Basic study on trajectories of reaching movements in children with learning disabilities

A number of children with learning disabilities (LD) are not good at visuomotor control. In this study, we analyzed hand trajectories and joint angles during reaching movement tasks under rotated visual feedback in subjects with and without LD. The error in ballistic movement was determined by measuring the angle between the direction in which the subject started to reach out and the direction of the target (error angle), and the error in corrective movement was determined by measuring the area between the trajectory and a straight line drawn between the starting point and the end point (error area). In the initial movement when the visual field had been rotated 30 deg, error angles were about -30 deg in both the LD and normal groups; however, the error area was 2.9 cm² greater in the LD group than in the normal group. On the other hand, joint paths of the shoulder in reaching the same target tended to change in the LD group. These results suggested that the LD subjects had worse skills in corrective movement than did the normal subjects and that adaptation by the LD subjects occurred more slowly than that by the normal subjects.