Representational Gestures Provide a Direct Link between Motor Behavior and Social Communication Deficits in ASD
Atypical motor behavior is widespread in ASD; individuals with ASD often display impairments in coordination, postural control, imitation, and praxis/pantomime performance. Praxis is the ability to perform learned skilled movements, and praxis weaknesses in ASD are associated with social-communication deficits (Dowell, Mahone, and Mostofsky, 2009). To date, research has only indirectly established a relationship between praxis performance and nonverbal communication, e.g., by correlating praxis and ADOS scores (Dziuk et al., 2007), leaving the question of mechanisms open. Here we propose a direct link between impoverished praxis skill and social-communication skills, via the performance of spontaneously produced co-speech hand gestures. Specifically, we predicted that participants with worse praxis scores would be less likely to use representational gestures (“descriptives” on the ADOS), in which speakers represent visuospatial information, such as shape or movement, with their hands.
To test the hypothesis that impoverished praxis skill is associated with decreased spontaneous production of representational gestures.
Verbally fluent adults with ASD (n=12) and typically developing controls (TDC; n=21) were group-matched on age, gender, and full-scale IQ (see Table). Praxis was assessed using an abbreviated version of the Florida Apraxia Battery, consisting of 19 items, including gesture to command, gesture to imitation, and gesture with tool use, which were coded for a range of errors. To assess spontaneous production of co-speech gestures, participants completed a five-trial referential communication task, in which they described abstract three-dimensional figures to a trained confederate. The task was designed to allow for back-and-forth conversational interaction in a controlled setting. All hand gestures produced during the task were coded for: (1) frequency (gestures per minute), (2) type (representational, interactive, deictic, beat, or other; see Table), and (3) confidence (rater’s confidence in the gesture’s meaning).
Participants with ASD made marginally more errors on the praxis task compared to controls, with a robust effect size (p=.063, d=.893). On the referential communication task, participants with ASD and TDC gestured at a similar overall rate (p=.151; d=.529), but participants with ASD were less likely to use representational gestures specifically (p=.007, d=1.67), and coders were marginally less confident about what their gestures meant (p=.07, d=1.12). Looking at gestures broadly, praxis error rate and co-speech gesture rate were not correlated (r=-.029, p=.874). However, participants who produced more praxis errors were less likely to select representational gestures specifically (r=-.649, p=<.001), a finding that held in the ASD group alone (r=-.642, p=.045), but not in the TDC group (r=-.279, p=.247, see Figure). Participants who made more praxis errors also produced gestures with lower confidence ratings (r=-.477, p=.009).
Adults with ASD who show greater deficits on a structured praxis exam are less likely to spontaneously produce representational gestures during conversation. Like praxis, representational gestures depend on access to underlying internal actions models, thus individuals with impoverished mental representations may evidence difficulty drawing on these representations both to perform skilled movements (i.e., praxis), and to perform communicative co-speech gestures. These findings demonstrate preliminary support for a direct link between motor skills impairments and communication skills in ASD.
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