Manual asymmetries in the performance of sequential movement by adolescents and adults with Down syndrome.

Movement-sequencing deficits and possible manual-performance asymmetries in right-handed adolescents and adults with Down syndrome were examined. In Experiment 1, subjects with Down syndrome and retarded and nonretarded control subjects finger-tapped with both hands. Although both retarded groups finger-tapped more slowly than did nonretarded subjects, the two retarded groups did not differ. Subjects with Down syndrome, however, failed to show a manual performance asymmetry in favor of the right hand. In Experiment 2, a finger-tapping task and a cross-hand transfer of training paradigm were used to examine hemispheric dominance for movement sequencing. Although subjects with Down syndrome again showed no hand differences in tapping performance, they evidenced the same transfer of training asymmetries as did subjects without Down syndrome, suggesting that both the subjects with Down syndrome and the control subjects had a left-hemisphere dominance for movement sequencing.