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Deanna Kennedy, M.S.

The ability to coordinate movements between the limbs is important for many activities of daily living and sport specific skills. For example, tying your shoes, slicing bread, driving your car, and serving a tennis ball are tasks that involve some type of coordination between the limbs. However, the role of each limb may vary with different task requirements. Some tasks, such as clapping your hands, require the limbs to produce mirror movements in both time and space. Other tasks may require different movements between the limbs to achieve the task goal, such as tying your shoes or serving a tennis ball. Still other tasks may require one limb to act as a stabilizer while the other limb performs a specific movement such as slicing bread or shooting a bow and arrow. Although these examples of bimanual movements are relatively easy, other coordination patterns can be quite difficult. Bimanual tasks like playing the piano or guitar, for example, underscore the difficulty that can be associated with coordinating the limbs. Why then are some bimanual coordination patterns easy to perform while other patterns are difficult or even impossible to perform?

            One possible explanation may be neural crosstalk. Crosstalk is defined as a mirror image command sent to muscles of the opposite limb. To coordinate movements between the limbs, the brain sends a command signal to each limb to produce a specific action. One signal is sent to the right limb while another is sent to the left limb. Crosstalk occurs when part of the signal is sent to the opposite limb. This is not typically a problem when the actions of the limbs are symmetric because the signals contain the same information. However, when the task requires asymmetric movements between the limbs, the bimanual movements may suffer from ongoing interference due to conflicting information or a partial intermingling of the signals controlling the arms.

            Recent research, however, has demonstrated that we can overcome the interference between the limbs when integrated feedback is provided. Integrated feedback, in this case, provides visual information from the left and right limb as a single point.  For example, video games often provide this type of feedback.  One hand may control movement of the character from left to right while the other hand may control up and down, but the feedback provided is simply the movement of the character. Kovacs and Shea provided this type of information in their study examining bimanual coordination. Participants were required to perform 5:3 multi-frequency bimanual coordination patterns. This type of pattern would require you to move one limb five times for every three movements of the opposite limb.  Previous research has shown such a coordination pattern difficult or near impossible for a person without musical training.  However, when Kovacs and Shea provided integrated information participants were able to quickly and easily perform the complicated patterns. It is believed that the integrated information reduced attentional demands by permitting subjects to focus on a single point rather than splitting attention between the two limbs.

Further Reading:

1.  Kovacs AJ, Buchanan JJ, Shea CH (2010) Impossible is nothing: 5:3 and 4:3 multi-frequency bimanual coordination. Exp Brain Res; 201: 249-259.

2.  Kennedy DM, Boyle JB, & Shea CH (2013). The role of auditory and visual models in the production of bimanual tapping patterns. Exp Brain Res;  224: 507-518.

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