Time course of multisensory interactions during audiovisual speech perception in humans: a magnetoencephalographic study.

During social interaction speech is perceived simultaneously by audition and vision. We studied interactions in the processing of auditory (A) and visual (V) speech signals in the human brain by comparing neuromagnetic responses to phonetically congruent audiovisual (AV) syllables with the arithmetic sum of responses to A and V syllables. Differences between AV and A+V responses were found bilaterally in the auditory cortices 150-200 ms and in the right superior temporal sulcus (STS) 250-600 ms after stimulus onset, showing that both sensory-specific and multisensory regions of the human temporal cortices are involved in AV speech processing. Importantly, our results suggest that AV interaction in the auditory cortex precedes that in the multisensory STS region.