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Yeou-Teh Liu, Tsung-Yu Hsieh and Karl M. Newell

Recent studies have shown more than one time scale of change in the movement dynamics of practice. Here, we decompose the drift and diffusion dynamics in adaptation to performing discrete aiming movements with different space-time constraints. Participants performed aiming movements on a graphics drawing board to a point target at 5 different space-time weightings on the task outcome. The drift was stronger the shorter the time constraint whereas noise was U-shaped across the space-time conditions. The drift and diffusion of adaptation in discrete aiming movements varied as a function of the space-time constraints on performance outcome and the spatial, temporal, or space-time measure of performance outcome. The findings support the postulation that the time scale of movement adaptation is task dependent.

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I-Chieh Lee, Yeou-Teh Liu and Karl M. Newell

We investigated the coordination of balance and propulsion processes in learning to ride a unicycle through a principal component analysis (PCA) of the nature and number of functional degrees of freedom (DOF) in the movement coordination patterns. Six participants practiced unicycle riding on an indoor track for 28 sessions over separate days. The movement time and performance outcomes were recorded for each trial and body segment kinematics were collected from the first and every succeeding 4th session. The first appearance of no-hand-support performance varied across participants from the 5th practice session to the 22nd session. The PCA showed that initially in practice the 39 kinematic time series could be represented by 6–9 components that were reduced over practice to 4–7 components. The loadings of the PCA that reflected balance and propulsion processes became more coupled as a function of successfully riding the unicycle. The findings support the proposition that learning to ride the unicycle is a process of making the system more controllable by coordinating balance and propulsion while mastering the redundant DOF.