Free(z)ing Degrees of Freedom in Skill Acquisition

Vereijken, Beatrix; Emmerik, Richard E.A. van; Whiting, H. T. A.; Newell, Karl M.

doi:10.1080/00222895.1992.9941608

Cited by 462 publications

(252 citation statements)

References 18 publications

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“…Practice is expected to lead to a change in the average magnitude of such variables (commonly, maximize or minimize them) and a drop in their variability. Effects of motor learning on coordination within multi-element systems has been discussed within the classical Bernstein scheme of stages such as freezing and releasing degrees-of-freedom (Bernstein 1996;Vereijken et al 1992;Newell et al 2003). …”

Section: Implications For the Field Of Motor Learningmentioning

confidence: 99%

Learning effects on muscle modes and multi-mode postural synergies

et al. 2007

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We used the framework of the uncontrolled manifold hypothesis to explore the effects of practice on the composition of muscle groups (M-modes) and multi-M-mode synergies stabilizing the location of the center of pressure (COP). In particular, we tested a hypothesis that practice could lead to a transition from co-contraction muscle activation patterns to reciprocal patterns. We also tested a hypothesis that new sets of M-modes would form stronger synergies stabilizing COP location. Subjects practiced load release tasks for five days while standing on a board with a narrow support surface ("unstable board"). Their M-modes and indices of multi-M-mode synergies were computed during standing without instability and during standing on an unstable board before practice, in the middle of practice, and at the end of practice. During standing without instability, subjects showed two consistent M-modes uniting dorsal and ventral muscles of the body respectively (reciprocal modes). While standing on an unstable board, prior to practice, subjects commonly showed M-modes uniting muscle pairs with opposing actions at major leg joints -co-contraction modes. Such sets of M-modes failed to stabilize the COP location in the anterior-posterior direction. Practice led to better task performance reflected in fewer incidences of lost balance. This was accompanied by a drop in the occurrence of co-contraction M-modes and the emergence of multi-mode synergies stabilizing the COP location. We conclude that the central nervous system uses flexible sets of elemental variables (modes) to ensure stable trajectories of important performance variables (such as COP location). Practice can lead to adjustments in both the composition of M-modes and M-mode covariation patterns resulting in stronger synergies stabilizing COP location.

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Section: Implications For the Field Of Motor Learningmentioning

confidence: 99%

Learning effects on muscle modes and multi-mode postural synergies

et al. 2007

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“…are not eliminated or frozen (cf. Bernstein 1967;Vereijken et al 1992) but are always all used to assure both stable and flexible performance of important variables. Synergies (structural units) represent neural organizations that produce a stable output variable by a coordinated action of many elements.…”

Section: Hierarchies Of Synergies In Natural Movementsmentioning

confidence: 99%

Hierarchies of synergies: an example of two-hand, multi-finger tasks

2006

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We explored the ability of the central nervous system (CNS) to assemble synergies stabilizing the output of sets of effectors at two levels of a control hierarchy. Specifically, we asked a question: can the CNS organize both two-hand and within-a-hand force stabilizing synergies in a simple two-hand force production task that involves two fingers per hand? Intuitively, one could expect a positive answer; that is, forces produced by each hand are expected to co-vary negatively across trials to bring down the total force variability, while forces produced by each finger within-a-hand are expected to co-vary negatively to reduce the variability of that hand's contribution to the total force. The subjects were instructed to follow a trapezoidal time profile with the signal corresponding to the force produced by a set of instructed fingers in one-hand tasks with two-finger force production and in two-hand tasks with involvement of both symmetrical and asymmetrical finger pairs in the two hands. Finger force co-variation across trials was quantified and used as an index of stabilization of the force produced by all the instructed fingers, and of the force produced by finger pairs within-a-hand. No major differences were seen between the dominant and the non-dominant hand and between the twohand tasks with symmetrical and asymmetrical finger involvement. Stronger synergies were seen in the index-middle finger pair as compared to the ring-little finger pair. The main result of the study is the significantly weaker or even lacking two-finger force stabilizing synergies within-a-hand during two-hand tasks while such synergies were present in one-hand tasks. This observation points at a potential limitation in the ability of the CNS to organize synergies at two levels of a control hierarchy simultaneously. It also allows suggesting a hypothesis on two types of synergies in the human motor repertoire, well-practiced synergies that form a library serving as the foundation for all novel actions, and freshly assembled synergies.

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“…Although some evidence supporting this hypothesis is provided by a number of kinematic studies of learning tasks (McDonald et al 1989;Smith et al 2001;Vereijken et al 1992), contradictory results have been reported (Caillou et al 2002;Ko et al 2003). Moreover, experimentally, the proposed "elimination of DOFs" has typically meant a reduction in the range of joint motion (Vereijken et al 1992), in which case no DOFs are actually eliminated. Thus, evidence for the proposed 'freezing-freeing' hypothesis is weak at best.…”

Section: Introductionmentioning

confidence: 99%

The role of kinematic redundancy in adaptation of reaching

2006

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Although important differences exist between learning a new motor skill and adapting a well-learned skill to new environmental constraints, studies of force field adaptation have been used frequently in recent years to identify processes underlying learning. Most of these studies have been of reaching tasks that were each hand position was specified by a unique combination of joint angles. At the same time, evidence has been provided from a variety of tasks that the central nervous system takes advantage of the redundancy available to it when planning and executing functional movements. The current study attempted to determine whether a change in the use of joint motion redundancy is associated with the adaptation process. Both experimental and control subjects performed 160 trials of reaching in each of four adaptation phases, while holding the handle of a robot manipulandum. During the first and last adaptation phases, the robot motors were turned off. During phases 2 and 3 the motors produced a velocity-dependent force field to which experimental subjects had to adapt to regain relatively straight line hand movements during reaching to a target, while the motors remained off for the control group. The uncontrolled manifold (UCM) method was used to partition the variance of planar clavicle-scapular, shoulder, elbow and wrist joint movements into two orthogonal components, one (V UCM ) that reflected combinations of joint angles that were equivalent with respect to achieving the average hand path and another (V ORT ) that took the hand away from its average path. There was no change in either variance component for the control group performing 640 nonperturbed reaches across four 'pseudo-adaptation' phases. The experimental group showed adaptation to reaching in the force field that was accompanied initially by an increase in both components of variance, followed by a smaller decrease of V UCM than V ORT during 320 practice reaches in the force field. After initial re-adaptation to reaching to the null field, V UCM was higher in experimental than in control subjects after performing a comparable number of reaches. V UCM was also larger in the experimental group after re-adaptation when compared to the 160 null field reaching trials performed prior to initial force field introduction. The results suggest that the central nervous system makes use of kinematic redundancy, or flexibility of motor patterns, to adapt reaching performance to unusual force fields, a fact that has implications for the hypothesis that motor adaptation requires learning of formal models of limb and environmental dynamics.

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Free(z)ing Degrees of Freedom in Skill Acquisition

Cited by 462 publications

References 18 publications

Learning effects on muscle modes and multi-mode postural synergies

Learning effects on muscle modes and multi-mode postural synergies

Hierarchies of synergies: an example of two-hand, multi-finger tasks

The role of kinematic redundancy in adaptation of reaching

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