[Martin Taylor 950525 11:00]
Bill Powers (950525.0530 MDT)
We can now see that the primary effect of Hans' model is to enable the
controlling system to continue the same pattern of output variations in
the absence of direct sensory feedback from the real controlled
variable. The same result can, I believe, be achieved by a hierarchical
control system.
I have a conjecture, about which I have asked several control engineers
without getting a solid answer:
For any single-level control system, no matter how complex, there is a
hierarchical control system made of simple scalar (PCT-standard) elementary
control systems that behaves the same way as the single-level control
system, and vice-versa.
This is pure conjecture, so far. Nobody has said that they can show it to
be false or that they can show it to be true. What it means, if true, is
that statements such as "it's not predicting; the effect can be due to
changes in a reference signal from higher levels" are untestable. In the
current discussion, it would mean that the Kalman filter effect might be
obtained equally by reorganization of a structure of simple ECSs.
I have no idea how to test the conjecture, except by counterexample, and
I cannot conceive of a counter-example. But perhaps one of the control
system engineers (active or lurking) on CSG-L might be able to make a
definitive statement on the question.
If it is true, then the important thing is what Bill says:
>It is one thing to design an adaptive control system; it is another to
>show that it is a model of real human behavior.
If both kinds of control system turn out to produce indistinguishable
results, the test (from a PCT viewpoint) is whether their structures can
be discovered in the living thing.
···
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Martin Taylor (950524 14:00) --
The skilled hunter catches fish. I claim that in doing so he is
controlling his perceptions. If I understood Rick's earlier
comment on Hans' posting, Rick would say that if the hunter hits
the fish with the spear, he is demonstrably NOT controlling his
perceptions, but is instead controlling an outer-world variable.He's not controlling the perception you're thinking of, but he's
controlling a perception nonetheless. The perception is "such-and-such
an angle relative to the direction of the fish."
He's controlling many perceptions, and at one level you are no doubt correct.
But just as you have the feeling of "being at the tip" when you feel around
blind with a rod, you also have a feeling of seeing "where the thing is"
when you are practiced in a distorting environment such as through a water
surface. There's no feeling of correcting for the distortion. You just
see it (at least that's the subjective impression). And this sense seems
to map into the words that Hans wrote about what his Kalman filter control
system does (since I can't run it, I can't comment on what it actually does).
Neither the fisher
nor the hunter is capable of aiming at where the fish "actually is" or
where the bird "is going to be."
No, of course not. That's why I suggested to Rick that he should not
despair of PCT if Hans happened to be right. Rick seemed to suggest that
the implication of the model was that the hunter could aim at where it
"actually is."
The controlled perception is an aiming
direction that is in a learned relationship to the perceived direction
of the target.
Like any controlled perception at a level above sensory intensities. The
fact that it is learned does not make it any less a perception. The way
you write it makes it seem like a modification of the output function (which
could be the case, even if it doesn't feel like it when one is in that
situation).
Martin