[From Rick Marken (930919.2100)]
Dag Forssell (930918 0025) says:
That is not the way I read you. You also said:
in a good control system the size of the variations of p around
r be so small that they are undetectable by the instruments used
to measure p.
So Michael was talking about a bad control system. I certainly read
your statement as a rejection of Michael's observation.
Sorry. Poor writing on my part. I should have said "high gain"
instead of "good".
I said (to Michael) --
Your statement above suggests that you believe that the dynamic
deviations of p from the reference level, r, are what drive
(cause?) the outputs of the control system. That is, dynamic
(temporal) variations in (r-p) are the cause of the temporal
variations in the outputs that affect p, keeping p near r. Is
this what you think is going on in a control loop?
Dag says:
A good interpretation of Michael and an innocent question. You
proceeded to argue against it, without any qualifying transition,
which I interpreted as you saying that Michael is a half-baked
idiot for thinking so. This created a large disturbance in me.
Your clarification does nothing to change my impression.
Apparently it was a disturbance to many perceptions -- including
Bill's -- so you are in good company. There's not much I can do
about your interpretation of my post (it's yours). All I can do
is assure you (and Michael and everyone else who might care)
that I am not in an intellectual sparring match; I'm not trying to
prove that I am smart and everyone else is an idiot. I am sure
everyone on this net is a lot smarter than I am. There are one
or two things that I think I understand -- so they are very
precious to me. But if it turns out that I am wrong about them
(or anything else) then that will be fine and I will have learned
something. The net, for me, is about batting around ideas -- NOT
winning the battle for smartest person (I already concede defeat).
I'm sensative about this because I know how unpleasant such
substanceless, intellectual sparring matches -- aimed only at
improving one's own imtellectual image by verbally humiliating
your opponent (a la W. F Buckley) -- can be. For me, it's the ideas
that are important -- not showing that "I know X, you don't so you're
stupid".
I am prepared to be shown that I have said something wrong. I'm
trying to learn stuff too. If I'm shown that I'm wrong about
something then this is a learning experience. I'm sure that
much of what I say is wrong -- I'm not speaking ex cathedra
here . Nor is discussion on this net an ego trip (for me,
anyway) -- it's a learning experience. I enjoy the ideas and I
think they're important. If someone says something that
conflicts with my understanding (meager as it is) of PCT then
I will call them on it -- knowing that I might be wrong. I have
been wrong plenty, I accept it when someone explains how I
am wrong (as I did fairly recently when Bill P. pointed out
that one of my efforts at a mathematical proof of some concept
was a hash).
I participate on this net because 1) I want to communicate what
I know (or think I know) about PCT with those who are interested
2) I want to learn from those who know things I don't know and
3) I want to work towards a better understanding of organisms as
perceptual control systems. If someone says something that seems
wrong to me, I feel free to say so -- and try to explain what seems
wrong about it. I expect people to call me on it when I say something
that seems wrong (and they do call me -- and when they do I don't feel
like they are saying that I'm stupid -- even if they are).
Remember, when I say something like "That's wrong" I am not saying
"you're stupid and I'm smart" or "I'm better than you" or "even
a 2 year old could understand this" or anything else that has to do
with intellectual competition. I'm just trying to get the PCT
perspective on living systems right.
So with that apologia out of the way, let's see what (I think) is
going on with a control systems.
Dag says:
Would you please clarify what you have typed above. Is perceptual
input equivalent to the error signal e = r-p?
I have been somewhat ambiguous, I'm afraid. In manual
control the input to the control system is error (r-p) where
r and p (and e) are considered to be variables in the environment.
In PCT we are very clear about the fact that r and p are
inside the person and r is only manipulable by the person.
But in my development of the behavioral illusion the location
and value of r and p are irrelevant. From now on let's assume
that the input to the system is p, that r is zero and that the
comparator is just an inverter -- so e=-p (which is equivalent
to your equation with r=0). The reason is that the behavioral
illusion does not depend on the location or value of r; it depends
on the fact that organisms are in a negative feedback realtionship
with their environment. As Bill P. said in the Psych Review (1978)
paper, the behavioral illusion occurs because organisms are N -
systems (systems in a negative feedback relationship with their
environment) not Z-systems (open loop systems -- zero feedback
relationship with their environment) or P-systems (positive
feedback relationship).
