Motor Control (Feldman): BBS Call for Commentators

[Stevan Harnad]

    Below is the abstract of a forthcoming target article by:
                A.G. Feldman & M.F. Levin
                        on:
        POSITIONAL FRAMES OF REFERENCE IN MOTOR CONTROL

This article has been accepted for publication in Behavioral and Brain
Sciences (BBS), an international, interdisciplinary journal providing
Open Peer Commentary on important and controversial current research in
the biobehavioral and cognitive sciences.

Commentators must be current BBS Associates or nominated by a current
BBS Associate. To be considered as a commentator for this article, to
suggest other appropriate commentators, or for information about how to
become a BBS Associate, please send email to:

harnad at clarity.princeton.edu  or harnad at pucc.bitnet        or write to:
BBS, 20 Nassau Street, #240, Princeton NJ 08542  [tel: 609-921-7771]

To help us put together a balanced list of commentators, please give
some indication of the aspects of the topic on which you would bring
your areas of expertise to bear if you were selected as a commentator.
An electronic draft of the full text is available for inspection by
anonymous ftp according to the instructions that follow after the abstract.
____________________________________________________________________

    POSITIONAL FRAMES OF REFERENCE IN MOTOR CONTROL: ORIGIN AND USE

        Anatol G. Feldman (1,2,4) & Mindy F. Levin (2,3,4)
    Institute of Biomedical Engineering, University of Montreal (1)
    Research Centre, Rehabilitation Institute of Montreal, H3S 2J4 (2)
    School of Rehabilitation, University of Montreal (3)
    Centre for Research in Neurological Sciences, University of Montreal (4)
                EMAIL:Feldman at ere.umontreal.ca 

    KEYWORDS: motor control, frames of reference, motoneurons, control
    variables, proprioception, kinaesthesis, equilibrium points,
    multi-muscle systems, pointing, synergy, redundancy problem.

    ABSTRACT: A hypothesis about sensorimotor integration (the lambda
    model) is described and applied to movement control and
    kinesthesia.  The nervous system organizes positional frames of
    reference for the sensorimotor apparatus and produces active
    movements by shifting frames in terms of spatial coordinates.
    Kinematic and electromyographic patterns are not programmed but
    emerge from the dynamic interaction of the system's components,
    including external forces, within the designated frame of
    reference. Motoneuronal threshold properties and proprioceptive
    inputs to motoneurons may be important components in the
    physiological mechanism which produces positional frames of
    reference.  The hypothesis that intentional movements are produced
    by shifting the frame of reference is extended to multi-muscle and
    multi-degrees of freedom systems by providing a solution for the
    redundancy problem the allows the control of a joint alone or in
    combination with other joints to produce any desired limb
    configuration and movement trajectory. For each motor behavior, the
    nervous system uses a strategy which minimizes the number of
    changeable control variables and keep sthe parameters of these
    changes invariant. This is illustrated by examples of simulated
    kinematic and electromyographic signals from single- and
    multi-joint arm movements produced by patterns of control
    variables. Empirical support is provided and additional tests are
    suggested. The model is contrasted with others based on the ideas
    of programming of motoneuronal activity, muscle forces, stiffness
    or movement kinematics.

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