25692
Vocalizations of Minimally Verbal Children and Adolescents with Autism: A Prosodic and Acoustic Analysis
Variations in prosody convey lexical, grammatical, and pragmatic meaning, all essential for successful communication. Individuals with autism spectrum disorder (ASD) show deficits in communication and pragmatic use of language (Tager-Flusberg Paul & Lord, 2005), with mixed results for how stress, intonation, and phrasing distinctions are employed (Paul et al., 2005; McCann et al., 2007; Shriberg et al., 2001). Critically, research to date has largely focused on verbal individuals with ASD, and only a few studies include acoustic analyses to more closely examine the nature of expressive impairments (Baltaxe, 1984; Diehl et al., 2009).
Objectives:
The current investigation was designed to elucidate the prosodic abilities of minimally verbal school-aged children with ASD, a previously understudied population, in an effort to better understand communication abilities across the spectrum. Due to challenges in collecting data from a population with a range of behavioral and intellectual issues, research has been limited within this group. Our goal was to acoustically analyze different types of vocalizations to better identify and understand natural prosodic features.
Methods:
Speech from 24 minimally verbal children and adolescents was analyzed (see Table 1). All speech was extracted from a standardized interview (ADOS) and labeled as spontaneous, echolalia, or elicited imitation. Average F0 was extracted from successive 250-ms time windows, resulting in four data points per second. Average pitch is the average of these data points, and pitch range is the standard deviation in average F0. Due to the heterogeneity of this population, we predicted that participants would demonstrate differences in prosody through the varied use of F0, with pitch fluctuating as a result of verbal ability. This is in contrast to typically developing populations where variability stabilizes over time. Verbal ability was measured by analyzing how many unique words were uttered during the assessment (Lexical Score), allowing for a more fine-grained verbal analysis.
Results:
Substantial prosodic variation was observed across participants. Strong correlations were found between Lexical Score and the child’s score on a parental questionnaire of receptive and expressive vocabulary (r(21) = .758, p < .001; r(21) = .786, p < .001, respectively). Lexical Score negatively correlated with average pitch, with more verbal children demonstrating lower overall pitch (r(20) = -.563, p = .006). Pitch range varied more within spontaneous productions than the echolalia and elicited imitations, the latter two showing overall greater variation in range (Figure 1). In comparison to previous research with verbal children with ASD and typically developing children, our data show more pitch range variation for minimally verbal children (Diehl et al., 2009).
Conclusions:
Results indicate that participants vary considerably in how they modulate pitch during different types of speech productions. This first exploration into the prosodic patterns of pitch in minimally verbal school-aged children with ASD provides further insight into how prosody varies along the autism spectrum. We also investigated how pitch varies for this group as a function of speech type, shedding light on unique processing and production strategies. Identifying prosodic characteristics aids early intervention strategies and provides a baseline for melodic-based therapies.