Interference effects between manual and oral motor skills.

Consolidation of a motor skill is characterized by spontaneous improvement in performance between practice sessions. These offline gains can be eliminated if another skill is introduced soon afterward-a phenomenon called retroactive interference. Interference effects have been found in studies using two similar tasks involving the same motor effectors in a manual mode. The present study aimed to determine the extent to which differences in motor production mode modulate interference in skill learning. Healthy participants were assigned to one of three conditions and trained on a finger opposition sequence (FOS) learning task. All subjects were tested 24 h later on the original FOS learning task. Control subjects who were not exposed to a secondary learning task exhibited the expected offline gains after 24 h. Subjects who immediately learned a secondary task after the FOS training, either in the same manual mode (French Sign Language) or in an oral mode (CVC syllables), did not show any offline gains. Interestingly, the amount of interference was equivalent in the manual and oral learning conditions. The results reveal that interference effects in motor skill learning can occur when different effectors are involved in the primary and secondary tasks. The sequence processing abilities of the basal ganglia appear to play a major role in these interference effects.