IT and PCT (history)

<Martin Taylor 940205 16:15>

Rick Marken (940204.1900)

Rick complains that my repeated mentions of a bit of net history are
getting tiresome. I agree that the topic is getting tiresome, and that
Rick has a valid point in his complaint.

The test conditions were prespecified by Rick to be acceptable. When we
did that demonstration, the grounds shifted very rapidly under our feet,

This is getting tiresome. You are trying to make it sound like I
am the lone, unreasonable PCTer who just won't accept the contributions
of IT. The fact of the matter is that at least two PCTers besides myself
(Tom and Bill) have been as actively unconvinced by your test results as
I have. All you were able to do in the great "test" that you think
should have shut me up is solve for o given p, r, k and the fact that
p = o + d and o := o + k(r-p). You did this while I was busy stringing
you along, giving you more and more information (which the control
system couldn't possibly have, a fact that you blithely ignored)
to let you think that the input-output calculations would work.

Sorry, Rick. You are at least partly right. Bill Powers did join you in
saying that the original demonstration would not come out the way we said
it would (and did). I've been back to the original postings (and boy,
were there ever a lot of them). Here are some key ones. You will note
that I pointed out, and you rejected, the problem that the output does not
actually mirror the disturbance, a point that you then turned around and
made the core of your "stringing along". However, I don't think that your
postings quoted below quite support your claim that you were "busy
stinging me along." You were quite happy to know that my demonstration
(now called trivial) would not work when put to the test. All that
so-called "stringing along" happened after you were shown to be wrong.

Here are two key quotes from Rick Marken (930331.0800)

If I understand the
claim, oft repeated, Rick means that no function that takes as input
(a) the perceptual signal and (b) any other signal that is agreed to have no
information about the disturbance can reconstruct the disturbance, but
that nevertheless the disturbance is mirrored in the output.

I'll buy it.

and

Let us see whether a function can be constructed that takes these two
inputs [The reference signal and the perceptual signal; MMT now]
and produces a signal that matches the disturbance. If so, I
would consider it conclusive evidence that information about the disturbance
is to be found in the perceptual signal.

OK!

I'll stop mentioning this, as I find it equally tiresome, when you stop
proclaiming that there is no information about the disturbance in the
perceptual signal. And if you want, I'll repost all the places where
Allan and I made explicit what we meant by "disturbance," which is
exactly what we all seem to agree now is meant by the term. And even
the so-called "stringing along" postings, if you insist.

History is better with reference to the original sources than when
based on fallible memory.

ยทยทยท

==================================================================
Now the history, and at the end a couple of comments.

[Martin Taylor 930330 11:20]
(Rick Marken various)

(930315.1500 as an example)

"... THERE IS NO INFORMATION ABOUT DISTURBANCE IN THE PERCEPTUAL SIGNAL
CONTROL SYSTEM. This means that THE PERCEPTUAL INPUT TO A CONTROL SYSTEM
CANNOT BE WHAT CAUSES THE OUTPUR OF THE SYSTEMN (sic) TO MIRROR THE
DISTURBANCE."

Let's consider a thought experiment to test this. If I understand the
claim, oft repeated, Rick means that no function that takes as input
(a) the perceptual signal and (b) any other signal that is agreed to have no
information about the disturbance can reconstruct the disturbance, but
that nevertheless the disturbance is mirrored in the output.

I'll leave the logical problem with the "mirroring" unaddressed, and
assume that Rick accepts as correct what he says, that the output
mirrors the disturbance.

In my thought experiment, I will take the ECS, and add a simple function
that takes as its input the reference signal to the ECS (which I think we
can agree has no information about the disturbance) and the perceptual
signal, which Rick CAPITALIZES as having no information abou the disturbance.
Let us see whether a function can be constructed that takes these two
inputs and produces a signal that matches the disturbance. If so, I
would consider it conclusive evidence that information about the disturbance
is to be found in the perceptual signal.

             ------------> Signal X (which should match the disturbance)
            >
       mystery function M(r, p)
        ^ ^
        > >
        > > V (reference signal R(t) into ECS)
        > > >
        > <-------|
        > V
        >---------->comparator------- error = P-R
        > >
    perceptual output
     signal P(t) function O(error)
        ^ |
        > V
        > output signal
        > (accepted as mirroring the disturbance)

-------------------------------------------------------------------

If Signal X matches the disturbance, the perceptual signal must be the
route from which the mystery function M(r, p) gets the information about
the disturbance. Right?

Now let the function M be indentical to O(R-P). Signal X will then be the
negative of the output signal, which is the disturbance. The only question
here is whether O(error) is a function or a magical mystery tourgoodie. I
prefer to think we are dealing with physical systems, and that O is a function.
Therefore, information about the disturbance is in the perceptual signal,
and moreover, it is there in extractable form.

