Frith and Frith (1974) suggested that adults with Down syndrome have difficulty planning goal-directed movements and therefore are more reliant on feedback than other mentally disabled people. The purpose of the study was to examine this hypothesis directly through the manipulation of visual feedback. Twelve adults with Down syndrome, 12 mentally disabled adults without Down syndrome, and 12 nondisabled adults performed simple aiming movements to targets of three different diameters. While the target was always visible, on half the trial blocks vision of the movement was occluded upon response initiation. Subjects with Down syndrome exhibited longer movement times than other subjects, regardless of vision condition. In terms of target-aiming consistency, subjects with Down syndrome were actually less affected by the elimination of visual feedback than subjects in the other mentally disabled group. While adults with mental disabilities appear to be more reliant on visual feedback for the control of goal-directed movement, this dependence is not a specific characteristic of Down syndrome.
The authors are with the Department of Kinesiology, McMaster University, Hamilton, ON, Canada L8S 4K1.