Deliberate synchronization of speech and gesture: Effects of neurodiversity and development.

The production of speech and gesture is exquisitely temporally coordinated. In autistic individuals, speech-gesture synchrony during spontaneous discourse is disrupted. To evaluate whether this asynchrony reflects motor coordination versus language production processes, the current study examined performed hand movements during speech in youth with autism spectrum disorder (ASD) compared to neurotypical youth. Neurotypical adult performance provided a mature baseline. Participants read aloud rhythmic nursery rhymes, while producing a beat-like hand movement. An automated pixel-change video measure identified kinematic peaks; using smoothed acoustic envelope analyses, we identified peaks in speech. Results indicated few diagnostic group differences in explicit speech-movement coordination, although adolescent performance differed from adults. Adults demonstrated higher tempo and greater rhythmicity in their coordination; this group difference suggests that the method is sufficiently subtle to reveal individual differences and that this form of complex coordination undergoes ongoing maturation beyond adolescence. The sample is small, and thus results are necessarily preliminary. In the context of prior speech-gesture coordination studies, these findings of intact synchrony are consistent with the hypothesis that it is the demands of discourse planning, rather than motor coordination, that have led to prior findings of asynchony during spontaneous speech; this possibility awaits future research.