Shift of manual preference by lateralized practice generalizes to related motor tasks

Previous investigation (Teixeira and Teixeira in Brain Cogn, in press, 2007) has evidenced a persistent shift of manual preference for a particular motor task following lateralized practice. In the present study, we assessed the extent to which shift of manual preference is generalizable to related motor tasks. Twenty right-handers were assigned to an experimental or to a control group. The former were provided with practice on a particular sequence of finger movements with their left hand only, while the latter remained inactive. Participants were assessed on manual asymmetry, indexed by movement time, and manual preference for the practiced and for other two sequences of finger movements (transfer tasks). Assessment was made before, immediately after, and 30 days following (retention) practice sessions. Results showed that lateralized practice led to significant bilateral reduction of movement time, maintaining the symmetric performance observed before practice following task acquisition. Regarding manual preference, before task acquisition, all participants in the experimental group were right-handed for the main task; immediately after practice their predominant manual preference shifted to the left hand, a profile that was maintained in retention. This persistent shift of manual preference was also observed for one of the transfer tasks requiring the same sequence of transitions between finger movements. Indices of correlation between manual asymmetry and manual preference were non-significant across tasks and phases, suggesting that manual preference was not defined by lateral asymmetry of performance. We propose that manual preference is established by automatic sensorimotor processing and/or increased confidence on a single hand from previous experiences.