Kinematic characteristics of reaching in children with Down Syndrome

Movement abnormalities observed in children with Down Syndrome (DS) may arise from difficulties in perceiving or using relevant task cues for planning actions. Kinematic characteristics of reaching in 8-10-year-old DS children were investigated and compared with normally developing children, matched in chronological (CA-C) and in developmental (DA-C) age. Task cues were varied by manipulating size (little, big) and function of objects (hold, place, throw). Reaching actions were recorded using OPTOTRAK. Compared to control children, particularly CA-C, DS subjects moved more slowly and their wrist trajectories varied considerably over trials. The proportion of total movement time in deceleration was greater and less smooth (more movement units) for DS children. This may reflect feedback guidance to correct spatial inaccuracy of the reach or difficulties in grasping. While there were no systematic group differences in kinematic features as a function of task cues, trajectory shapes of DS children were least variable when reaching was followed by a low-precision task when context was available (throw). Possible explanations of these findings are considered.