AM: I don’t see it. More examples of your definition of side effects, please.
RM: In the rubber band demo if you, as E, apply disturbances to the position of the knot so that S has to move her end of the rubber band in a way that traces out a perfect rendering of Botticelli’s Venus on the Half Shell , then that picture is a side effect of S controlling the position of the knot.
AM: Ok, makes sense. Any properties of qo, the final trajectory are a side effect of keeping qi stable.
AM: The problem is that this definition of side effects is in conflict with your definition of a behavioral illusion. If the contour of Venus look exactly like the template you wanted to get, this tells you something very important about the control system that made it. For one, it is a high-gain control system, at the speeds that you gave it. If the contour of Venus looks somewhat distorted, the gain was not so high, the errors were not well compensated.
RM: Yes, but you know all that (or can know it, using modeling) because you know what the controlled variable is: the position of the knot. These are the kinds of things manual control theorists have been able to find out because they study control in situations where they know what the controlled variables are (or should be).
RM: What is unique about PCT Is that it posits that ALL behavior is the control of perceptual variables. This hypothesis is explicit in the hierarchical PCT model of purposive behavior. The hypothesis is that organisms control a hierarchy of different TYPES of perceptual variables. This hypothesis has been subjected to very little testing and yet it is treated as though it is a known fact. I’m trying to move PCT research in the direction of testing Powers’ hypothesis about the control hierarchy, a hypothesis (and a description of some of the evidence supporting it) that takes up at least 60% of B:CP.
AM: But in a way, I do agree with you, the power law does not tell you anything definite about the system until you find the controlled variables. It might be that it is an intended effect, it might be it is not. Proof and demonstration only by models and experiments.
AM: No so fast.
AM: The same thing goes for “a behavioral illusion” in your power law papers. If it turns out that the power law is the main effect, that the trajectory is the controlled variable, or the instantaneous affine velocity is the controlled variable, both of which you suggested might be controlled; then the power law is not a side effect, it is the main effect, intended and achieved.
RM: I agree. But I consider it very unlikely that the power law itself is a controlled variable; a person would have to be continuously perceiving whether the velocity and curvature of their movements had the appropriate power relationship. But if you could figure out a way to test that hypothesis (or the more plausible one about control of affine velicity) that would be great.
AM: On the other hand, if some other variable is controlled, then the power law is a side effect, but it does tell you something about the control system. The exact speeds where the power law appears tell you something about, for example, force production constraints of the organism, or something about the interaction of the body and the environment in the loop, things like friction, inertia. etc.
RM: I don’t think so but if you do figure out a way to test for the variables being controlled when organisms move their limbs then that in itself would be a wonderful discovery, from my perspective anyway.
RM: Perhaps now is the appropriate time for me to confess that I don’t consider myself to be a PCT research maven. I’m pushing research based on testing for controlled variables because I know that’s the right way to study the behavior of living control systems and I know that’s the kind of research Bill Powers was hoping researchers would start doing. I haven’t done a lot of this kind of research myself but I have some some (the best example, I think, is my object interception research where the test for controlled variable was used to choose the best of three different hypotheses about the variable controlled when intercepting moving objects).
RM: I’m mainly pushing testing for controlled variables because I would like some help doing this kind of research from people, like you Adam, are a lot smarter than I am. This is a very new approach to studying the behavior of living systems and it will take some ingenuity to figure out how to do it properly since it has never really been done before.