Looking to and Processing of Audiovisual Speech and Links with Language in Autism: Effects from Infancy Through Adolescence

Abstract

This dissertation encompassed a comprehensive characterization of audiovisual speech processing and its potential influence on language development in autism. First, we reviewed differences in audiovisual speech processing and perception in autism and potential influences on language development. In Chapter 2, we evaluated the stability of variables of audiovisual speech processing and perception derived from measures commonly used in the literature in autistic school-age children. We then focused on one of these variables – the P2 amplitude of the event-related potential (ERP) as measured by EEG in response to audiovisual versus auditory-only speech – to evaluate whether neural processing of audiovisual speech differs in autistic versus non-autistic school-age children, and whether individual differences in P2 amplitude responses covary with vocabulary. Finally, in Chapter 4, we extended our ERP findings to earlier in life, investigating whether ERP amplitudes in response to audiovisual versus auditory-only speech are present in 12-18-month-old infants, differ between infant siblings of autistic and non-autistic children, and covary with looking to audiovisual speech and emerging language ability. Through these approaches, we identified looking to audiovisual speech as measured by eye tracking and P2 amplitudes as measured by EEG as highly stable in autistic children. Additionally, we found ERP amplitude differences in response to audiovisual compared to auditory-only speech across infants and school-age children, but we did not find evidence of group differences in these ERP amplitude effects between autistic and non-autistic children or infant siblings of autistic children and infant siblings of non-autistic children. However, we found substantial individual variability in the magnitude of ERP amplitude differences in response to audiovisual versus auditory-only speech that covary with both looking to audiovisual speech and language ability. Importantly, we identified several participant characteristics that may influence these associations. Altogether, these findings provide ideas for mechanisms of the cascading effects of audiovisual integration onto language that may provide clinical utility for maximizing language outcomes for autistic individuals.