QED.

(Actually, QED is too strong, since I imagine most of us will want to
challenge Rick's claim that the output mirrors the disturbance. But that
way lies the argument to information rate, which I will pursue whether or
not Rick accepts that way out of the Q that ED.)

Martin

======================================================
[From Rick Marken (930331.0800)]

Martin Taylor (930330 11:20) --

Let's consider a thought experiment to test this.

EXCELLENT THOUGHT EXPERIMENT! Now let's do it as a simulation,
shall we?

If I understand the
claim, oft repeated, Rick means that no function that takes as input
(a) the perceptual signal and (b) any other signal that is agreed to have no
information about the disturbance can reconstruct the disturbance, but
that nevertheless the disturbance is mirrored in the output.

I'll buy it.

I'll leave the logical problem with the "mirroring" unaddressed, and
assume that Rick accepts as correct what he says, that the output
mirrors the disturbance.

What's the "logical" problem with the "mirroring"? You can look at
the data from our tracking experiments and see that o = -d to within
a few pixals throughout an experimental run. When both o and d are
measured in screen units, the time traces of these two variables will
be symmetrical about a line corresponding to the fixed screen position
of the target. I call this characteristic of the graph "mirroring".

In my thought experiment, I will take the ECS, and add a simple function
that takes as its input the reference signal to the ECS (which I think we
can agree has no information about the disturbance) and the perceptual
signal, which Rick CAPITALIZES as having no information abou the disturbance.

Excellent! For simplicity, let's make the reference signal a constant
when we simulate your model. But a variable r will work too -- just
trying to keep it simple.

Let us see whether a function can be constructed that takes these two
inputs and produces a signal that matches the disturbance. If so, I
would consider it conclusive evidence that information about the disturbance>is

to be found in the perceptual signal.

OK!

            ------------> Signal X (which should match the disturbance)
           >
      mystery function M(r, p)
       ^ ^
       > >
       > > V (reference signal R(t) into ECS)
       > > >
       > <-------|
       > V
       >---------->comparator------- error = P-R
       > >
   perceptual output
    signal P(t) function O(error)
       ^ |
       > V
       > output signal
       > (accepted as mirroring the disturbance)

-------------------------------------------------------------------

If Signal X matches the disturbance, the perceptual signal must be the
route from which the mystery function M(r, p) gets the information about
the disturbance. Right?

Right!! I completely agree with your proposal as diagrammed above.
I think a good first candidate for M(r,p) would be the function
O(r,p), right? Ah, I see you think so too:

Now let the function M be indentical to O(R-P). Signal X will then be the
negative of the output signal, which is the disturbance.

It is at this point that experience will triumph over the "obvious"
conclusions of your thought experiment. I think it's time to fire up
the simulator; really!

The only question
here is whether O(error) is a function or a magical mystery tourgoodie.

Your magical mystery tour will really begin when you run the simulation!

I
prefer to think we are dealing with physical systems, and that O is a

function.

Therefore, information about the disturbance is in the perceptual signal,
and moreover, it is there in extractable form.

QED.

And a right excellent proof i'tis. Now try the simulation.

Best

Rick "There is no information about the disturbance in controlled
perception" Marken

===========================================
[From Bill Powers (930331.1030 MST)]

The diagram you gave, below, won't work:

             ----> Signal X (which should match the disturbance)
            >
       mystery function M(r, p)
        ^ ^
        > >
        > > V (reference signal R(t) into ECS)
        > > >
        > <-------|
        > V
        >---------->comparator------- error = P-R
        > >
    perceptual output
     signal P(t) function O(error)
        ^ |
        > V
        > output signal
        > (accepted as mirroring the disturbance)

If the reference signal is zero, the signal X won't mirror the
disturbance.

=======================================

[From RIck Marken (930331.2100)]

But no information about the disturbance
can be recovered from the perceptual signal all by itself (or, as
you will see from the simulation, with the help of the output function).

==========================================
and even now

Rick Marken (940204.1900)

That's the whole point
of the "information in perception" debate; you can't tell anything about
the disturbance(s) given the perceptual signal.
....
But if you want us to think there
anything to IT (in terms of understanding purposeful behavior), you'd
better tell me that it does more than say "you can solve for d in d=p-o
if you are given p and o".

How many months have I been beating my head against the wall telling
you not only just that, but also that such a solution is irrelevant,
uninteresting, and useful only to demonstrate in an extreme way that
there is information about the disturbance in the perceptual signal.

Tiresome, indeed.

Martin