[From Rick Marken (2011.10.26.1010)]
Bill Powers to all CSGers and friends.
Have a look at Nature for 20 Oct 2011, Volume 478, page 387. There you will
find an article titled "Primary motor cortex underlies multi-joint
integration for fast feedback control." The abstract concludes, "... this
provides neurophysiological support for influential theories positing that
voluntary movement is generated by the intelligent manipulation of sensory
feedback." You might incorrectly think that among these influential theories
proposing that behavior is a process of controlling sensory feedback
(perceptions) might be found a reference to Perceptual Control Theory and
some of the modeling work that has come out of it.
The word "intelligent" would have been a tip off to me that these
people don't know what they are talking about. I would never think of
PCT as about "intelligent manipulation of sensory feedback"; it's
about control of perception. As far as "influential theories" this
looks like just a blatant self-advertisement by Mr Scott. Based on teh
reference he is only referring to one theory -- the "optimal feedback
control" theory (Todorov, E. & Jordan, M. I. Optimal feedback control
as a theory of motor coordination. Nature Neurosci. 5, 1226ï¿½1235
(2002)) and the only one influenced by it seems to be Scott himself
(Scott, S. H. Optimal feedback control and the neural basis of
volitional motor control. Nature Rev. Neurosci. 5, 532ï¿½546 (2004)).
The fact that the theory is called "optical feedback control" suggests
a computational model of control that is organized around producing
clever input manipulation schemes" rather than being organized around
the control of a hierarchy of different types of perceptual variables
(as in PCT). The "optimality" of PCT comes from the type of feedback
(perceptual variables) controlled, not from how it controls them.
But I would like to see what this "optimal feedback control" model
actually is so if someone could post the Scott (2004) or the Todorov &
Jordan (2002) papers that would be great. I have a strong hunch that
"optimal feedback control" is a computed output model disguised
(somewhat) as a control of input model. But we shall see.
You might be even more inclined to expect such a reference, still
incorrectly, when of the first two authors, said to have contributed equally
to this work, one is Isaac Kurtzer of Queens University, Kingston, Ontario.
The same Isaac Kurtzer was a student of Tom Bourbon's (a cofounder of the
Control Systems Group) at Stephen F. Austin State University at
Naucogdoches, Texas, and a member of the CSG from shortly after it was
formed, an association which continued through the years at Brandeis
University where he got his PhD, just before he moved to Queen's University.
He attended many CSG meetings and was surely acquainted with all my writings
and models except perhaps those in the latest book, Living Control Systems
Isaac (like Tom) went his own way back at the end of the 1990s. Isaac
has done rather well for himself career wise, apparently. Part of his
success seems to have come from his complete desertion of PCT (to the
extent that he was ever "in it"). I think Isaac has bought completely
into what is basically the conventional "control of output" model of
the nervous system; he knows which side his career bread is buttered
on. I think you can get an idea of where he now stands from the title
of one of his referenced papers:
Kurtzer, I. L., Pruszynski, J. A.& Scott, S. H. Long-latency reflexes
of the human arm
reflect an internal model of limb dynamics. Curr. Biol. 18, 449ï¿½453 (2008).
"Internal model of limb dynamics"? Sorry, not according to PCT. I
guess he was sleeping during those parts of the meetings;-)
Of course it may be the case that Isaac has concluded that PCT is an
incorrect theory and that the models of multi-joint behavior that have come
out of it are flawed.
I think Isaac concluded that PCT was not a good career move.
If that is what he concluded, however, that is what he
should say, because PCT has been established well enough to be at least
worthy of consideration if not belief, and should not simply be ignored. If,
on the other hand, he attempted to persuade his co-authors that PCT should
be considered but was unable to do so, his coauthors at least, by scientific
morality, should have declared their reasons for not considering it
important. Or so it seems to me.
If anyone who reads this article sees the same parallels with PCT that I
see, and thinks that letters of protest are at all useful, I hope the result
will be a few letters to the editors of Nature, or perhaps some posts to the
email address given as the appropriate point of contact with the authors:
I would be happy to write a letter but only after I've managed to
understand what the hell the article shows. Maybe you could help me
out here; what is it about the experimental results described here
that has parallels to PCT, other than some of the wording (like the
stuff about manipulating sensory feedback). I really don't see why,
based on their recordings from "shoulder-like neurons in M1" they
conclude that maintaining limb position (which is I think what they
are taking about) involves manipulation of sensory input. I guess I'm
just physiologically challenged;-)
I have copied this post to that address.
Best to all,
Richard S. Marken PhD