The perceptual-motor impairments of individuals with Down syndrome (DS) are attributed to central (e.g., neurophysiology deficits that affect the retrieval or initiation of motor programs) and peripheral (e.g., anatomical deficits relating to issues with inertia of limb mechanics and muscle organization) processes. However, recent research suggests that central deficits do not affect the integration between movements. We investigate the impact of central and peripheral DS deficits on movement integration by examining the planning and execution of multiple-target multiple-arm movements. Individuals with DS, typically developing (TD), and individuals with an undifferentiated intellectual disability (UID) completed five aiming tasks: a one target; a one-arm, two-target extension; a two-arm, two-target extension (movement one was performed with one arm and movement two performed with the other); a one-arm, two-target reversal; and a two-arm, two-target reversal. Movement times (MTs) to the first target were longer in the two-target tasks compared with the one-target task. For the one-arm, two-target reversal task, this effect emerged only in individuals with DS. These results indicate that individuals with DS use central processing for movement integration similarly to their TD and UID counterparts but cannot exploit peripheral-level integration to enhance integration in one-arm reversal tasks.
Reilly is with the Dept. of Sport and Outdoor Exercise Science, University of Derby, Derby, England. Lawrence and Mottram are with the School of Sport, Health, and Exercise Sciences, Bangor University, Bangor, Wales. Kahn is with the Dept. of Kinesiology, University of Windsor, Windsor, ON, Canada.