I agree there is a big difference between controlling something as a perceptual signal (a neural current) and controlling a “physical quantity”. I could imagine a physical correlate of the perception of speed, but I can’t imagine a physical correlate of honesty or democracy.
I tried to see what Bill meant. (sorry for the lack of source timestamp, a search for phrases should reveal the whole post). Somewhat informative:
BP: It’s been almost 40 years since I started
on this path, but I seem to have a memory of making this very discovery – I can catch an
echo of the big AHA when I realized, thanks to a remark by Kirk Sattley, that a reference
signal could be the output of a higher-level system. This led immediately to seeing that
the perceptual inputs only report the actual state of the external world, not the
reference state as well (in those days, “actual” meant something different to me; I wasn’t
thinking about epistemology). Shivers up the spine! Goals are inside us, not outside us!
It wasn’t long after that that Bob Clark and I led each other to realize that we control
perceptions, not the names of perceptions or the reified correlates of perceptions. That
put the controlled variables inside, too, and we were on the way.
Then later:
The reason for calling this approach perceptual control theory stems from the basis analysis of a living control subsystem. In this closed causal loop, there is only one variable that is resistant to disturbance under changes in the output apparatus, the environment, or the input sensor: the perceptual signal. The control action maintains the perceptual signal near the setting specified by the reference signal. If the sensitivity of the input function, the sensor, were to double, the perceptual signal would remain nearly constant, while the controlled variable outside the system dropped to one half its former value. Changing the link from output to the controlled variable, or changing the sensitivity of the output function to error signals, would also leave the perceptual signal almost undisturbed, while other variables in the loop changed as they must to bring this about. Yet changing the reference signal under any of these conditions will cause the perceptual signal to change in almost exactly the same way.
For this reason, under PCT we characterize behavior as the process of controlling a perceptual signal – or a perception, for short. The term “perception” in PCT does not imply (or deny) conscious awareness of such signals; perception means simply the existence of a signal in a perceptual pathway. Control processes work with or without the presence of consciousness.
If the properties of the perceptual apparatus remain constant, then the observable controlled quantity will correspond reliably to the perceptual signal, and we can speak of controlling the external physical quantity. But under conditions where illusions exist or the properties of perceptual systems are affected by interactions or past history of use, it is the apparent world, not the actual one, that is controlled. So fundamentally, behavior is the control of perception, not of outputs or objective controlled variables. That is the thesis of PCT and has been since the mid-1950s.
AM: There is a bit of a shift in meaning in “controlled variables” to mean “objective” variables in Real Reality, or sometimes to mean “variables perceived by the experimenter”.
[From Bill Powers (961224.1145 MST)]
…
As far as the observer is concerned, what is controlled
is ONLY the CV. The idea that this CV is represented by a perceptual signal
inside the other system is theoretical. We can observe CV, but not p. When
we apply a disturbance, we apply it to CV, not to p. The action that opposes
the effect of the disturbance acts on CV, not p. The Test does not involve p
at all. It involves only observables – i.e., the observer’s perceptions.
The observations have priority; the model comes second, and its only reason
for existence is to explain the observations. When you fool around with
thought-experiments too much, you tend to get the priorities reversed.
And there is also this:
A: You have never observed a CV in your life. At best, you have observed
environmental correlates of them.
BP: It’s the other way around. ALL we can observe of another person’s
controlling is the CV; what we can’t observe is the “CP” – the controlled
perception in the other person.
The CV is defined by the Test, and is basically a perception in the
observer, reified as part of “the environment.” We apply disturbances to
something in the environment, with an expectation of how the disturbance
would change it if there were no control. We strongly suspect the existence
of control if the variable to which the disturbance is applied changes much
less than we expected. The test is completed by showing that preventing the
other system from perceiving the variable destroys control, and that the
reason for the small effect of the disturbance is opposition by an action
of the controlling system. So the CV that we discover exists in “the
environment” and is as objective as any other measure of the environment.
We can be mistaken about the CV, in that the other person might be
controlling a perception derived from the environment in ways different
from our way of perceiving the CV, or might be controlling something
closely related to our concept of the CV but not identical to it, and so
on. We must, of course, be aware of this and not settle for the first
definition that we stumble across.