Early development of reaching in Down syndrome infants

The development of reaching was studied in 10 Down syndrome and 10 control infants. Arm movements were recorded at 5, 7 and 9 months for the control group and 7, 9 and 11 months for the group with Down syndrome. Arm movements were recorded using a 3-dimensional video-motion analysis system. In both groups, there was a change from bilateral to unilateral responses with age, although Down syndrome infants used bilateral responses longer. Arm velocity increased significantly with age in the control group, but not in the Down syndrome group. Several characteristics of the reaching movements were clearly different between the Down syndrome and control groups. The deviations from a straight line and the changes in the plane of motion suggest that Down syndrome infants have more difficulty in controlling their arm movements. As expected, the results indicate the presence of a delay in the development of reaching in Down syndrome infants. They also suggest the presence of a deficit in the organization of their reaching movement.