Abstract/Summary

How pitch is processed has been investigated across different auditory domains (speech vs. music), processing levels (low-level vs. high-level), and modalities (perception vs. production) in individuals with autism spectrum disorder (ASD). However, mixed results have been reported with no substantial evidence to inform the ongoing theoretical debates in ASD, such as (a) whether speech and music processing share underlying mechanisms; (b) whether perception correlates with production; and (c) whether high-level information processing is intact in individuals with ASD. The present thesis reports three studies that examine pitch processing in individuals with and without ASD to inform the three aforementioned theoretical debates and to reconcile inconsistencies across studies. In relation to pitch processing in speech versus music, the results show that pitch perception in both domains is intact in individuals with ASD. However, when imitating speech and song, individuals with ASD demonstrate impaired absolute but not relative pitch production. These findings from perception and production suggest that speech and music pitch processing, whether intact or impaired, likely share underlying mechanisms. With respect to the relationship between perception and production, the findings indicate an association between these two modalities, since the ability to identify statement-question intonation is associated with the ability to imitate the intonation in both groups. Concerning low- and high-level processing, the findings reveal that high-level processing is not impaired in ASD, and that sensitivity to low-level pitch predicts performance on higher-level processing in both groups. Furthermore, perception ability increases with age in individuals with and without ASD whereas imitation ability does not. The findings from this thesis heighten our understanding of how pitch is decoded and encoded in ASD, and provide theoretical implications for pitch processing in this population and in typical development.