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Structure of joint variability in bimanual pointing tasks
Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
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2002 (English)In: Experimental Brain Research, ISSN 0014-4819, Vol. 143, no 1, 11-23 p.Article in journal (Refereed) Published
Abstract [en]

Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.

Place, publisher, year, edition, pages
2002. Vol. 143, no 1, 11-23 p.
Keyword [en]
Coordination, Variability, Voluntary movement, Bimanual, Human
URN: urn:nbn:se:umu:diva-4445DOI: 10.1007/s00221-001-0944-1PubMedID: 11907686OAI: diva2:143558
Available from: 2005-03-31 Created: 2005-03-31Bibliographically approved
In thesis
1. Perception and control of upper limb movement: Insights gained by analysis of sensory and motor variability
Open this publication in new window or tab >>Perception and control of upper limb movement: Insights gained by analysis of sensory and motor variability
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chronic neck-shoulder pain is associated with impairments of proprioception and motor control. Thus, assessment of proprioceptive and motor function may be powerful tools both for research and clinical practice. However, insufficient knowledge of certain features of human sensorimotor control hampers both development and interpretation of results of clinically relevant tests. For example, evidence is lacking which proprioception submodalities are reflected in common tests of proprioception. For testing motor function, a better understanding of the control of goal directed arm movements is needed. The purpose of the thesis was to gain further insights into the sensorimotor control of the upper limb in healthy subjects, with implications for clinical testing. The main aims were: (1) to study relationships of outcomes of different tests of shoulder proprioception and (2) to study control strategies in bimanual pointing tasks by analysis of the structure of joint angle variability with the Uncontrolled Manifold (UCM) method. Correlations between proprioceptive acuity in different variants of ipsilateral position-matching and velocity-discrimination were studied. The main finding was that two uncorrelated mechanisms based either on perception of position or movement might underlie perception of limb location in ipsilateral position-matching. The results provided important information for interpretation of common and development of novel tests of shoulder proprioception. The structure of joint angle variance was computed with respect to several task variables during bimanual pointing. Joint angle variability was decomposed in variance affecting and not affecting a task variable. The results showed that the variance in joint space was structured according to the predictions of the UCM hypothesis. It was also shown that the arms were united into one synergy to significantly larger degree than joints within each arm were united into single-arm synergies. It was concluded that the UCM approach might quantify components of motor variability during repetitive motor tasks.

Place, publisher, year, edition, pages
Umeå: Kirurgisk och perioperativ vetenskap, 2005. 51 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 953
Medicine, proprioception, kinaesthesia, position sense, movement sense, position-matching, velocity-discrimination, correlation, uncontrolled manifold, variability, synergy, upper limb, motor control, Medicin
National Category
Sport and Fitness Sciences
Research subject
urn:nbn:se:umu:diva-485 (URN)91-7305-850-5 (ISBN)
Public defence
2005-04-12, Stora salen, Arbetslivsinstitutet / Belastningsskadecentrum, Petrus Lästadius väg, Umeå, 13:00 (English)
Available from: 2005-03-31 Created: 2005-03-31 Last updated: 2015-01-21Bibliographically approved

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