Movement preparation in adults with and without Down syndrome.

This study was designed to determine whether adults with mental retardation, with and without Down syndrome, display flexibility in the preparation of limb movements. A four-alternative target-aiming task involving movements with either the right or left hand to near or far targets was employed. Prior information about the movement to be made was manipulated by precuing specific features. Although reaction times and movement times were longer for subjects with than for those without mental retardation, the pattern of results was similar. Specifically, both retarded groups were able to use advance information to reduce movement preparation time. Moreover, information about movement distance was useful to subjects whether or not hand was precued. This finding indicates that the individuals with mental retardation were not limited by a fixed-order movement preparation process.