Acoustic Differences in the Imitation of Prosodic Patterns by Children with Autism Spectrum Disorders

Background: Atypical prosody production is a characteristic feature of autism spectrum disorders (ASD), regardless of the child's level of functioning.  To date, however, many of the studies of prosody performance have not captured the full extent of the deficits that are observed clinically. Although behavioral studies have given us some insight into the nature of differences between children with ASD and other children, acoustic measures of speech are often more sensitive to more subtle differences between populations. Moreover, most studies just focus on the functional use of prosody (e.g., to communicate affect, intent in discourse, syntactic structure). It is possible that deficits in basic abilities, such as imitation, could offer some insight into patterns of prosody performance in ASD.

Objectives: Our objective is to examine acoustic differences in prosodic patterns produced in imitated speech.  

Methods: Participants were 24 children and adolescents (ages 8-16) with ASD and average general language functioning, 22 typical controls (ages 8-17), and 16 children with language impairment (ages 9-17). All groups were matched on chronological age and gender. Participants were given two prosody imitation tasks from the Profiling Elements of Prosodic Systems in Children (PEPS-C), a norm-referenced measure of prosody perception and production for children. One task involved imitating prosodic patterns in single words, and the other task involved imitation across whole utterances. Speech data were also acoustically analyzed using PRAAT, a program for speech analysis and synthesis. Speech data were analyzed for the following acoustic measures:  average pitch, pitch range (maximum pitch minus minimum pitch), pitch variance, duration, and intensity.

Results: Participants with ASD exhibited a significantly longer duration of utterances when imitating single words than the typically developing controls, F(1,44)=6.47, p<.05, and children with language impairment F(1,38)=3.49, p<.05.  Participants with ASD also had longer utterance durations than the other groups for whole phrases, although these differences did not reach significance.  There were no other acoustical differences (pitch range, pitch variance, average pitch, intensity) between participants with ASD and typical controls. Children with language impairment showed significantly more pitch variance than participants with ASD and typical controls on both tasks. This finding, however, is likely qualified by the fact that the sample of children with language impairment had a higher average pitch overall (higher voice) than children with ASD, F(1,38)=3.23, p<.05, and typical controls F(1,36)=5.87, p<.05, because children with a higher voice also tend to have greater pitch variance.  

Conclusions:   This study found that children with ASD produce longer utterances than children with language impairment and typically developing controls when imitating speech. This suggests that fundamental deficits in the speech production system might contribute to some of the prosody production deficits seen in ASDs.