You say:
The temporal deviations of p from
r create an error signal e, which _contains information_ used by
the output function (again, see video script p. 11).
I said:
This part is basically true
You say:
So the only thing Michael said is true. But in a loop it loses its
validity? I don't think so.
I was responding to the fact that what Michael said could be
understood (by me anyway) in wo ways: 1) as a description of a sequential
input-output view of how control works (the "Plans and Structure
of Behavior" approach to describing control) or 2) as a description
of the relationships in a control loop. The first meaning (which
might not have been Michael's -- that's why I asked) causes
problems for me becuase it is at the heart of psychology's failure
to understand the nature of control. It implies a sequential state
analysis of the behavior of a control system -- which leads to the
wrong results.
I am aware of the behavioral illusion. I have always thought that
the illusion is to think that there is a direct causal relationship
between input p and output o (ignoring r).
No. The illusion is that that observed relationships between
stimulus variables (d) and output variables (o) in N- systems reflect
characteristics of the organism; in fact, they reflect characteristics
of the feedback function (not a part of the organism) that relates
o to p). Experiment 4 on pp 156 -159 of LCS I is a good
demonstration of the behavioral illusion; note especially fig. 6 on
page 157. This is a plot of the relationship between d and o in a
tracking task; this is an input -- output plot; it would be reasonable
to assume that the nature of this relationship (cubic) depends on
charateristics of the subject; in fact, it depends entirely on the nature
of the environmental function connecting output to perceptual input.
This is a stunning demonstration because it really pulls the main
support away from the foundation of scientific psychology.
I think that it is VERY important (for psychologists, anyway) to
understand what is going on there. You can demonstrate it to
yourself with rubber bands, if you like. Do the rubber band demo
twice, once with a very tight and once with a very loose rubber band
connecting the subject to the knot. In the first case, you will see
that the subject makes very small finger movements per unit movement
of your finger. In the second case, the subject makes very large
movements for the same unit movements of your rubber band. It
looks like the subject has become more sensative in the second case;
reacting much more to the same disturbance that produced almost
no reaction the first time. But there is no change in the subject; just
in the enviromental connection from subject to controlled variable.
A psychologist who didn't know that the subject was controlling the
knot (and doing whatever was necessary to keep it at the reference)
might conclude that the subject is more sensative to certain kinds of
rubber bands than to others. THAT'S the behavioral illusion.
I was discussing a version of the illusion where one measures
the relationship between -p and o instead of between d and o. The
illusion still occurs (the observed relationship between -p and o is
not what is expected based on knowledge of the real function
relating p to o) but I suppose I am wrong to call it the behavioral
illusion because it could only be measured neurophysiologically;
so maybe I should call it the neurological illusion.
Have you perceived that
this is what Michael and I mean when we write about a direct
causal relationship between the error signal r-p and output o?
No, because my point had nothing to do with r (that's why I
included it in the input, as r-p). I think you didn't understand
what I meant by "behavioral illusion" (but I still think that
you're smarter than I am).
If by output you mean the momentary muscle contractions and
therefore hand acceleration, I think Michael's and my notion of a
direct causal relationship between r-p and o holds very well
indeed.
Agreed. But remember, in my question I asked if what was
being caused were "the outputs that affect p, keeping p near r".
The derivative of o (in the model) is not what keeps p near r; it
is what is caused, but it is the current value of the integral
that is the effective output. The integral is what preserves the
effects of all variables around the loop -- and makes it so that
the derivative that is "caused" at any instant happens to be
the "right" one -- ie. the one that has the effect on p which,
in the context of the current environmental circumstance, moves
p toward r.
I think most people would intuitively think that their output is
their muscle contraction -- the way they try to move the hand.
I think the output that matters is the one that influences the
variable under control.
Please run your hypercard again and confirm my expectation
that r-p is linearly related to the derivative of o, o'.
You clever devil. I did it before you asked and your prediction
was confirmed; the derivative is linearly related to p (or r-p with
r=0). But the derivative is not what produces control of p. If you
just add the derivative of o (instead of o) to p each time you get
no control.
I agree completely, o versus p is the basis for the behavioral
illusion. And the integration is not the issue you make it.
