[From Rick Marken (940225.0900)]
Bill Powers (940224.0915 MST) --
All this leads to my "universal error curve," shown below:
I set up a quick demo comparing control systems with "normal",
"saturating" and "universal" error curves. The "universal" curve
works exactly as advertised -- when a disturbance pushes the
perception far enough away from the reference the control system
just gives up; a control system with a saturating error curve and
an integrated output keeps at it -- and eventually regains control.
I like this universal error curve; I think it might be able to
capture what happens in my conflict studies. It might account for
the fact that the subject (unlike the plain vanilla control model)
stops trying when the net disturbance to a controlled variable cannot
be compensated by the output. I will try to do some tests of the
"universal error curve" in the context of my conflict studies.
The "universal error curve" is a rather appealing way to account for
a phenomenon that has always puzzled me (from a PCT perspective) -- and
that you mentioned in your post -- the fact that perceptions seem to
"capture" control efforts under certain circumstances. This used to
happen to me all the time (before I was married); I would be happily single
when suddently a young lady would walk by and suddently I had to get to know
her (control various perceptions related to her -- I leave it to all the
lurid minds out there to guess which perceptions those might have been) . I
think it's this "capture" phenomenon" that is the heart of "abstinence"
approaches to eliminating "bad habits" (in PCT a "bad habit" would be
controlling that has reliable unwanted side effects) -- and these approaches
seem to work. I'm thinking of things like AA, cathlolic (unisex) schools, etc
which aim to take people away from the "offensive stimuli". The "universal
error curve" suggests that what is actually happening is that these methods
keep people away from disturbances that would "reduce" their error enough to
"switch on" those always present "bad habit" control systems.
Cliff Joslyn (940224.1400) --
It looks like you are more interested in a legal deposition than
a substantive discussion of models. Tom and Mary's descriptions
of "systems science" capture in eloquent detail my own impression
of the field. If "system's theorists" want to do PCT then they
are free to do it. If we find anything of in systems science that
helps us study or model purposive behave, then we will feel free to
if there are any ST people who are "doing anything related to understanding
the nature of living systems" then theyare by definition doing PCT, EVEN IF
THEY DON'T KNOW IT or acknowledge it as they should.
How could this be?
Easily. The idea is that (1) an ST person considers the operation of living
systems; (2) (s)he considers that feedback may be important; (3) (s)he then
uses feedback to describe some interesting result. Bingo.
I don't know what to say, Cliff. You've been on this net for a long time.
You must know that there are many psychologists who are intersted in "the
operation of living systems" and think "feedback may be important" and
use "feedback to describe some interesting result". But, bingo, they are not
even close to doing PCT. These psychologists don't understand control, don't
build working models, don't test for controlled variables, don't study
individual's but, instead, use feedback to describe average results over
many subjects, take input- output relationships at face value -- in other
words, they are not doing PCT at all. People are NOT "doing PCT" just
because they use words like "feedback", "living systems" and "control theory"
is an enormous misapprehension. The fact that you believe that that ARE
doing PCT - - after this much time on the net -- is a testament to the power
of perceptual control (and more than a tad depressing).
Bill Leach (940223.18:51 EST) --
I don't personally believe that the term "feedback" has any place in PCT
unless there is an actual situation where it is determined that a portion
of the output signal is returned to the input to enhance control.
I see that you come to PCT via engineering control theory. I hate to
say it but this does not bode (no pun intended) well; control engineers
(on this list, anyway) have been quite reluctant to abandon some of their
well-entrenched ways of looking a control systems -- making it impossible
for them to learn PCT. The control theory of PCT is identical to the control
theory of engineering; what is differentis the mapping of control functions
to system functions, a process that often makes explicit some functions that
engineers take for granted (and, thus, ignore). Bill Powers described the
difference between the engineering and PCT mapping of control theory to actual
systems in a wonderful post several months ago. Perhaps someone can
find it -- it may have already appeared in a closed loop.
I will just say here that the difference between the engineering and PCT
mapping of control theory to systems is most profound in the part of the
control loop where (as you say) "a portion of the output signal is returned
to the input". In engineering diagrams (the maps of the system used
by engineers) this "output takeoff" is, indeed, just a line
connecting the output back to the comparator. This line looks like a
wire (and in some control systems it may be) but in a living control
system this line is a neuron carrying a perceptual signal. The
place where this line connects to the "output" variable is a LOT
more complex than the engineering drawing lets on because this is
the place where the "output" variable is sensed. The sensor is the
perceptual function in PCT and in living organisms it is the
afferent nervous system -- which provides us with our perceptions
of the world. The "output" variable in the engineering drawing is really an
environmental variable that is sensed by the organism. In PCT we call this
"output" variable a controlled (environmental) variable. The actual "outputs"
of an organism (according to PCT) are the physical actions that affect the
state of the "output" (controlled) variable; in engineering drawings,
the PCT output variable is called the "plant output".
In PCT, the relationship between action and result (between plant and
"output takeoff" in the engineering model) is the feedback function;
it is the set of physical laws that determines how actions affect the
controlled perceptual consequences of those actions. (The PCT model
makes it explicit that the perceptual variable is controlled; this,
of course, is also true in the engineering model -- it's the same
model -- but the engineer would say that it is the "output" -- really
the "output takeoff" -- that is controlled). The relationship between
action and perception (in a living control systems) is called feedback
because the the effect of these actions are fed back onto the actions
themselves (because they occur in a loop). In PCT, "feedback" is a
FUNCTIONAL DEPENDENCE of variables on themselves -- it is not a
THING that can be GIVEN. Feedback is the central concept of PCT:
because of the functional dependence of actions on themselves ("feedback")
we are dealing with systems that have completely difference behavioral
characteristics than systems that do not have it. When the sense of
the feedback is negative (actions have effects that reduce their own tendency
to occur) the behavior of a feedback system is PURPOSEFUL -- it maintains
perceptual variables at internally specified values.
Bill Powers (940224.1730 MST) to Martin Taylor (930424.1140) --
A wonderful post on categorical perception, Bill.
At the stage in which our model- building exists now, I see no merit in
trying to add complexities to it. Rather, we should be trying to boil it
down to the simplest form possible that still covers the main phenomena.
I second that emotion.