[from Gary Cziko 921205.1800 GMT]
Rick Marken (921204.1800) reminded me to:
Read my algebra. The perception is no more disturbed by the addition of
the disturbance than it is when the reference level varies. The error
signal, however, is disturbed -- it DOES NOT go to zero -- it goes to
e + de. The error signal varies (mainly) as de. Adding dp to the perception
in the same way DOES NOT result in p equalling p + dp. So p is controlled
relative to r (or r + de) but e is NOT CONTROLLED-- it is not maintained
against disturbance at some reference level -- the purported reference
being zero.
Yes, I should have read your algebra more carefully. It says, in effect,
that there is no way for the control system to "know" if a disturbance to
the error signal is in fact a disturbance to the error signal or a
"legitimate" change in the reference level. In other words, disturbances
to the error signal are not resisted, but are rather complied with. Now I
am having trouble figuring out what led to think otherwise. Looking at the
canonical control system diagram actually made it clearer than the algebra.
Isn't it interesting, however, that all this discussion about what is
controlled did not involve any difference of opinion concerning the control
model itself? Everyone agreed that the arrow and boxes and functions were
OK. And yet there was lot of discussion concerning the use of WORDS to
describe what was going on. This is interesting since suggests that even
if we have an explicit and useful mathematical model of a phenomenon,
people still want to be able to understand things using WORDS. Agreeing on
the math does not seem to be enough. We seem want to find agreement on the
words as well, even though the words can never be as explicit as the formal
mathematical model. As Bruce Nevin has often reminded us, we gotta use
words to talk to each other.--Gary
···
------------------------------------------------------------------
Gary A. Cziko Telephone: 217.333.8527
Educational Psychology FAX: 217.244.7620
University of Illinois E-mail: g-cziko@uiuc.edu
1310 S. Sixth Street Radio: N9MJZ
210 Education Building
Champaign, Illinois 61820-6990
USA
------------------------------------------------------------------