Behav. Brain Sci. Call for Commentators: Motor Control

[Stevan Harnad]

Below is the abstract of a forthcoming target article to appear in
Behavioral and Brain Sciences (BBS), an international journal of "open
peer commentary" in the biobehavioral and cognitive sciences, published
by Cambridge University Press. For information on how to serve as a
commentator or to nominate qualified professionals in these fields as
commentators, please send email to:         harnad at mind.princeton.edu
or write to:          BBS, 20 Nassau Street, #240, Princeton NJ 08542
                                                  [tel: 609-921-7771]

Strategies for the Control of Voluntary Movements with One Degree of Freedom

Gerald L. Gottlieb (Physiology, Rush Medical Center),
Daniel M. Corcos (Physical Education, U. Illinois, Chicago),
Gyan C. Agarwal (Electr. Engineering & Computer Science, U. Illinois, Chicago)

A theory is presented to explain how people's accurate single-joint
movements are controlled. The theory applies to movements across
different distances, with different inertial loads, toward targets of
different widths over a wide range of experimentally manipulated
velocities. The theory is based on three propositions:
(1) Movements are planned according to "strategies," of which there are at
least two: a speed-insensitive (SI) and a speed-sensitive (SS) strategy.
(2) These strategies can be equated with sets of rules for performing
diverse movement tasks. The choice between (SI) and (SS) depends on
whether movement speed and/or movement time (and hence appropriate
muscle forces) must be constrained to meet task requirements.
(3) The electromyogram can be interpreted as a low-pass filtered
version of the controlling signal to motoneuron pools. This
controlling signal can be modelled as a rectangular excitation pulse
in which modulation occurs in either pulse amplitude or pulse width.
Movements with different distances and loads are controlled by the SI
strategy, which modulates pulse width. Movements in which speed must
be explicitly regulated are controlled by the SS strategy, which
modulates pulse amplitude. The distinction between the two movement
strategies reconciles many apparent conflicts in the motor control literature.