[From Bill Powers (960622.1045 MDT)]
Chris Cherpas (960621.0946 PT) --
While the 11 levels are often intuitively appealing, I keep looking
for variables that would constrain what the next level to develop
in a developing organism would be (or better, what it _must_ be if
that's possible).
You might try just looking at your own experiences, which is what I did.
All perceptions that I would classify as configurations, for example,
seem to require the presence of, and to be composed of, sensations which
are not themselves configurations. And every sensation seems to be
composed of a collection of different intensities. Every transition is a
transition from one set of configurations, intensities, or sensations to
another set of them. To this you can add that in order to control a
higher perception, you must be able to affect and change the lower
perceptions of which it is made. So all that remains is to examine every
perception of every possible kind, and trace its lineage to other
perceptions which, presumably, are of lower order. The old Gestalt
psychologists did some of this sort of subjective analysis, although
they didn't include the idea of varying one type of perception as the
means of controlling a higher type.
This sort of analysis provides basic observational data which any
mathematical model of perception has to fit. The problem with many
models of perception is that they begin with the mathematics, which then
generates its own kind of structure without regard to the structure that
actually exists. There's a strong tendency among mathematical modelers
to look for a single unit of perceptual organization which can then just
be repeated for any number of levels. This sort of model has a certain
esthetic appeal, and of course it is much easier to produce than a model
that has to explain something different at every level. Basically you
solve one problem, and then just say "etc". However, I doubt very much
that the same operations are involved at every level of real perception,
or that nature simply says "etc."
While not sufficient to explain the development of a higher level,
controlling perceptions involving bigger bandwidth seems to be the
(at least typical) result.
Martin Taylor's reply to this idea (960621 15:30), while still
contaminated :=) by information theory, is a good one. The actual
bandwidth of higher-level systems is less than that of lower systems --
that is, the speed with which changes in the relevant variables can be
perceived or opposed is less than at lower levels. This is largely
because higher-level perceptions, by their very nature, can't exist over
short periods of time (consider "sequence"). However, because higher
systems in general use many lower systems in parallel, the mechanics of
their behavior may seem to involve higher bandwidths -- quicker
reactions to disturbances.
By positing the "system concept" level as the highest level, PCT
seems to be saying that the (cyclic or other) interactions of
functional structures represent the limit to what kinds of
perceptions we can control. But what about the process through
which these functional structures change (e.g., evolution,
learning, developing new levels in the hierarchy)?.
System concepts are only the highest level of perception I have been
able to catch myself using (and infer that others use). The fact that I
can notice them implies that there must be at least one higher level,
but since I have no place to stand from which to see it, I can't
identify it. Perhaps someone else with more levels could.
The process of change in an individual organization is subsumed under
the concept of reorganization (which see in B:CP). I don't conceive of
this as the "highest" system, because it must be fully functioning from
birth or before in order to account for the growth of the hierarchy of
control. And I don't see it as intelligent, because it must work before
the brain has any understanding of the external world or itself at any
level. I see it as a separate system, as it were off to one side of the
growing hierarchy. It is concerned only with controlling intrinsic
variables related to life support and perhaps other genetically
transmissible considerations.
···
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Martin Taylor 960621 14:30 --
RE: influence.
The "disturbing influence" in this case is then dist(t) = integral
(disturbance torques) dt,
So you see the velocity as containing two distinct components, one due
to the disturbing variables and one to the output variable. This is more
or less what I thought.
This decomposition of the velocity, however, requires perceiving at
least the output force as well as the controlled velocity, and it also
requires knowing that the velocity changes in proportion to the output
force (in a linear system). These perceptual capabilities and this
knowledge of the nature of the feedback function are not part of the
basic ECU in PCT, although in Hans Blom's model they do exist even if
they're not explicitly spelled out (they're built into the simulation
program).
So even though an external analyst who can perceive these things can
compute the missing component of the velocity, the control system, the
simple ECU, cannot. This means that the ECU itself can't distinguish the
component of the velocity _perception_ that is due to the external
disturbing variables from the component due to the output variable.
When we describe the basic principle of operation of the basic ECU, or
build one, therefore, we can't make its operation depend on being able
to separate the components of the perceptual signal. The ECU works only
with the ENTIRE perceptual signal, the unseparated sum of its conceptual
components. It subtracts the ENTIRE perceptual signal from the reference
signal; it does not subtract just the component due to independent
disturbing variables. The effects of its own ongoing actions are just as
much part of the perceptual signal as the effects of independent
disturbing variables are: those effects get subtracted, too.
In speaking of how the ECU works, we often use a simplification that
makes the description shorter. We say that the output of the system
mirrors the disturbing variables. However, this is not strictly true.
