Prosody in Adolescents with Autism: The Impact of Language, Speech Motor Control, and Auditory Processing

Background: Some individuals with Autism Spectrum Disorder (ASD) exhibit differences in expressive and receptive prosody. There is lack of agreement regarding the characteristics and underlying processes associated with atypical prosody in this population. Current theories to explain atypical prosody in ASD range from poor language ability to speech motor control and/or auditory processing differences.

Objectives: We investigated the following research questions: 1) Do individuals with ASD perform less accurately than controls on expressive/receptive prosody tasks?; 2) Do individuals with ASD show significant differences on speech motor control tasks as compared to controls?; 3) Do individuals with ASD perform significantly different on auditory processing tasks compared to controls?

Methods: A between-group study was conducted to investigate prosody, language, speech motor control, and auditory processing among teenagers with ASD (n=11; ages 13;11 to 19;11 years) compared to TD controls (n=11) matched for age, gender, and receptive language (English). Participants completed: 1) standardized expressive and receptive vocabulary testing; 2) Profiling Elements of Prosody in Speech-Communication 2015 (PEPS-C 2015) to assess expressive/receptive prosody in pragmatic, affective, and grammatical domains; 3) Alternate Motion Rates (AMRs) to measure speed and precision of articulation, 4) Sequential Motor Rates to assess sequencing and coordination of the speech mechanism for articulation; and 5) the SCAN-3:A to screen auditory processing abilities. Trained listeners blind to participant group membership rated expressive prosody and motor speech tasks. Inter-rater reliability was good/moderate (Cohen’s kappa >.55; Altman, 1991).

Results: There were no significant differences between groups on standardized expressive (p=.189) or receptive (p=.054) vocabulary. The group with ASD performed significantly less accurate (p<.05) than the TD group on 12 out of 14 PEPS-C 2015 tasks. Regarding speech motor control, the participants with ASD performed with significantly a lower (p<.05) group mean (slower speech rate) for repetition of [p^] and [k^] syllables. No significant differences between groups were observed on motor programming/planning (SMRs). Trained listeners rated participants with ASD as sounding qualitatively different or “atypical” than controls on motor speech tasks. No significant differences were observed in auditory processing abilities (p=.635). Qualitative analyses revealed that among the group with ASD, 82% “failed” the PEPS-C 2015 expressive/receptive composite scores. Among these individuals, 27% had moderately to extremely low language; 73% qualitative differences in motor programming/planning and motor execution (e.g., 25% sequencing errors; 50% imprecise or slurred speech, respectively); and 22% failed the SCAN-3:A. Two (18%) with ASD who “passed” the PEPS-C, had moderately to extremely high language abilities; 9% failed the SCAN-3:A; and 9% exhibited minor sound substitutions and variable speech rate. All TD participants passed the PEPS-C 2015, had average to extremely high language, no qualitative differences on motor speech tasks; and 18% failed the SCAN-3:A.

Conclusions: This research supports that some individuals with ASD have atypical prosody. The underlying mechanisms of atypical prosody in this population cannot be attributed to only one mechanism since motor speech, language and auditory processing abilities are intertwined. There is evidence to support poorer motor speech abilities compared to language performance and vice versa in some individuals with ASD.