Cross-modal Suppression of Auditory Association Cortex by Visual Speech as a Mechanism for Audiovisual Speech Perception

Vision provides a perceptual head start for speech perception because most speech is “mouth-leading”: visual information from the talker’s mouth is available before auditory information from the voice. However, some speech is “voice-leading” (auditory before visual). Consistent with a model in which vision modulates subsequent auditory processing, there was a larger perceptual benefit of visual speech for mouth-leading vs. voice-leading words (28% vs. 4%). The neural substrates of this difference were examined by recording broadband high-frequency activity from electrodes implanted over auditory association cortex in the posterior superior temporal gyrus (pSTG) of epileptic patients. Responses were smaller for audiovisual vs. auditory-only mouth-leading words (34% difference) while there was little difference (5%) for voice-leading words. Evidence for cross-modal suppression of auditory cortex complements our previous work showing enhancement of visual cortex (Ozker et al., 2018b) and confirms that multisensory interactions are a powerful modulator of activity throughout the speech perception network. Impact Statement Human perception and brain responses differ between words in which mouth movements are visible before the voice is heard and words for which the reverse is true.