IT and PCT III: Jason returns from hell

CSGnet Archive CSG1994
1

[From Rick Marken (940207.0900)]

Bill Leach (06 Feb 1994 17:09:28) --

You don't really know p(t)
in an experiment and you definately don't know what the function h()
actually is.

We don't know p(t), true. But in a tracking task, we are able to
mimic the subject's behavior pretty accuratly under the assumption
that p(t) = c(t). We don't know h() exactly either but, again, modelling
shows that we know most of the relevant aspects of h(). If we didn't
have a pretty good idea of what p(t), h( ) and g( ) were, we would
not be able to reliably build models whose behavior correlates with
real human behavior at the .99+ level.

Also, I suspect that there are unknowns concerning the control loop that
actually is used by the subject to input the "g(o)", that is the mouse
and its' related interactions with the subject.

Yes. We have to guess at the system parameter(s) and there are
uncontrollable aspects of the environment (little changes in g(o)
becuase of changes in mouse friction, etc). But these turn out to
be very inconsequential details -- as proved by the success of the
basic model in mimicing human behavior.

It seems to me that information theory can be useful to PCT for a couple
of reasons. Probably the single most important one being its' rather
rigorous analysis of information transfer mechanics.

We have been waiting breathlessly for a coherent description of how IT
might contribute to PCT. I have never doubted that it MIGHT contribute --
but so far I have seen nothing from ITers but post hoc, QUALITATATIVE
assertions about behavior that are not obviously related to Shannon's
theorms. What we have shown in the "information in perception" debate is
that the IT concept of information is definitely irrelevant to the
OPERATION of a control system; there is nothing "in" the perceptual signal
that "informs" the system about the appropriate output to generate in order
to compensate for the net distrubance to the controlled variable. Now
the ITers are saying that all they meant by "information in perception"
is that you can't solve for d in p = o+d unless you are given o and p.
I have to agree with this astounding revelation -- but I don't see how
that goes much past basic PCT, since PCT accepts the tenets of algebra.

Nevertheless, IT might be useful to an OBSERVER of a control system.
AS you say:

I would also suggest that IT might be useful in analyzing how a deviation
from expected result might be due to supplying information (the signal
generated for perception) beyond what was intended.

If you are talking about a deviation from a result expected by the
OBSERVER of a control system, then I agree -- IT MIGHT be useful in
analyzing why this occurred. A demonstration of how this analysis might
proceed would be very helpful. But we already know that IT has nothing to
contribute to our modelling of how the control system itself deals with a
"deviation from an expected result" if this means "deviation of a perception
from its reference state".

If IT showes that there is information in the signal generated for
perception that is in addition to the intended information then the
nature of such information could be useful in determining the nature of
control system changes (that is algorithmic changes).

A very big IF.

I think we have shown beyond a reasonable doubt that there is
no information for the control system about anything (other than
the state of the perceptual signal itself) in the perceptual
signal. I have no idea what the "intended information" in the
perceptual signal might be.

The bottom line here is this: PCT is about the behavior of variables
in a CLOSED LOOP; information theory is about the behavior of signals
in a commincation channel -- an OPEN LOOP. The behavior of variables
in a closed loop is compeletely different than the behavior of the same
variables when the loop is open. This is why ANY open loop - based model
is irrelevant to understanding purposeful behavior.

Best

Rick

2

<Martin Taylor 940207 19:45>

Rick Marken (940207.0900)

The bottom line here is this: PCT is about the behavior of variables
in a CLOSED LOOP; information theory is about the behavior of signals
in a commincation channel -- an OPEN LOOP.

Huh!??!?!

Haven't you read ANY of the attempts I have made at tutorials on information
theory? I may write poorly, but I can't believe I write THAT poorly.
Even if IT is often used to analyze communication channels, that
isn't what it is ABOUT unless a particular person chooses to use it for
that purpose. Is a screwdriver ABOUT building staircases? Is a paintbrush
ABOUT making rooms nice to be in?

If I remember correctly, my first naive attempt to introduce information
theory into CSG-L was based on the information stability of a closed loop,
stability implied by the fact of control. Does that sound as if information
theory demands open-loop conditions? Maybe in your imagination it does.
It certainly launched a rant to that effect that has not yet died down.

