Newsgroups: bit.listserv.csg-l
Date:         Fri, 4 Sep 1992 16:25:10 EDT
From:         mmt@BEN.DCIEM.DND.CA
Subject: Re: Concepts & models; Busses

[Martin Taylor 920904 15:40]
(Bill Powers 920904.1130)

Very quick, or it will be 3 weeks till I answer...

>It's not self-evident that left-over perceptions or control systems
>must have the function of "alerting." I don't dispute that there will
>be perceptions and systems not in use, because of the df problem.

Self-evident is a funny term.  It's self-evident to me, in that I can find
very little that is more "atomic" than the simple statement of the df
situation, from which the existence of alerting systems follows directly,
given the basic axiom of PCT (not Greg's 6 axioms, but the axiom that
behaviour is the control operception).

Perhaps the problem is that we have a different sense of "alerting."  The way
you use it, it sounds as if you make some connection with consciousness.
All I want to say is that the presently uncontrolled percepts are monitored,
and the consequences of this monitoring are that when something relevant
happens, control moves to percepts that are marked as possibly having become
important to control.  That means either that there were already "spare"
degrees of freedom that were not being used actively for control (I suspect
this is the normal case) or that some degrees of freedom that were being
controlled are dropped in favour of the ones that were "alerted."  I take
"alerting" to describe the marking of df as being probably useful to control,
and don't put any more on it than that.

In the diagram to which you refer. the arrows were meant to indicate this
kind of non-specific pointer function, not to specify a mechanism.  On other
occasions I have proposed gain functions with dead zones as being a way that
ECSs can perform the alerting function on themselves.  In that case, there
is no overt mechanism, but the df shift occurs as a consequence of conflict
between the "alerted" ECS and previously active ones with correlated perceptual
functions.  There are probably dozens of other possibilities that come within
my concept of the necessity of "alerting."

As a related topic, it seems to me probable that there are usually far fewer
output degreed of freedom used in active control than are available, because
the use of all available ones seems rather like a very high workload condition.
If this is so, then the activation of an output degree of freedom as a
consequence of an alerting situation need not take a degree of freedom
away from what was already being controlled.  It also implies that output
degrees of freedom may, in a way, "drift" in and out of use by the actively
controlling ECSs.  There's a difference between a cat standing guard by a
mousehole and the same cat in a similar attitude, resting.  The guarding cat
is actively controlling a lot, without moving, whereas the resting cat is not.
================

>In the CT diagram, every block and every arrow is assigned a specific
>function. By instantiating these functions it's possible to construct
>a working model of a control system. Even in cases where we can't yet
>instantiate the functions, we can see that if we could, or if we could
>fake it, we'd have a runnable model.

This is the construct I called "symbolic" PCT, and that I see as the reason
you had problems with your reorganization simulation in flipping the signs
of output-to-reference links in an active controller.  Symbolic PCT is
surely easier to program than is distributed PCT, but I doubt it is as robust
or as true to life.
================

>I can see that the variability of the perceptual signal relative to
>the reference signal would be changed by changing the loop gain,
>loosening or tightening control. But that is AFFECTING variability,
>not CONTROLLING FOR variability. In order to control for variability,
>the system that is varying the common-mode reference signal must
>perceive something about the lower system that constitutes its
>variability. What would that be?

Again musing rather than proposing...Imagine a perceptual function consiting
of a leaky integration of a rectified time-difference signal.  If I remember
my rusty electronics--


--->|--C1--------------
           |  |
           R  C2          where C2 >> C1 (I think I put the rectifier in the
           |  |            wrong place)
-----------------------

One can imagine other perceptual input functions that might do the job.  They
don't have to be complicated, and they can combine the inputs from many
lower-level ECSs, either before this circuit or after it. depending on whether
they perceive something like the variation of the average or the average
variation of a lower-level ECS.

Martin
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