The ability to understand spoken language is essential for social, vocational, and emotional health, but can be disrupted by environmental noise, injury, or hearing loss. These auditory deficits can be ameliorated by visual speech signals that convey redundant or supplemental speech information, but the brain regions critically responsible for these audiovisual (AV) interactions remain poorly understood. Previous TMS and lesion-mapping studies suggest that the left posterior superior temporal sulcus (pSTS) is causally implicated in producing the McGurk effect, an AV illusion in which auditory and visual speech are perceptually "fused." However, previous research suggests that the McGurk effect is neurally and behaviorally dissociable from other visual effects on speech perception and, therefore, may not provide a generalizable index of AV interactions in speech perception more broadly. To examine whether the left pSTS is critically responsible for AV speech integration more broadly, we measured the strength of the McGurk effect, AV facilitation effects, and AV conflict effects longitudinally over 2 years in patients undergoing surgery for intrinsic tumors in the left pSTS (n = 2) or frontal lobes (control; n = 14). Results demonstrated that left pSTS lesions impaired experience of the McGurk effect, but did not uniformly reduce visual influences on speech perception. Additionally, when multisensory behaviors were affected by a lesion, AV speech perception abilities could recover over time. Our results suggest a causal dissociation between perceptual benefits produced by congruent AV speech and perceptual modulations produced by incongruent AV speech (the McGurk effect). These data are consistent with models proposing that that the pSTS is only one of multiple critical areas necessary for AV speech interactions.
bioRxiv Subject Collection: Neuroscience