Kinematic and force control features in autistic adults during curvilinear movements

Lu, Szu-Ching and Rowe, Philip and Pollick, Frank and Delafield-Butt, Jonathan (2023) Kinematic and force control features in autistic adults during curvilinear movements. In: International Society for Autism Research (INSAR) 2023 Annual Meeting, 2023-05-03 - 2023-05-06, Stockholmsmässan.

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Abstract

Background: Motor challenges have been reported in 87% of autistic children (Bhat, 2020) and may persist into adulthood (Cho et al., 2022), which could underpin autistic social difficulties. Kinematic differences between individuals with autism spectrum disorders (ASD) and typical development (TD) have been reported across activities. The two-thirds power law (2/3 PL) defines the relationship between moving speed and the curvature of moving path. Different adherence to 2/3 PL was observed in autistic children (Fourie et al., 2022), but not yet tested in autistic adults. Additionally, force modulation is affected in autistic individuals (Shafer et al., 2021). Force quantification during the 2/3 PL task can help further understand autistic motor regulation during the task. This contributes to the computational characterisation of ‘autism motor signature’ (Anzulewicz et al., 2016), leading to a better understanding of motor challenges and required support in autism. Objectives: Quantify the kinematic and force control features in autistic adults during curvilinear movements, and to test if these differ from their TD counterparts. Methods: Nine autistic and twelve typically developing adults (age ranged 19-57 years) participated in this study. Participants used a stylus (Apple Pencil) to trace and draw ellipses on a smart tablet (iPad Pro 11-inch) while timestamped on-screen trajectory and force data were recorded. An elliptical path was shown on screen for tracing while an empty canvas was provided for drawing ellipses (Figure 1). Each participant performed 5 trials of tracing and then 5 trials of drawing activities. Each trial lasted around 15 seconds. The longest continuous movement was extracted from each trial for further analyses. The radius of curvature and tangential velocity were computed to give the β value (Tangential Velocity = K * Radius of Curvature β) representing adherence to 2/3 PL. Force data were first normalised by the maximum value of the trial and then averaged, indicating the average ratio of force applied with respect to the maximum force. Kolmogorov-Smirnov test was used to compare the distributions of kinematic and force variables between ASD and TD movements. Results: In comparison to typically developing adults, autistic adults demonstrated greater deviation from the 2/3 PL (β=.333) in both tracing (ASD Mdn=.302, TD Mdn=.323, p=.010) and drawing (ASD Mdn=.306, TD Mdn=.323, p=.002) activities (Figure 2a). In addition, autistic adults applied greater normalised force in both tracing (ASD Mdn=.501, TD Mdn=.452, p=.038) and drawing (ASD Mdn=.498, TD Mdn=.453, p=.032) activities than their typically developing counterparts (Figure 2b). Conclusions: This study revealed the kinematic and force control differences in autistic adults during ellipse tracing and drawing activities. These differences could lead to an impact on their quality of life as curvilinear movements are essential in daily life activities such as writing, ball throwing, and turning a car wheel. Understanding motor control differences may help develop intervention plans to overcome motor challenges and hence improve life quality. Furthermore, these motor control differences may be related to their brainstem function (Delafield-Butt & Trevarthen, 2018). This research paradigm could support future investigations on the relation between motor features and brain function.

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