Visual stimulus locking of EEG is modulated by temporal congruency of auditory stimuli

Disparate sensory streams originating from a common underlying event share similar dynamics, and this plays an important part in multisensory integration. Here we investigate audiovisual binding by presenting continuously changing, temporally congruent and incongruent stimuli. Recorded EEG signals are used to quantify spectrotemporal and waveform locking of neural activity to stimulus dynamics. Spectrotemporal analysis reveals locking to visual stimulus dynamics in both a broad alpha and the beta band. The properties of these effects suggest they are a correlate of bottom-up processing in the visual system. Waveform locking reveals two cortically distinct processes that lock to visual stimulus dynamics with differing topographies and time lags relative to the stimuli. Most importantly, these are modulated in strength by the congruency of an accompanying auditory stream. In addition, the waveform locking found at occipital electrodes shows an increase over stimulus duration for visual and congruent audiovisual stimuli. Hence we argue that these effects reflect audiovisual interaction. We thus propose that spectrotemporal and waveform locking reflect different mechanisms involved in the processing of dynamic audiovisual stimuli.