Characterization of central auditory processing in minimally and low verbal adolescents with autism
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Autism spectrum disorder (ASD) is a neurodevelopmental disorder in which individuals demonstrate deficits in social communication and repetitive or restricted behaviors or interests. About one-third never attain fluent expressive language and remain minimally or low verbal (ASD-MLV). We hypothesized that central auditory processing is particularly disrupted in ASD-MLV given the shared neural substrates of sound processing and language. To address this hypothesis, we conducted four empirical studies designed to capture neural and behavioral correlates of central auditory processing in children and adolescents who were either typically developing (TD), verbally fluent with ASD (ASD-V), or ASD-MLV. Our first study established that adult-like neural indices of sound organization as measured by mismatch responses (MMRs) during a passive stream segregation task were not observable until adolescence in TD participants, ages 3 to 21 (N=65). Findings led us to focus subsequent studies on adolescents. In our second study, we conducted a meta-analysis of experiments that had compared MMRs between TD and ASD samples (N=721). We identified that while there was some evidence suggesting that perceptual sound organization (as evidenced by MMR) was more dysfunctional in those with ASD, more research was needed to validate this pattern in adolescents and low verbal samples. In our third study (N=83), we determined that atypical auditory behaviors occurred most often in those with ASD with combined expressive and receptive language impairments; furthermore, the percentage of time exhibiting such behaviors was associated with weaker MMRs. In our final study (N=74), we quantified neural orienting responses to one’s own name in a multispeaker setting – a task that requires higher-order stream segregation and social auditory attention – in adolescents. We found that responses were weaker in ASD-MLV compared to ASD-V and TD participants. In addition, strength of response in those with ASD was negatively correlated with parent-reported signs of auditory-specific attentional deficits, as measured by the Short Sensory Profile Auditory Filtering Subscale. With this dissertation, we found atypical neural indices of auditory processing in ASD-MLV adolescents and discuss theoretical implications for why central auditory processing might be particularly pronounced in the ASD-MLV phenotype.