Interpersonal motor interactions (joint-action) occur on a daily basis. For example, when a friend passes you a cup of coffee, grasping the cup requires different preparation for each individual. In situations such as this, typically developing individuals plan their grip orientation to finish in a comfortable posture, even if it means adopting an uncomfortable posture earlier in the action sequence (i.e., end-state comfort; Rosenbaum, 1992). In joint-action situations typically developing individuals consider the end-goal of their partner and adjust their own movements to accommodate the other person (Gonzalez et al. 2011). The movement planning processes required for interpersonal motor interactions may be difficult for individuals with an Autism Spectrum Disorder (ASD) given the documented differences in performance on theory of mind and imitation tasks.
The goal of the present experiment was to determine if individuals with ASD exhibit end-state comfort behaviours similar to their typically developing peers in joint-action situations. Specifically, do individuals with ASD anticipate how another person will use an object and pass the object in a manner that facilitates the end-goal of the recipient?
We replicated the tasks performed by Gonzalez et al. (2011) with a group of young adults with ASD (N=10; M=32.7 years). Participants were asked to either pass, place, or use three common tools: a wooden toy hammer, a stick, or a calculator. These tools were selected because the degree of affordance they offer (i.e., the physical characteristics they posses to prompt proper use) ranges from direct (hammer) to indirect (calculator). Participants were asked to pass the tool to a confederate who was either going to place the tool down, or use the tool for its intended task. Variables of interest included beginning and end-state grip orientations of both the participant and confederate (i.e., comfortable or uncomfortable) as a function of task goal, and the side to which the tool was placed or passed to (i.e., ipsilateral or contralateral).
Similar to Gonzalez et al. (2011), where typically developing young adults maximized their partner’s end-state comfort by adopting personally uncomfortable passing postures, individuals with ASD also passed tools in a manner that facilitated comfortable end-use by the confederate. However, individuals with ASD performed with greater variability compared to their typically developing peers. Individuals with ASD were most consistent using the stick or hammer, and most variable when using the calculator.
The results of the present study provide evidence that the movement planning processes participants use to prepare to pass a tool are not stereotypical for individuals with ASD. We propose that performance on the interpersonal motor interactions reported here represent an important link between motor performance and more complex imitation or communication tasks.
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