The Acquisition of Movement Skills: Practice Enhances the
Dynamic Stability of Bimanual Coordination

Christopher J. Smethurst & Richard G. Carson

Perception and Motor Control Laboratory, Department of Human Movement Studies,
The University of Queensland, Brisbane, Australia


During bimanual movements, two relatively stable "inherent" patterns of coordination (in-phase and anti-phase) are displayed (e.g., Kelso 1984). Recent research has shown that new patterns of coordination can be learned. For example, following practice a 90 degree out-of-phase pattern can emerge as an additional, relatively stable, state (e.g., Zanone & Kelso, 1992). On this basis, it has been concluded that practice leads to the evolution and stabilisation of the newly learned pattern and that this process of learning changes the entire attractor layout of the dynamic system. A general feature of such research has been to observe the changes of the targeted pattern’s stability characteristics during training at a single movement frequency.

The present study was designed to examine how practice affects the maintenance of a coordinated pattern as movement frequency is scaled. Eleven volunteers were asked to perform a bimanual forearm pronation-supination task. Time to transition onset was used as an index of the subjects’ ability to maintain two symmetrically opposite coordinated patterns (target task: 90 degrees out-of-phase; transfer task: 270 degrees out-of-phase). Their ability to maintain the target task and the transfer task were examined again after five practice sessions each consisting of 15 trials of only the 90 degree out-of-phase pattern. Concurrent performance feedback (Lissajous figure) was available to the participants during each practice trial.

A comparison of the time to transition onset showed that the target task was more stable after practice (p<.025). These changes were still observed one week (p<.05) and two months (p<.075) after the practice period. Changes in the stability of the transfer task were not observed until two months after practice (p<.025). Notably, following practice, transitions from the 90 degree pattern were generally to the anti-phase (180 degrees) pattern. Whereas, transitions from the 270 degree pattern were to the 90 degree pattern.

These results suggest that practice does improve the stability of a 90 degree pattern, but do not necessarily support the notion that such improvements are transferable to the performance of a 270 degree pattern. In addition, the anti-phase pattern remained more stable than the practiced 90 degree pattern throughout.