Lateral asymmetries in arm, wrist and finger movements.

On the assumption of contralateral control, lateral asymmetries in motor performance are often associated with the functional specialization of the cerebral hemispheres. However, anatomical as well as previous behavioral studies, indicate this assumption may not be valid for all joints of the limbs. To test this assumption, right-handed male subjects performed a rapid tapping task using movements of the index finger, the wrist, or the shoulder. The hand used and order of conditions were counterbalanced across subjects. The rate and variability data were submitted to a 2 x 3 (hand x joint) Analysis of Variance with repeated measures on both factors. For both rate and variability significant (all p less than .01) main effects were evident for hand and joint with no significant interactions. It is argued that the variability of tapping reflects the processing mode of the contralateral hemisphere and thus leads to the conclusion that crossed pathways are the principal mechanism for controlling rapid movements of all limb joints. It is tentatively concluded that where either crossed or ipsilateral pathways are available, the type of movement control required will dictate which pathway is used.