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- Domkin, Dmitry, et al.
(författare)
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Joint angle variability in 3D bimanual pointing : uncontrolled manifold analysis.
- 2005
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Ingår i: Experimental Brain Research. - : Springer Science and Business Media LLC. - 0014-4819 .- 1432-1106. ; 163:1, s. 44-57
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Tidskriftsartikel (refereegranskat)abstract
- The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V(COMP)) and affecting (V(UN)) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R(V)=V(COMP)/V(UN) served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R(V) values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R(V). Both V(COMP) and V(UN) variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.
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| 3. |
- Laczko, Jozsef, et al.
(författare)
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Stabilization of kinematic variables in the control of bimanual pointing movements
- 2001
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Ingår i: Proceedings of the International joint conference on neural networks. ; , s. 1256-1260
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Konferensbidrag (refereegranskat)abstract
- Human voluntary movements face a problem of kinematic redundancy: The number of degrees of freedom for the peripheral mechanical apparatus (e.g., a Iimb) is higher than the number of variables necessary to describe movement execution. Thus, there is an infinity of different ways to execute a given motor task. The recently developed Uncontrolled Manifold (UCM) hypothesis suggests that the central nervous system (CNS) generates solutions such that important task related variables are selectively stabilized. Each motor task is associated with stabilizing a .time series of a task variable. At each instant, the CNS selects, in the state space af elements participating in the task, a manifold (UCM) corresponding to a fixed value of the selected task variable. We study a planar bìmanual task, when one hand moves a target and the other hand moves a pointer that must reach the target. We hypothesized that the stabilized task variable was the vectorial difference of the pointertip and the target. The 6 dimensional state space was defined bys 'joint configuration vectors" whose elements were intersegmental joint angles (shoulder, elbow and wrisst in both arms). The subjects repeated the movements IS times, and the movements were recorded by a movement analysis system. Then, the subjects practiced the movements (300 trials). After practice IS trials were recorded again. We computed the variance of the joint configurations before and after practice. Six joint rotations affected the 2 dimensional task variable. The UCM corresponding to this variable is 4- dimensional, while the subspace of the state space that is orthogonal (ORT) to the UCM is 2-dimensional. The variance within the UCM was larger than in the ORT conforming to the UCM hyphothesis. After practice the joint variance decreased and the drop in the component of variance that did not affect the task vaeriable was larger thnn the drop 'of the other component. Thus, practice lead to more stable time courses of the task variable and of the corresponding joint configuration.
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