Abstract
Reaching and grasping (prehension) is one of the earliest developing motor skills in humans, but continued prehension development in childhood and adolescence enables the performance of increasingly complex manual tasks. In individuals with autism spectrum disorder (ASD) atypical unimanual reaching and grasping has been reported, but to date, no studies have investigated discrete bimanual movements. We examined unimanual and bimanual reach to grasp tasks in youth with ASD to better understand how motor performance might change with increasing complexity. Twenty youth with ASD (10.1 ± 2.4 years) and 17 youth with typical development (TD) (9.6 ± 2.6 years) were instructed to reach and grasp cubes that became illuminated. Participants were asked to reach out with the right and/or left hands to grasp and lift targets located at near (18 cm) and/or far (28 cm) distances. For the unimanual (simplest) condition, participants grasped one illuminated cube (with either the left or right hand). For the bimanual conditions, participants grasped two illuminated cubes located at the same distance from the start position (bimanual symmetric condition) or two illuminated cubes located at different distances (bimanual asymmetric condition). Significant interactions among diagnostic group, task complexity, and age were found for initiation time (IT) and movement time (MT). Specifically, the older children in both groups initiated and performed their movements faster in the unimanual condition than in the bimanual conditions, although the older children with ASD produced slower ITs and MTs compared to typically developing peers across all three conditions. Surprisingly, the younger children with ASD had similar ITs and MTs as their peers for the unimanual condition but did not considerably slow these times to adjust for the complexity of the bimanual tasks. We hypothesize that they chose to re-use the motor plans that were generated for the unimanual trials rather than generate more appropriate motor plans for the bimanual tasks. An atypical spatiotemporal relationship between MT and peak aperture (PA) was also found in the ASD group. Together, our results suggest deficits in motor planning that result in subtle effects on performance in younger children with ASD that become more pronounced with age.
Highlights
Autism spectrum disorder (ASD) is characterized by impairments in social communication, restricted interests, and/or repetitive behaviors (American Psychiatric Association [APA], 2013)
The three-way interaction suggests that pattern of initiation time (IT) and movement time (MT) among the groups differed as a function of age and task complexity
While typically developing children generally improve in their motor performances as they age, there may be different developmental trajectories for simple versus complex motor skills across the lifespan in children and youth with ASD, as tasks become more complex and learning curves come into play
Summary
Autism spectrum disorder (ASD) is characterized by impairments in social communication, restricted interests, and/or repetitive behaviors (American Psychiatric Association [APA], 2013). In addition to these core symptoms, individuals on the autism spectrum demonstrate a diverse set of motor impairments (for reviews, see Fournier et al, 2010; Sacrey et al, 2014). A delay in the development of fine motor skills between the ages of 6–24 months was predictive of which high-risk infants later received an ASD diagnosis (Landa and Garrett-Mayer, 2006; Landa et al, 2013; Choi et al, 2018). Reaching and grasping skills may be especially important to investigate in ASD, as poor reaching and grasping skills may detrimentally impact an infant’s ability to manually explore and learn about the world around them (Libertus et al, 2014)
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