The feedback function and the disturhance function may be quite
different from each other, and nonlinear to boot. But even more
important, this mirroring must contain an offset sufficient to bring the
perception to the same level as the reference signal. In other words,
the sum of output effects and disturbance effects is not zero, but is a
magnitude of the perceptual signal that matches the (generally nonzero)
magnitude of the reference signal, as translated through the input
function. Since the reference signal is given from above independently
of the operation of the control system, we can't say that the output and
disturbance effects sum to any particular net effect. They sum to
whatever net effect is currently specified by the reference signal (with
suitable approximations noted).
So it turns out that to deduce the component of the velocity that is due
to external disturbing forces, we must know not only the form of the
feedback function and the magnitude of the output variable, but the
current setting of the reference signal as well. Obviously, the simple
ECU has none of these pieces of knowledge. And since IT can't use these
pieces of knowledge in generating its control behavior, we can't use the
same pieces of knowledge in explaining how it works. We can't say that
the fact that there is a component of the perceptual signal that is due
to an external disturbance has any role in the process of control.
This is not to say that given knowledge of the various functions and
signals, an omniscient external observer could not deduce at least the
sum of the influences (in your sense) caused by (otherwise unknown)
external disturbances. However, this does not mean that the control
system does the same thing.
One of the beauties of the basic control process is that it can work
WITHOUT this kind of elaborate analysis and decomposition of the input.
I don't doubt that the external analyst could design a control system
that does use the knowledge that the analyst has, computing the
disturbing influence, calculating the output needed to oppose that
influence, and producing the output required to make the input match a
reference value. That is essentially how Hans Blom's version of a
control system works. But this is not the elementary control unit of
PCT: it is a MUCH more elaborate kind of design which, to be built,
would require many sensors of a kind that the simple ECU does not need,
and which is capable of extremely complex mathematical operations, such
as taking the inverse of a transfer function, which are not necessary in
the PCT model. Perhaps such elaborate designs do exist somewhere in the
brain, but they are completely unnecessary for most control processes.
I understand what you're saying: that the analyst can compute the
component of the perceptual signal that represents an influence of some
external independent disturbing variables. If some way were known of
computing the information flows in a closed-loop system (and as of
today, I have seen no such computation), it would probably be possible
to state how much of the technically-defined information in the
perceptual signal, in bits or bits per second, is due to the external
disturbances at least in the aggregate. But this is only a computational
exercise if the system itself is not separating that information out and
using it as the basis for constructing its output. The analyst has a
receiver for that kind of information, but if the control system does
not, then that information is significant only to the analyst.
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James R. Nord (960622) --
Welcome aboard, James. I don't recall your letter of 23 years ago -- I
hope you'll forgive me. But I am very glad to know of your many parallel
experiences and ideas, and to welcome you to this discussion. It seems
that you have more of a running start than most people coming to PCT
have.
I have met all the cybernetics people you mention but Wiener, Ashby, and
Gray Walters. In fact, throughout the development of PCT both before and
after my book, I tried many times to get the model across, attending
meetings of the ASC and often receiving what seemed to be strong
support. But in fact, the CSG was formed at an annual ASC meeting in
Philadephia -- largely in response to the total lack of interest shown
in our presentations. PCT was seen as both competition and an
implication that there was something that the gods of cybernetics may
not have understood -- neither implication being welcome.
The basic problem was always that cyberneticists operated several levels
of philosophical abstraction above the level where PCT exists. Very few
of them had anything but a layman's notion of what a control system is
and how it works. The general attitude I encountered was "Oh, we know
all about that servomechanism stuff; nobody does that any more." But the
truth was that hardly anybody in cybernetics after (perhaps) Wiener ever
DID do that stuff. If there were ever any technical people in the ASC,
they quickly dropped out (or submerged themselves) and the dilettantes
and nuts took over. Have you every tried to conduct a poster session
with a computer demo of control theory while a troop of people tap-
danced in the middle of the hall? I have. By the time I started
seriously trying to introduce PCT to cybernetics, I found that I spent
most of my time defending my "behaviorist" position and trying to
convince people that "hierarchy" and "control" were not propagandistic
terms from a Fascist agenda. At one Gordon Conference, I had to listen
to Heinz von Foerster sneering at hierarchical control theory by
chanting "the PUUUURpose of the PUUUURpose of the PUUUUrpose." I have
not had uniformly good experiences with the ASC and its luminaries. It's
a shame, really, because in the background on both sides there seemed to
be a willingness to reach some common ground. But too much happened to
undermine the process.
I'll let others try to answer your questions. You will find some
interest in them. And I reciprocate your appreciation -- with your
background you'll slip right into our group without a ripple. Of course
if you want to make some ripples, that's fine, too.
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Best to all,
Bill P.