EDITORIAL
Motor Control, 1997, 1, 205-207
O 1997 Human Kinetics Publishers, Inc
The Answer May Be 42:
So, What i s the Question?
Among the most actively discussed general questions in the motor control
literature are the following: Which principles underlie the control of a voluntary
movement? How are movement synergies organized? How are redundant degrees
of freedom mastered? What are the order
(collective variables) that
describe motor coordination? How are the processes of action and perception related to each other? What happens with all of the above during the processes of
development (aging, neurological disorder, specialized training, rehabilitation)?A
number of answers have been suggested based on different approaches including
experimental neurophysiology, optimization, control theory, dynamical systems,
cybernetics, and neural nets, to name just a few. The purpose of this editorial is not
to assess the relative success of different approaches to the above-mentioned questions but rather to suggest that the questions have never been formulated properly.
Thus, what are we actually pursuing when we try to answer them? Are the answers
likely to be as important as "42," the famous answer to the Big Question of Life,
the Universe, and Everything?
Let us face the fact that the main difficulty in dealing with most biological
problems, including those related to control of voluntary movements, is not in
finding correct answers but in formulating appropriate questions. To do this, one
needs to develop a set of notions adequate to describe the phenomena under consideration. Bernstein, Gelfand, Tsetlin, and their colleagues emphasized this point
in the 1960s (Bassin, Bernstein, & L.P. Latash, 1966; Gelfand & Tsetlin, 1966)
and suggested that biological problems could not be adequately formulated using
notions and ideas borrowed from other fields of science, even such well-developed
fields as mathematics and physics. Recently, Gelfand restated the problem and
introduced the notion of an "adequate language" as a prerequisite for progress in
any field (Gelfand, 1989).According to this view, formulations of biological problems must come from inside biology; then, progress in other sciences can be used
to develop the area and search for answers. This warning has been largely ignored,
and presently, formulations of problems within the field of motor control are commonly based on ideas directly borrowed from such fields as cybernetics and control theory (the motor programming approach) and a particular subfield of the
theory of nonlinear differential equations coupled with physics of open systems
(the dynamical systems approach).
The questions mentioned in the first paragraph are all nonscientific because
they contain many poorly defined or undefined words, for example, control, coordination, degree of freedom, synergy, and even what, how, and which. Even the
famous Bernstein problem (How are redundant degrees of freedom eliminated
during voluntary movements?) suffers from the same shortcoming. For example,
in order to define degree of freedom, one needs to know which variables are adequate to describe the functioning of the system under consideration. The fact that
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our laboratories are equipped with goniometers, accelerometers, strain gauges,
electromyographs, and methods of inverse dynamics does not by itself mean that
the system which produces voluntary movements can be adequately described
with a set of variables that are measured or calculated using these wonderful tools.
So, what is a degree of freedom for the system of motor control? To answer
this question, we need to knowlguess what variables are specific to the system of
movement production, the variables that make this system different from other
systems able to move. Until these variables are discovered, all attempts at solving
the Bemstein problem (as well as other problems) are likely to be unproductive.
For example, imagine that as a result of an intervention (e.g., a training protocol or
a surgery), the movement amplitude of a joint involved in a multijoint movement
decreases below the lowest level detectable by the goniometer, or the trajectories
of two joints start to show a high correlation. Does this mean that the number of
degrees of freedom in the system dropped? Certainly not! An inadequately formulated question cannot be adequately answered.
We know that the way we move is qualitatively different from the way artificial devices (from self-propelled vacuum cleaners to automobiles to the most
sophisticated robots) move. This difference is obvious when you watch Woody
Allen as a robot and as a human being in The Sleeper. On the other hand, there is a
qualitative similarity of movements among living beings, within certain, wide
ranges. This similarity suggests that there must be important, basic commonalities
in the organization of the system for movement production across species, specific
for movements of living systems.
Let us also have the courage to identify explicitly the system of interest,
separate it from other systems within the body and from external systems, and say
with respect to certain groups of questions: This is beyond our comprehension.
This statement does not mean that we are turning agnostic; rather, it shows that we
understand our task not as trying to create a General Theory of Everything but as a
search for a set of adequate notions for a precisely defined system within our bodies.
N.A. Bemstein liked to tell the following story (as recollected by Prof. V.M.
Zatsiorsky):
You probably do not know that God has a cousin who has never been very
famous. So, the cousin asked God to help him achieve fame and glory in
science. To please the cousin, God gave him the ability to obtain any information about physical systems in no time and to travel anywhere within a
microsecond. First, the cousin decided to check whether there was life on
other planets. No problem; he traveled to all the planets simultaneously and
got an answer. Then he decided to find out what was the foundation of matter. Again, this was easy; he became extremely small, got inside the elementary particles, looked around, and found an answer. Then, he decided to learn
how the human central nervous system controls movements. He acquired
the information about all the neurons and their connections, sat at his desk,
and looked at the printout. If the story has it right, he is still sitting there and
staring at the map of neuronal connections.
Before our minds are buried under heaps of data, shall we focus on formulating the questions properly?
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Respectfully,
Mark Latash. Editor
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207
References
Bassin, P.V., Bernstein, N.A., & Latash, L.P. (1966). Towards the problem of the relations
between brain architecture and functions in its modem understanding. In Physiology
in clinical practice (pp. 3849). Moscow: Nauka. (In Russian)
Gelfand, I.M., & Tsetlin, M.L. (1966). On mathematical modeling of the mechanisms of the
central nervous system. In I.M. Gelfand, V.S. Gurfinkel, S.V. Fomin, & M.L. Tsetlin
(Eds.), Models of the structural-functional organization of certain biological systems (pp. 9-26). Moscow: Nauka. (In Russian; translation available in 1971 edition
by MIT Press, Cambridge, MA)
Gelfand, I.M. (1989, November). Two archetypes in the psychology of man. Unpublished
lecture, Kyoto prize acceptance speech, Kyoto, Japan.
Acknowledgment
I am very grateful to Prof. V.M. Zatsiorsky for permission to publish his account of
the story about God's cousin.