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Ida Maria Bosga-Stork, Jurjen Bosga and Ruud G.J. Meulenbroek

This longitudinal study examined the movement efficiency of typically developing children between 7 and 9 years of age by scrutinizing their movement amplitudes and frequencies as they settled into a loop-writing task in which both parameters were prescribed. It was hypothesized that during the first three grades at primary school children would show increasing efficiency in exploiting the inverse relationship between movement amplitude and frequency when adjusting their movement errors. Whereas a clear developmental trend showed increasing efficiency with respect to the way in which the primary school children met the amplitude constraints, a more variable pattern was found for the age-dependent adjustments to the frequency requirements. At the level of parameter-error corrections from one cycle to the next, a marginal developmental trend was observed. Results are discussed in terms of contrasting effects between educational targets and movement-efficiency principles.

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Ida M. Bosga-Stork, Jurjen Bosga and Ruud G.J. Meulenbroek

The development of the ability to adapt one’s motor performance to the constraints of a movement task was examined in a longitudinal study involving 7 to-9-year-old children who were asked to perform a preparatory handwriting task. The capacity for sensorimotor synchronization was captured by the standard deviation of the relative phase between pacing signals and writing movements and the capacity to adjust wrist-finger coordination while performing repetitive movements was analyzed by autocorrelations of the vertical pen-tip displacements. While the capacity for synchronization improved with age, the autocorrelations were positive at short time lags only and hardly changed with age. A measure of “the long-term memory” of time series (Hurst exponent) confirmed that the findings were systematic rather than noise. Collectively, the results indicate that flexible movement strategies emerge early on in the first 3 years of formal handwriting education. Implications for educational and clinical practice are considered.

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Jurjen Bosga and Ruud G. J. Meulenbroek

In this study we investigated redundancy control in joint action. Ten participantpairs (dyads) performed a virtual lifting task in which isometric forces needed to be generated with two or four hands. The participants were not allowed to communicate but received continuous visual feedback of their performance. When the task had to be performed with four hands, participants were confronted with a redundant situation and between-hand force synergies could, in principle, be formed. Performance timing, success rates, cross-correlations, and relative phase analyses of the force-time functions were scrutinized to analyze such task-dependent synergies. The results show that even though the dyads performed the task slower and less synchronized in the joint than in the solo conditions, the success rates in these conditions were identical. Moreover, correlation and relative phase analyses demonstrated that, as expected, the dyads formed between-participant synergies that were indicative of force sharing in redundant task conditions.

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Jurjen Bosga, Ruud G. J. Meulenbroek and Raymond H. Cuijpers

In this study, we investigate how two persons (dyads) coordinate their movements when performing cyclical motion patterns on a rocking board. In keeping with the Leading Joint Hypothesis (Dounskaia, 2005), the movement dynamics of the collaborating participants were expected to display features of a prime mover with low movement variability. Fourteen subject pairs performed the task in nine amplitude-frequency combinations that were presented in the form of a to-be-tracked stimulus on a computer display. Participants were asked to track the stimulus by jointly rocking the Board sideways while receiving continuous visual feedback of its rotations. Displacements of 28 IREDS that were attached to the rocking board, both ankles, knees, hips, shoulders and heads of both actors, were sampled at 75 Hz by means of a 3D-motion tracking system. From these data, we derived body-segment angular excursions as well as the continuous relative phase and time-lagged cross-correlations between relevant joint excursions. The results show that, at the intrapersonal level, knee rotations initially led all other joints in time while the antiphase coordination between the knees displayed relative low variability. At the interpersonal level, dyads adopted a leader-follower strategy with respect to the coordination demands of the task. We take that knee rotations create a dynamic foundation at both intra- and interpersonal levels involving subordination of individual action to joint performance thereby allowing for low-dimensional control of joint action in a high-dimensional, repetitive motor task.