Naturalistic Movie Viewing Reveals a Distributed Network Supporting Audiovisual Speech Processing

Traditional paradigms in cognitive neuroscience often fail to capture the richness of real-world experiences. To bridge this gap, researchers increasingly use naturalistic stimuli such as movies, which provide complex, multisensory input. Speech perception is a prime example of such complexity: it is inherently multisensory, involving the integration of auditory cues, lip movements, and facial expressions. Prior studies suggest that the left posterior superior temporal sulcus (pSTS) and superior temporal gyrus (STG) play a critical role in this integration. However, most studies of audiovisual speech have relied on simplified or artificial stimuli, limiting ecological validity. To address these gaps, we analyzed fMRI data from human participants watching two full-length films (500 Days of Summer, Citizenfour) to assess the consistency of multisensory speech processes across distinct genres and narratives. We manually annotated word onset times and modality (audiovisual vs. auditory-only). Across two movies and 38 participants we observed consistent speech-related activation in the pSTS and STG across speech types. Compared to auditory-only speech, audiovisual speech recruited a broad left-lateralized network including the angular gyrus, posterior temporal cortex, temporal pole, and inferior frontal gyrus, along with the right cerebellum. These findings were also consistently present in single-subject data. Importantly, most of the regions observed in our analyses have been implicated in multisensory function in the nonhuman primate literature despite receiving relatively little focus in human neuroimaging. Together our results demonstrate that speech processing during naturalistic viewing recruits a distributed network extending substantially beyond regions traditionally emphasized in audiovisual speech research.