[From Rick Marken (930112.0800)]
Avery.Andrews (930111.1905) --
I came across the claim that feedback is to slow to solve inverse
kinematic & dynamic problems for fast movements. Where can I read about
why this claim is false or irrelevant
I think Bill Powers posted a wonderful exposition on the "feedback is too
slow"
nonsense. I don't have it available but maybe someone could re-post it; it was
really
excellent. The answer to the above claim is simply "how do you know that
people solve inverse kinematics to make movements of ANY kind -- slow or fast;
maybe they just control their perception"?
This paper also cites some
very suspect-looking work by Kelso and others that is supposed to
support a concept of `coordinative structures'
Welcome to the wonderful world of high powered motor control nonsense.
Two papers in "Mind readings" are attempts to show, experimentally, that
the leap into 'coordinative structure' models may have been a bit
precipitious.
I guess the obvious question to ask about any movements that do look
too fast for feedback is how they go under novel or unpredictable
dynamic conditions. E.g. how does the concert pianist make out with
lead weights attached to her fingers.
You've got it! The question has been asked, and answered, by PCT research
and models, many times. But no one pays attention because they already
KNOW that PCT can't work (because feedback is too slow). If you want
to read more amusing statements about feedback being "too slow" made by
authoritative leaders in the study of human movement control , try the article
by
Abbs and Winstein in M. Jeannerod (ED) Attention and Performance XIII,
Hilldale, Erlbaum, 1990 (I just pulled this off the shelf and found the
reference
by looking in the index under "feedback"). I find that the latest collection
of papers
on motor control is as good for a laugh (or better) than a Robert Benchley
collection.
The best thing about it is that these people (the motor controllers; not
Benchley) are
SERIOUS.
Greg Williams (930112) --
I was claiming that what they [nonPCTers] DO generally do is
not always based on the idea that inputs can NEVER be affected by outputs.
I agree that they do recognize (verbally) that there are feedback effects of
outputs
on inputs (Howard Rachlin comes to mind as being particularly explicit about
this).
But they don't GET (I think they just REFUSE to get) what this means -- it
means that organisms are controllers -- not controlled. I still maintain that
what
they DO (in terms of research and their analysis thereof) is done AS THOUGH
responses are caused (guided, shaped, constrained, whatever you want to
called it) by sensory inputs. So they can talk about feedback all they want;
recognize its existence and put the word in the titles of there book; they
still
clearly act as though they have no idea what the existence of continuous
feedback effects of actions on the sensory "cause" of those actions means --
it means
that the organism is controlling a sensory variable; so that sensory variable
cannot
be treated as the cause of responses -- because it is part of this loop. If
they
understood this, they would realize that their research is telling them next
to
NOTHING about what the organism is DOING; that it is controlling some sensory
variable.
Even my 10-year-old son is brighter than some PCTers have painted the
intelligence of the behaviorists;
This is NOT a matter of intelligence at all; no one is saying (I'm certainly
not)
that Behaviorists are stupid for not realizing the implications of feedback
effects. Heck, I think they are as smart as can be -- they realize the
implications of this fact and they are not interested in tossing away their
careers;
because they will be doing so if they recognize the implications of feedback
and
their colleagues DON'T.
Evan knows that if there is a feedback
connection through the computer in a tracking experiment, then that condition
needs to be recognized. I claim that behaviorists actually realize that too.
The FACT of a feedback connection is accepted by them.
Yes, indeed. And it is even taken into account quantitatively in studies of
tracking
behavior (done by non-PCTers). Yet, even though they have recognized the
FACT of feedback (just like Evan), they are still able to do experiments on
the effect of "error" inputs on responses. The point is -- recognizing the
FACT
of feedback is not enough; you've got to realize what that means (in terms of
the nature of behavior and how you would go about studying behavior based
on that realization); I say that nonPCTers are simply NOT willing to
understand
the implications of feedback (it means that organisms control, and are not
controlled by, sensory experience) and, thus, see absolutely no reason to
do research based on this understanding (testing for controlled variables).
NonPCTers have SAID many things that sound like they are compatible with
some of the realities pointed to by PCT (like feedback); but, then, genesis
says
a lot of things that sound compatible with evolutionary biology. When it comes
to TALK, it is difficult to be COMPLETELY wrong; that's what's so nice about
modelling. With a model, you finally get to the point where you just shut up
and
watch -- Zen science?
Best
Rick