Control of associated movement as a factor influencing reaction times of mentally retarded adults.

In choice reaction time (RT) tasks, the response of the appropriate finger by mentally retarded subjects is often accompanied by associated movements of responding and nonresponding fingers. To determine of the effects of such associated movements, we compared RTs in two conditions. When all fingers were kept in close proximity to their appropriate keys by fingers restraints, retarded subjects' RTs showed a small but significant improvement compared with those for an unrestrained condition. Nonretarded subjects showed no difference. This result suggests that difficulty in controlling associated movements of responding and nonresponding fingers contributes to the slower RTs of retarded persons. Possible mechanisms underlying this difficulty were discussed.