Anticipatory task-related modifications in reach: age-related changes and implications for children with DCD

Abstract

Reaching and grasping actions situated in the context of sequential actions can give useful knowledge pertaining to skillful acquisition of a task goal. The aim of this dissertation was to investigate the development of upper extremity skills in the performance of sequential actions in healthy young adults and typically developing (TD) children and apply this knowledge to determine the impairments of motor control in children with Developmental Coordination Disorder (DCD). A 6-camera Vicon system was used to record kinematics of upper limb actions when reaching-to-point, reaching-to-grasp, reaching-to-grasp-and-lift, and reaching-to-grasp-lift-and-place objects with either hand. In the first study, we investigated the control of sequential actions in adults to provide a baseline for `skillful' performance, with respect to feedforward control and reliance on online modifications to achieve the task goal. In addition, we also investigated performance differences attributable to manual asymmetry. We found that anticipatory modifications were present in both feedforward control and feedback elements of the reach and that the non-preferred hand was inferior only in feedback elements. In the first experiment of second study, we investigated the emergence of age-related differences in typically developing children (5-11 years) in their acquisition of improved control of sequential actions. In the TD children, all age groups of children showed task-specific changes in online modifications during the reach phase, but feedforward control was not adult-like at 11 years. The lateralization trajectory showed non-linear developmental trends and high within-group variability. In the second experiment of second study, we compared the performance of 9-11 year-old children with DCD in comparison with the profile of developmental landscape of TD children. Our results suggest that children with DCD are similar in performance to 6- and 8-year-olds, in their inability to plan and execute a movement sequence as a whole or to show asymmetry. The results point towards an inability to incorporate online modifications, and a possible developmental delay in coordination of sequential actions in children with DCD.