Acoustic and Perceptual Analyses of Expressive Prosody in Children with High-Functioning Autism: A Comparison of Speech From a Structured Task and Conversation

Background: Children with high-functioning autism (HFA) have communicative difficulties despite age-appropriate cognitive and languge abilities. Over time aspects of communication improve but difficulties with expressive prosody often persist, and these lead to negative perceptions on the part of listeners (Paul et al., 2005). Prosody, the melody of a person's voice, is conveyed through features such as pitch and speech rate. The literature reports varied and sometimes contradictory terms to describe prosodic abnormalities in HFA, such as monotonous or exaggerated intonation and a fast or slow speech rate.

Objectives: The aim of the study was to explore whether consistent acoustic markers of atypical prosody could be identified in school-age children with HFA, which could then be used to specify assessment and intervention plans. To this end speech samples were analyzed from two different settings: a structured communication task and unstructured conversation. In addition, perceptual ratings were collected on the conversation  samples to investigate how listener judgments relate to acoustic differences.

Methods: Participants were 8- to 14-year-olds with HFA or typical development (TYP), matched on language level, age and gender. In Study 1 speech samples were collected from15 HFA and 11 TYP children via a structured communication task where they produced instructions for a listener (e.g. "Pick up the cup"). Recorded audio was analyzed using PRAAT software (Boersma & Weenink, 2008). Each participant’s average pitch, pitch range, and speech rate were calculated. Study 2 examined the same three prosodic features in speech collected during an unstructured conversation with an adult. Conversation samples were collected from 15 HFA and 13 TYP children and an uninterrupted 10 to 13 second clip of each  participant’s speech was analyzed. In Study 3 thirty-two Speech-Language Pathology students, blind to group membership, rated the conversation speech samples according to a perceptual rating scale.

Results: Structured communication: HFA group had a higher mean pitch than the TYP group after controlling for age. There were no significant group differences in pitch range or speech rate. Conversation: acoustic analyses revealed significantly higher pitch range and a trend for higher average pitch in HFA group compared with the TYP group. Both groups produced a similar speech rate. These results are consistent with findings from narrative tasks, where children with HFA were reported to have increased pitch and/or pitch range (Diehl et al., 2007; Edelson et al., 2007). Perceptual ratings of conversational speech: blind raters reliably differentiated the HFA and TYP groups on the basis of “overall impression”of prosody, giving the HFA group more atypical scores. However, no individual prosodic feature reliably differentiated between groups. Moreover a multiple regression analysis revealed that acoustic differences did not significantly predict ratings of overall impression of normal/atypical prosody.

Conclusions: Acoustic analyses of speech in school-age children with HFA reveal higher mean pitch in structured communication and increased pitch range/sing-songy speech during conversation, rather than the stereotype of monotone intonation.