Children's Use of Disfluencies Distinguish ASD and Language Impairment

Background: Deficits in social communication, and pragmatic language in particular, are characteristic of individuals with autism spectrum disorders (ASD). The filled pause markers "uh" and "um" play a subtle role in shaping discourse; they are not merely speech errors. Filled pauses (FPs) provide valuable cues to the listener and are used to signal uncertainty, speech repairs, production difficulties, and to negotiate control of the floor. Typically developing children are thought to be sensitive to these cues and their meaning as early as age two. Children with ASD who are verbal are also known to use filled pauses conventionally, i.e., to signal production difficulties. "Um" is thought to play a larger role in shaping discourse, and its use to be under conscious control; "uh" is less salient, and its use is largely automatic. Given this, we hypothesized that communication impairments in children with ASD would selectively spare "uh" but produce lower rates of "um".

Objectives: This study compares the relative frequencies of "uh" and "um" in the spontaneous speech of children with ASD (with or without comorbid language impairment) to two control groups.

Methods: Participants: 112 children ages 3;10–9;0 participated: ASD (50), Specific Language Impairment (SLI;  18), and Typical Development (TD; 44). All diagnoses were verified by best-estimate clinical consensus. The children with ASD were split into two groups: one group with comorbid language impairment (ALI) as diagnosed by a CELF Core Language Score below 85, and one group with ASD but no clinical language impairment (ALN). All children were high functioning monolingual English speakers. Data collection: a clinician administered the Autism Diagnostic Observation Schedule (ADOS; module 2 or 3) to each child. Sessions were recorded and transcribed. Software was used to count each child's FPs; 4,067 FP tokens were collected in all. Group matching: All groups were matched on chronological age. The ALI/ALN group pair was also matched on ADOS severity score and Social Communication Questionnaire score. The ALN/TD and ALI/SLI group pairs were also matched on PIQ and VIQ.

Results: For all group pairs, diagnosis was uncorrelated with overall (i.e., "uh" + "um") rate of filled pause use. FP choice was analyzed for each comparison set using mixed effects logistic regression, with chronological age, FSIQ, ADOS "activity", and utterance position (utterance-initial vs. non-initial) as covariates. Diagnosis was a significant predictor for ALN/TD (p = .001) and ALI/SLI (p = .038); in both comparisons the ASD group used fewer instances of "um". Diagnosis was non-significant for TD/SLI (p = .888) and ALI/ALN (p = .814). ALI and ALN groups both used "uh" and "um" at an approximately 1:1 ratio, whereas TD and SLI groups used "um" 2 to 3 times more often than "uh". ADOS "activity" and utterance position were also significant predictors of FP choice; remaining covariates were non-significant.

Conclusions: The relative use of "uh" and "um" in spontaneous speech is highly sensitive to ASD diagnostic status, but insensitive to language impairment. This provides clinicians with a novel feature distinguishing ASD and SLI, a notoriously difficult differential diagnosis.