chapter
Training Effects on Coupling Strength in Bimanual Rhythmic Performance
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It has been suggested that learning to bimanually perform complicated rhythms involves a decrease of interaction between the hands (e.g., Shaffer, 1981; Yamanishi, Kawato, & Suzuki, 1980), so that each hand's performance becomes less dependent on the activity of the other hand. If the two hands are modeled as a system of two nonlinearly coupled nonlinear oscillators, under the assumption that the characteristics of the unit oscillators are not changing (cf., Haken, Kelso, & Bunz, 1985), oscillator theory indeed reveals that a decreasing coupling strength (K) between the two oscillators results in an increasing number of accessible frequencyor mode-locked regions ("Arnol'd tongues"), representing the frequency ratios that can be performed succesfully. This implies that if subjects are unable to perform a certain frequency ratio, a decrease in the strength of coupling might make the required mode locking possible. However, for smaller values of K the performance is less stable, because the corresponding widths of the mode-locked regions are smaller. It is, therefore, to be expected that, once the required rhythm can be performed, training will not lead to further decrease of K. It is even possible that K will increase, thereby enhancing the stability of performance.