Correlation of r-p with o is not an issue that is central to the
behavioral illusion. More than that: It has nothing to do with it.
In the rubber band version of the behavioral illusion that I
suggested there is no change in r (the reference position of
the knot) and yet the illusion occurs; it is an especially
impressive illusion if all you can see is d and o -- not the
the controlled variable OR the feedback function (the rubber
bands that connect subject to knot). If we could dip into the
brain and measure variations in p (with r = 0) and
o (finger position) in the same experiment (with changed
feedback function rubber bands) we would get the same
apparent change in the relationship between p and o.
Of course, if you knew that the relationship between p and
o was likely to be misleading, you might look for ways to
transform o so that you linearized the relationship; however,
taking the derivative only linearizes if the output function is a
pure integrator.
You said:
Please consider applying your understanding of PCT and reconsider
your reply to Michael.
This is not a religion group. I don't want to feel like I have to
tip toe around, worrying about whether I am treading on some sacred
beliefs. I will TRY to be more polite -- I'm REALLY not trying
to be mean -- but I think it MUST be OK to suggest that someone
MIGHT have an incorrect notion about PCT (heck, people say I
don't know what I'm talking about and nobody jumps in to say "take
back what you said to Rick"). If I say some idea might be wrong ( or
if someone says something about PCT is wrong) then that should be fine,
ESPECIALLY if people take the trouble to try to show --mathematically,
experimentally or computationally-- why it's wrong. I have no
problem with people saying PCT is wrong; in fact, I wish
people would say it and then show how it's wrong -- not just
in words ("I don't like it because...") but by test ("if you measure
this variable while manipulating that one you find this instead
of what PCT says you would find") . Now THAT would be re-
freshing. But even verbal disputes are helpful because they
help us find ways to clarify what we are trying to say. If people
are personally offended when someone says "that's wrong" then I think
they are looking at this debate thing from the wrong level of their
own perceptual control hierarchy -- in my humble opinion.
Are you less surprised now?
No.
I think it is highly worth while to
clarify the behavioral illusion. But let us be very clear about
what it is.
It sounds to me like you are saying that I should be sure that
I am right before I post anything. I can't make that guarantee.
This is not a refereed medium so a lot of mistakes will get
posted as "facts". I try to be careful but basically we're thinking
on our feet -- like at a conference. I've made mistakes, Bill's made
mistakes; everyone's made mistakes. Only religions expect (and
require) infallabilty; scientific ideas are expected to be wrong. The
hope is that some new ideas and realizatons can come from the uninhibited
discussions on this net. When we start requiring respect for ideas
(rather than people) then I'm outta here. Question ideas; love people.
Dag Forssell (930918 1125)--
You are thoroughly trained in IV-DV research and use
it below to show something that happens to be true, but has no
significance. You draw false conclusions -- unless I shall prove
mistaken,
I think my mistake was saying that this relationship was an
accurate reflection of the feedback function. This is true for
the relationship between d and o but not necessarily for that between
r-p (or -p) and o -- which is what I plotted. The relationship
I plotted is a good example of an "illusory" representation of
the real relationship between (r-p) and o -- but it's probably
not the inverse of the feedback function.
Shall we call this the CORRELATION ILLUSION?
No. Correlation is just a measure of the degree of (usually) linear
relationship between variables. I was not making inferences
about populations based on the correlation and then applying
the results of that inference to individuals -- THAT's one of
the BIG problems with using statistics in psychology (the other is
accepting a low but significant measure of correlation as reasonable
data on which to base models of individuals).
Your mistaken application of correlation analysis above, in lieu of
consideration of functional relationships, is interpreted by this
observer as an excellent illustration of Bill's thesis.
I plotted one variable against another. Where was the "mistaken
application of correlation analysis"?
It seems one is much better off without studying statistics.
I didn't report ANY statistics; a statistic is a measure of sample
characteristics -- like mean, standard deviation, r, t or F -- that
can be used to make inferences about the corresponding measure of the
population from whence the sample data were drawn). Statistics,
per se, are just fine (or do you object to RMS as a measure of
voltage)?
Standing by for your counter-blast in this exchange of
disturbances.
Boooom.
Or Beeeep. Depending on how you hear it.
Talk to you tommorrow, probably.
Love
Rick