Motor Behavior As a Qualitative Difference in the Spontaneous Production of Co-Speech Hand Gestures By Adults with Autism Spectrum Disorders
Deficits in nonverbal communication are a required symptom for diagnosis of autism spectrum disorder (ASD). DSM-5 stresses that nonverbal communication in ASD is often characterized by qualitative differences, in addition to reduced frequency. These qualitative differences have been inadequately described, in part because qualitative features of behavior are by definition challenging to quantify. Here we examine one qualitative feature of nonverbal communication in ASD: motor behavior during spontaneously produced co-speech hand gestures.
The literature on co-speech gesture in ASD is limited, but suggests that qualitative differences, e.g., in how gesture is formed, used functionally, or integrated with speech, best discriminate ASD from typically developing controls (TDC). Atypical motor behavior is widespread in ASD, both across individuals and across possible motor acts. Reported differences in motor behavior in ASD include low muscle tone, atypical gait, and impairments in praxis/pantomime performance. In typical adults, motor features of gesture (e.g., frequency and size of movements) are associated with empathy, suggesting a relationship between motor behavior during communication and broader social-cognitive deficits associated with ASD.
The primary objective of this study was to determine whether differences in motor features, including movement frequency, size, and complexity, would be observed in co-speech gestures spontaneously produced by adults with ASD.
Adults with ASD (n=24) and typically developing controls (n=10) were matched on chronological age, gender, and full scale IQ (all average or above). Data on 14 additional TDCs will be available and analyzed by May 2017. Participants completed a five-trial referential communication task, employed through two networked laptops, in which they described abstract three-dimensional monochromatic 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 tagged and coded for: (1) movement frequency (gestures per minute), (2) movement size (degree to which hand moved through space), and (3) movement complexity(single-handed vs. two-handed gestures).
Both groups performed very well on the task (96% accuracy across trials in both groups), and all participants in the study gestured at least twice during the 20-minute task (Range: 2-176 total gestures). Overall, participants with ASD produced less movement than those with TDC (p=.04, Cohens d=0.97; Figure 1), evidenced by marginally less frequent gestures (p=.11; Cohen’s d=0.72) and significantly smaller movements (p=.005, Cohen’s d=0.91) in ASD. There was a significant interaction between hand usage and group with a large effect size (p=.002, Cohen’s d=1.23; Figure 2), with participants with ASD using more single-handed gestures and TDC participants using more two-handed gestures.
During spontaneous interaction, adults with ASD produced fewer, smaller, and less complex co-speech gestures. Motor features of co-speech gesture as a qualitative difference in nonverbal communication in ASD vs. TDCs can be quantified. All features described here can be measured by existing technologies, with potential to increase both the precision and scale of measurement, allowing for larger samples, and possible use as a behavioral biomarker of ASD.
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