Another Allegory

[Bruce_Abbott]

[From Bruce Abbott (970103.1115 EST)]

Bill Powers (970102.1700 MST) --

For "stabilization" substitute "transmutation." We can agree that sometimes
we observe one element being transmuted into another (that's like agreeing
that we can sometimes observe variables being stabilized by actions against
disturbances). A physicist offers one model for how this is accomplished; an
alchemist a different one. The alchemist wants to talk about the
philosophical implications of changing lead to gold; he wants to get on with
that discussion, so he says, "Let's just assume we've found the right
Principles and mental attitudes that will accomplish transmutation. So now
we have lead changing into gold, a base metal changing into a noble one,
which symbolizes the perfection of base human nature through the Grace of
God ... ".

By this time the physicist is jumping up and down in frustration. He butts
in and says "Wait a minute. You haven't shown that transmutation can be
accomplished by any means but the model I've proposed. I don't want to talk
about the perfection of human nature; I want to find out how you think you
can change lead to gold." The alchemist, wounded, says "But just suppose we
have a way to create the right conditions -- is it too much to ask to grant
that for the sake of looking into the implications of having such a means
within our grasp? Aren't you interested in what would happen to the concept
of wealth? Of responsibility? Of ...". To this the physicist simply replies,
"No. I want to know how you accomplish this transmutation. Tell me that and
THEN I'll listen to the rest."

This is not a proper analogy and thus fails as an argument. You can't _do_
anything with your straw-man alchemist's model, but you can learn all sorts
of interesting things about simulation-based stabilization (as compared to
control) from the model I presented, as I noted earlier. And I have already
agreed that coming up with a mechanism to do the modeling is a necessary
next step; in your story your hypothetical alchemist apparently fails to see
the need, other wise I have no idea why the physicist is getting so upset.

I have a similar allegory. In the typical tracking experiment the
participant attempts to keep a cursor located at a specified target
position. The simple PCT model which is offered to account for the data
from such experiments, it is assumed that _somehow_ the participant is able
to perceive the visual input in terms of well-defined objects (e.g., monitor
screen, cursor, target) and _somehow is able to compute the positions of the
cursor and target _relative_ to the screen and _relative_ to each other.
Furthermore, through mere "instructions," the participant "knows" what he or
she is required to do and _somehow_ assembles the necessary control system.

Our physicist friend, who is just as hard on control theorists as he is on
alchemists, demands to know how all this magic is accomplished before he
will even consider taking a look at the control-system model. "Wait a
minute," he says, "you haven't shown how this perceptual system gives rise
to the necessary perceptual input function. And you fail to specify how the
mere giving of instructions leads to the construction of the relevant
control system. The control theorist, wounded, says "But just suppose we
have a way to create the right conditions, such that the pattern of retinal
stimulation gives rise to the requried transformations; just suppose that
such a control system somehow came into being -- is it too much to grant
that for the sake of looking into the implications of having functioning
control systems at work in biological organisms? To this the physicist
simply replies, "No. I want to know how you accomplish this transmutation.
Tell me that and THEN I'll listen to the rest."

Your reasoning cuts both ways. Are you sure you want to maintain this argument?

Regards,

Bruce

[Bill_Powers1]

[From Bill Powers (970103.0950 MST)]

Bruce Abbott (970103.1115 EST)]

I have a similar allegory. In the typical tracking experiment the
participant attempts to keep a cursor located at a specified target
position. The simple PCT model which is offered to account for the data
from such experiments, it is assumed that _somehow_ the participant is
able to perceive the visual input in terms of well-defined objects (e.g.,
monitor screen, cursor, target) and _somehow is able to compute the
positions of the cursor and target _relative_ to the screen and _relative_
to each other. Furthermore, through mere "instructions," the participant
"knows" what he or she is required to do and _somehow_ assembles the
necessary control system.

Our physicist friend, who is just as hard on control theorists as he is on
alchemists, demands to know how all this magic is accomplished before he
will even consider taking a look at the control-system model. "Wait a
minute," he says, "you haven't shown how this perceptual system gives rise
to the necessary perceptual input function. And you fail to specify how
the mere giving of instructions leads to the construction of the relevant
control system. The control theorist, wounded, says ...

You haven't been reading my posts closely enough. All I ask is that the
nature of the problem be identified to the point where the missing machinery
is specified in a plausible way. I believe I said something about at least
providing a box where the missing properties or functions are to go, with
some indication of the inputs and outputs of the box.

When you propose a model in which disturbances are simulated, you're
introducing functions that the basic PCT model doesn't have. You're adding
properties to the model without providing any machinery that would create
those properties. That's what I object to. If you were seriously proposing a
model, you would have to indicate how the effects you postulate come into
being, at least indicating that you're aware of the nature of the problems
that are raised by your proposal. Are you going to equip every elementary
control system with a little pattern generator that will produce the signal
simulating the external disturbance? Are you going to add a computer that
uses available information to determine how to adjust that pattern
generator? Just what information would that be, and how would the system
obtain and use it?

If you were to try to draw a _complete_ block diagram of the arrangement you
propose, even if you had to leave some boxes blank, I think you'd see what
I'm driving at. Every signal you propose has to come from somewhere, as a
function of other system variables or of independent variables affected by
something outside the system. If you look at any PCT or HPCT diagram, you
will find that this is always true: every signal is accounted for in one way
or another. No signal just appears by magic where it's needed in the system.

I think I'm feeling resentful about the way you're playing this modeling
game. When I propose a model, really propose one instead of just
conjecturing to myself about various possibilities, I don't leave any loose
ends dangling. That's why I have to say, so often, "I don't know how to
model that." You're allowing yourself liberties that I don't allow myself.

I still like you, though.

Best,

Bill P.