[from Gary Cziko 950102.1450 GMT}
Rick Marken (950102.2100) said:
The general linear model explicitly
views the organism as a "transfer function" that transforms input
variables (the IVs) into output variables (DVs). The assumption is that
the coefficients of the terms in the model tell you something about
how the organism responds to input variables. It is this assumption --
which is the basis of the application of what I call IV-DV methodology
in conventional psychology -- that I say is false when you are dealing
with a negative feedback system (ie. a living organism). This is why I
say that conventional IV-DV methodology is useless in the study of
living control systems.
I wish there were some way I could do my version of the rubber-band demo to
illustrate these points on the net. I think I've described it before on
the net and I promise to perform it in July in Durango, but this discussion
is calling for it again.
We all should know how to tie two similar rubber bands together. Now to
the end of one of the rubber bands tie a length of string of about 10
inches or so. This, plus a target spot (e.g., a penny on a table, a mark
on a blackboard) is all the equipment needed. Now you need a subject (she)
and a traditional lineal cause-effect IV-DV psychologist (he) who tries the
explain the subjects behavior (you are the experimenter).
First ask the subject to keep the knot over the target as she holds one end
of one rubber band and you hold the end of the other and provide
disturbances. Ask the psychologist to explain the subject's behvior in the
traditional way. He will explain that the subject is moving her hand in
response to your (the experimenter's) hand movements. While PCTers like
Marken would say that this is an incorrect and useless explanation, it does
allow very good predictions of what the subject will do in response to the
experimenter's actions BUT ONLY AS LONG AS CONDITIONS DO NOT CHANGE
CONCERNING THE RELATIONSHIP BETWEEN THE EXPERIMENTER'S HAND MOVEMENTS AND
ITS EFFECTS ON THE KNOT JOINING THE TWO RUBBER BANDS.
So now we change this relationship. You (the experimenter) now pull on the
STRING with your other hand, letting the rubber band slip through the
originally disturbing hand which now remains immobile. The psychologist
would have to predict now that the the subject will not move her hand. But
he is wrong as the subject behaves to resist the disturbances coming from a
new source. Then hold the string steady while the originally disturbing
hand moves up and down the rubber band without pulling on it. The IV-DV
psychologist would have to predict from his original explanation that the
subject will move her hand in response to the experimenter's
movement--wrong again.
So while the IV-DV explanation of behavior is not totally useless and can
make useful predictions if disturbing conditions do not change, it is
demonstrably inferior to the explanation provided by finding the controlled
perceptual variable. Knowing that a driver will turn the steering wheel to
the right while travelling straight west in response a gust of wind form
the north does not allow one to predict what will happen if the roadway
begins to slant to the left. Knowing what the driver is controlling
(keeping his car on the road) allows us to make such predictions. I also
seems to me that such purposeful explanations of behavior are commonly used
by people who have not been tainted by formal study of psychology.
--Gary