOA) using electroencephalography (EEG).
- To determine how the brain processes and integrates temporally mismatched auditory and visual speech information.
Main Methods:
- Participants judged the synchrony of AV words with varying onsets of voice and mouth movements.
- EEG recorded auditory evoked potentials (AEPs) and spectral power in alpha and beta bands.
- Analysis focused on neural responses time-locked to sound onsets and subsequent oscillatory activity.
Main Results:
- Behaviorally, longerAVOA tolerance was observed when visual mouth movements preceded auditory speech (V-A) compared to the reverse (A-V).
- Reduced P1-N1-P2 AEP amplitudes correlated with in-sync percepts, suggesting inhibition of low-level auditory processing.
- Increased beta and alpha band power during in-sync perception indicated involvement of higher-level neural processes.
Conclusions:
- AVOA tolerance is facilitated by inhibiting early auditory cortical activity, weakening the mapping of acoustic onsets.
- Higher-level neural processes, including those involved in attention and phonetic/lexical coding, contribute to wider temporal integration windows for AV speech.
- These mechanisms collectively enhance the brain's ability to integrate temporally disparate audiovisual speech information.
