Adults with Autism Spectrum Disorder Demonstrate Increased Disfluency in Spontaneous Speech but Not in Reading

This study aimed to analyse the frequency and types of disfluencies in spontaneous speech and reading among adults with autism spectrum disorder (ASD) compared to neurotypical adults.

The participants were 56 Dutch-speaking adults, 28 with ASD and 28 age- and gender-matched controls. Samples of spontaneous speech and text reading were orthographically transcribed, and the speech disfluencies were identified and classified, using an expanded version of the Illinois Disfluency Classification System. The frequencies of stuttering-like disfluencies (SLDs), other disfluencies (ODs), word-final disfluencies (WFDs), and total disfluencies (TDs) were calculated.

Adults with ASD exhibited significantly more SLDs and WFDs in spontaneous speech than the control group. While no statistically significant differences were observed between both groups in reading, a trend towards increased WFDs was noted.

Adults with ASD exhibit increased speech disfluencies, more specific SLDs and WFDs, in spontaneous speech, than neurotypical adults, but not during reading. This discrepancy may arise because spontaneous speech requires real-time language formulation and social communication skills, which can differ in ASD, whereas reading offers an external linguistic structure that reduces cognitive and social processing demands. Increased speech disfluencies may impact how speech is perceived in terms of intelligibility and/or social communication dynamics.

What is already known on this subject Individuals with autism spectrum disorder (ASD) often exhibit challenges in pragmatic language use along with varying abilities in vocabulary, grammar and speech production. Concerning the latter, a limited body of research has identified specific characteristics of speech fluency in individuals with ASD, including a higher frequency of speech disfluencies and the occurrence of word-final disfluencies. What this study adds to the existing knowledge However, research on speech disfluency in people with ASD remains all in all limited. To date, only two studies have conducted an in-depth analysis of disfluency types using an elaborate classification system such as the Illinois Disfluency Classification System, both incorporating neurotypical control groups. One study focused on English-speaking school-aged children and the other on Finnish-speaking young adults. As these studies are confined to two linguistically distinct populations and based on similar speech sample types, the generalizability of their findings to other languages and speech samples remains uncertain. In the current study, we analysed the speech disfluency of Dutch-speaking adults with ASD, with a broader age range. In addition to the analysis of spontaneous speech, also a standard reading text was included to evaluate the impact of sample type. This study therefore extends the existing database and provides further insights into the types and frequency of speech disfluencies in adults with ASD. What are the potential or actual clinical implications for this work? Increased speech disfluencies can affect the speech intelligibility and/or social interaction of adults with ASD. Moreover, the integration of a more detailed analysis of disfluencies in individuals with ASD as part of a broader overall assessment might optimize the diagnostical and clinical decision-making process.