Human perception is often shaped by simultaneous multimodal stimuli; however, the neural mechanisms governing cross-modal interactions in perceptual formation remain unclear.
We investigate the functional connectivity and large-scale cortical network dynamics involved in audiovisual integration during bistable auditory perception. Using paired tones with bistable percepts combined with visual flickering, we analyzed human brain activity during both synchronous and desynchronized conditions. Participants reported their dominant percept as well as their judgments of simultaneity. The behavioral results indicated a significantly higher two-stream perception rate in the synchronized condition compared to the desynchronized condition, suggesting that the integration of audio and visual stimuli enhances two-stream perception. Following the recording of electroencephalography (EEG), raw data were preprocessed using a bandpass filter and independent component analysis for artifact removal. EEG analysis revealed higher alpha and delta power activity in frontal regions, along with elevated alpha in occipital areas during synchronous conditions. Phase-amplitude coupling (PAC) between frontal delta-phase and occipital alpha-amplitude was significantly stronger in the synchronous condition, indicating that fronto-occipital PAC is a key mechanism in audiovisual integration. Moreover, microstate analysis revealed distinct spatiotemporal dynamics: in the asynchronous condition, frontal alpha power correlated with the duration and transitions of microstate class D, indicating top-down cognitive control. Conversely, in synchronous conditions, occipital delta power correlated with the dynamics of the same microstate class, suggesting bottom-up sensory integration.These results highlight that audiovisual perception involves both local oscillatory interactions and global network dynamics (fronto-occipital PAC), where synchronous stimuli enhance bottom-up integration, while asynchronous processing relies more on top-down modulation.
Overall, these results reflect the neural mechanisms through which cross-modal stimuli influence perception via coordinated local and large-scale brain network activity.