Simple Auditory Abilities And Effects Of Acoustic Phonetic Variability On Perceptual Processing In Autism

A number of perceptual-cognitive theories attempt to explain the autism phenotype. Some of these theories suggest auditory-perceptual differences in individuals with Autism Spectrum Disorders (ASD) occur at early processing stages, while others posit differences at later stages (e.g., speech perception), or combine both positions. For example, the Neural Complexity Hypothesis (Samson, Mottron, Jemel, Belin & Ciocca, 2006), states that individuals with ASD have superior low-level processing and inferior late stage processing compared to neurotypicals (NT). This claim is unsupported because previous behavioral studies of auditory perception in autism do not typically assess the same participants on simple and complex auditory processing tasks; further, when simple and complex stimuli are used in a single experiment, the response rarely focuses on the phonemic content of the stimulus. In the present investigation, participants with ASD and NTs were assessed on discrimination of pure tones and recognition of spoken words under varying conditions of complexity. The aim of these assessments was to determine if people with ASD had superior or diminished perceptual abilities compared to NTs. Performance of people with ASD was also compared to other aspects of development. Given the heterogeneity of the autism spectrum, such as variable presentation in symptom severity and common comorbid psychiatric conditions (Masi, DeMayo, Glozier & Guastella, 2017), we analyzed results at the level of groups, subgroups and individual performers. Consistent with previous findings, the ASD group had better frequency discrimination thresholds and intact duration discrimination. The ASD group's relatively superior performance on pitch discrimination was reversed when the perceptual task switched from basic auditory perception to speech recognition and as talker and rate normalization demands increased, resulting in greater differences between low- and high- level tasks. These results approximate but do not confirm the aforementioned perceptual-cognitive theories. Absolute support for these theories is limited because a) superior low-level perceptual processing was restricted to the frequency domain at the group level and b) while there was significantly poorer performance in the ASD group relative to NTs on higher-level tasks, examination of individual differences revealed that people within the ASD group showed a wide range of individual differences. Additional subgroup analyses indicated that perceptual differences in the current study were closely tied to parent-reported ADHD symptoms. Finally, there was some support for associations between speech and nonspeech processing in subsets of people with ASD.