The behavior of variables
in a closed loop is compeletely different than the behavior of the same
variables when the loop is open. This is why ANY open loop - based model
is irrelevant to understanding purposeful behavior.

Yes, we've all known that for long ages. The whole notion of CSG-L is
based on it That you should even MENTION it here is bizarre.

You preconceive what demons other people may be introducing into this nice
private chapel of PCT, whether the demons be real or no. And you refuse
to take notice of any evidence that the demons might not be real, or might
be mundane normal people--or even angels.

Oh yes, there were lots of witches in Salem. Still are, if you could only
regain the 17th century(?) skills at finding them.

I am not a witch, and I don't think I am possessed by a demon.

Martin

3

<Bill Leach 07 Feb 1994 22:42:36

[Rick Marken (940207.0900)]

Of course I was neither trying to be disrespectful nor trying to ignore
the work that IS being done on these matters (and I am not taking your
response as an indication that you thought that I was).

I presume that the whole point in at least part of the research effort is
to develop models and from the models gain a greater understanding of
just what is going on "inside" the typical subject.

I believe that PCT could be proven to be completely wrong though I
suspect that the real situation will more likely be that PCT will at some
point be recognized as correct but not the "whole story."

I sense that there is some of that already existing within the minds of
PCTer's now. That is, while PCT seems to do a good job of explaining
that which is testable and allows for reasonbly rational explainations
for much behaviour that is not satisfactorily explained by any other
theory, there MAY be "very high levels" where the theory itself does not
explain cognative processes.

Yes. We have to guess at the system parameter(s) and there are
uncontrollable aspects of the environment (little changes in g(o)
becuase of changes in mouse friction, etc). But these turn out to
be very inconsequential details -- as proved by the success of the
basic model in mimicing human behavior.

Again, don't take me wrong int this, but it is the "compensation" for
just such "other" factors that can make the model "close but no cigar."
Naturally, I also believe that such "errors" are introduce due to
assumptions inherent to a particular method of testing will be detected
and corrected as a matter of course in the develpment of additional
testing techniques.

As I see it, you are doing what needs to be done and that is develop the
model as best as you can and then begin trying to stress its ability to
predict behaviour. Where deviations are found, determine their cause(s)
and rework the model if necessary.

IT

I suspect that I am still way too far out on my understanding of the
"debate". I don't for a moment believe that anyone applies IT to the
analysis of information (unless of course they are specifically studying
some souce of information from an IT standpoint) received in any sense as
a part of a persons' normal interaction with their environment.

I do believe that characteristics identified and quantifiable in a known
information stream by IT can have somewhat predictable effects on
perception by the "normal" person.

I don't think that IT itself can predict these pertubations in perception
but rather that experience with human behaviour can be correlated with
known IT produced facts about such information streams.

You might comment on the preceeding three paragraphs as I would like to
know how far out of alignment my thinking might be from the positions of
the "debate".

The bottom line here is this: PCT is about the behavior of variables
in a CLOSED LOOP; information theory is about the behavior of signals
in a commincation channel -- an OPEN LOOP. The behavior of variables
in a closed loop is compeletely different than the behavior of the same
variables when the loop is open. This is why ANY open loop - based model
is irrelevant to understanding purposeful behavior.

Again, this may be viewing things in an improper fashion for PCT
discussions...

We talk about simple or single tasks and we refer to a very simple
control loop consisting of a single perceptual signal, a single reference
signal, a single trasfer function and a single output signal.

Now I know that it is freely admitted that the what we call the
perceptual signal to a control system may well be developed by a large
number of other control loops (and if I understand anything at all about
neurons, an individual neuron may have dozens of input signals).

Unlike control systems that man creates out of (initailly) inanimate
objects, human control systems can choose NOT to control. Now I don't
mean that you can choose not to operate your body but you can definately
decide not only whether you are going to do a particular task but you can
decide how "well" you will do the task (and indeed must make such a
decision).

Thus, while human control systems are CLOSED LOOP, they are anything but
fixed. I don't think that I am saying anything that you have thought
about... and most likely thought a great deal more about than have I.

-bill