Atypical multisensory integration in Autism Spectrum Disorders: Cascading impacts of altered temporal processing

A strong factor influencing multisensory integration is the temporal relationship between the sensory inputs that are combined. Individuals with Autism Spectrum Disorders (ASD) exhibit both atypical multisensory and temporal processing deficits relative to their typically developing (TD) peers. A series of behavioral and fMRI studies from our lab have focused on the link between these two processes. Using speech and non-speech stimuli with parametrically varied temporal relationships between the auditory and visual components, we showed that multisensory temporal processing is indeed altered in ASD, with the largest deficits observed with speech stimuli. The temporal changes seen with simple, non-speech stimuli are strongly correlated with behavioral measures of perceptual binding of audiovisual speech, which suggests that low-level multisensory temporal deficits have cascading effects on speech perception. To explore the neural substrates of these behavioral effects, we implemented an fMRI paradigm in individuals with ASD and TD where we presented synchronous and asynchronous speech and non-speech stimuli. We functionally localized a region in the superior temporal sulcus (pSTS), based on its involvement in multisensory binding and temporal processing and known functional and anatomical differences in ASD. Responses to audiovisual stimuli were extracted and compared across stimulus types and groups. Both TD and ASD groups show reduced pSTS activation with synchronous relative to asynchronous non-speech presentations, reflecting increased processing efficiency. For speech stimuli, only the TD group showed this effect. These data suggest differences in neural processing in pSTS may be at the core of atypical speech perception observed in ASD.