Auditory stimuli extend the temporal window of visual integration by modulating alpha-band oscillations

In multisensory environments, signals from different modalities interact to shape perception, but the underlying temporal dynamics remain unclear. We investigated how a brief auditory stimulus affects the temporal integration of successive visual events using electroencephalography (EEG). Participants viewed two consecutive flashes, with or without an auditory beep accompanying the first flash, and reported whether they perceived one or two flashes. The beep shifted the psychometric fusion threshold to longer interstimulus intervals, indicating a wider temporal integration window. This behavioural shift was accompanied by a transient reduction in poststimulus instantaneous alpha frequency, and individual differences in alpha-cycle lengthening correlated with threshold prolongation. Auditory input also weakened the relationship between prestimulus alpha frequency and perceptual report while strengthening the corresponding relationship with prestimulus alpha phase. In a follow-up transcranial alternating current stimulation (tACS) experiment, the effects of lower- versus upper-alpha stimulation on fusion thresholds differed between the visual-only and audiovisual conditions. A computational model based on phase resetting and perceptual cycles qualitatively reproduced the main findings. Together, the results suggest that a brief sound can reorganize alpha-band timing and thereby widen the temporal window of visual integration.