[From Bill Powers (950530.0945 MDT)]
I think I have resolved the problem with the skipped lines in my
posts. Let me know (thanks, Bill Leach).
···
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Luke Aitken --
You have already registered and sent in your deposit. Guess you
forgot. Mary's email address is the same as mine:
powers_w@fortlewis.edu. That's a change from our previous
address.
The meeting dates are July 19 - July 23. The first day is arrival
day with an evening meeting to get organized. The last day is
departure day.
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Bruce Abbott (950529.1955 EST) --
By the way, did you read Bill Powers' nifty little
description of hummingbird behavior? On second thought, you
wouldn't find it of interest--no application of the TEST and
all that, just description from the point of view of the
external observer, with a little speculation about possible
controlled variables thrown in.
I think that my informal presentation may have disguised the Test
too well. The controlled variables I had in mind were the
distance of the bird's head from the feeder and the orientation
of the head relative to a feeding port. The disturbances were the
swinging of the feeder, the twisting oscillations of the feeder,
and the wind velocity. I observed that the controlled variables
(during feeding) remained essentially constant, while the
expected effects would be a variation in both the distance and
the orientation (expected, that is, under the hypothesis of no
control, so that the effects of the disturbances would not be
opposed by the bird's actions).
A similar description of the fly's landing would have to include
descriptions of disturbances which, unopposed, would have
predictable effects on the observed landing pattern. To
demonstrate control of any particular variable in that pattern,
we would have to show that for each disturbance, the fly altered
its behavior in such a way that the controlled variable was
immediately restored to its former state, or prevented from
changing away from that state.
This is what was missing from the Nachitgall description of the
fly's landing pattern. The mere repetition of the pattern is not
sufficient to demonstrate control. We must show that disturbances
tending to change the pattern are resisted.
Suppose we set up a flow of air parallel to the surface on which
the fly is landing. We might find (I'm guessing) that now the fly
does not orient its body at a steep angle to the surface, but
approaches at a shallower angle when flying upwind. This would
tell us that the angle of the body relative to the surface is not
a controlled variable, but is part of the variable actions used
to control some other variable. Perhaps what we would find is
that the direction of approach to the surface rather than the
angle of the body is under control. The body angle is simply
varied to keep the direction of approach the same. Of course if
you always observe without any disturbances present, you can't
tell that the body angle is not under control.
A parallel case would be observing how a boater rows across a
body of water, a lake. If we observe that the rower points the
boat toward the distant dock, we might conclude that the
direction of the bow of the boat relative to the dock is a
controlled variable. If, however, we do the same test on a river,
which disturbs the path of the boat relative to the distant dock,
we will find that the bow of the boat is aimed upstream, while
the direction of progress of the boat continues to be a straight
line toward the dock. So the direction of the bow is ruled out as
a controlled variable, and the direction of progress (or some
perception related to it) is likely to be under control.
In the Srinivasan article described by Avery Andrews, the Test
was actually applied. Various aspects of the environment were
deliberately altered, to test the idea that visual outflow was
the controlled variable and to rule out other aspects of the
perceptual situation as being stabilized against disturbances.
That is why this work was considered to be a "good PCT
experiment" even if Srinivasan didn't formalize what he was doing
in PCT terms. The lack of such disturbances was the reason that
the Nachtigall description was not considered a "good PCT
description." Nachtigall didn't describe any disturbances.
Without disturbances we can't identify controlled variables
experimentally.
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Bill Leach (950529.21:34 U.S. Eastern Time Zone) --
I don't believe that Rick, and I certainly know that I, did
not assume that what was quoted was ALL that exists in the
book but _please_ both of you guys (Bill and Bruce) how
about honoring the quite obvious intent (at least to me) of
Rick's orginal request...
Why run this like a mid-term exam? I've been waiting for someone
to explain to Bruce why the Nachtigall description was not a good
PCT description, but as you can see, I have finally provided the
explanation myself. That would have been an easy way to avoid the
squabbles. I can only conclude that there is some other goal
involved, like showing who knows most about PCT. What a bore.
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Your comments re Hans' model are appreciated. Also your efforts
in looking up definitions of control. I'd like to see some more
-- and by the way, why not cite some of those horrible examples?
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Hans Blom (950530) --
I'll try out your new demo today and comment later. If you think
that "frequency makes no difference" you must have forgot a great
deal of the basic control theory you once knew, or else you're
not saying what you mean.
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Joel Judd (950530.0830 CST) --
Rick M. and Bill P. (950529):
> read EVERY SINGLE WORD (of the Bible)
I have, too, and actually find it MOST relevant to PCT.
However, since it was never intended to be a treatise on
human psychology, maybe it shouldn't consistently be
criticized for being a poor one. Or perhaps it should be
read with a different purpose in mind...
I think that you and I read the Bible using different premises.
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Best to all,
Bill P.