[From Rick Marken (2006.12.14.0910)]
David M. Goldstein, Ph.D. writes:
If we take well thought out, common sitatuions, such as a person driving a car, would there be as much confusion?
I believe the confusion is about a concept, not an experience. The confusion is about the meaning of the term "disturbance". In PCT (and physics, according to Bill) a "disturbance" is a _cause_ of variation in another variable. So when driving a car, variations in cross winds, road wetness and slope, steering wheel position and many other variables are disturbances that simultaneously _cause_ variations in the position of the car relative to the road. But in colloquial use the term "disturbance" is also used to refer to the net _effect_ of disturbances on a variable. So, when driving a car, a sudden change in the position of the car on the road (caused by, say, a sudden gust of wind) will be called a "disturbance" to the car's position. But in PCT, this kind of "disturbance" -- a disturbance that is an effect of causal disturbances -- is just a change in the state of a variable, which may be a controlled variable (like the position of the car relative to the road) or not.
�From the point of view of a person driving a car, a person starts to think that a disturbance is acting when the person's perceptions are changing in ways that are not the result of the person's own actions. A person is pretty good at knowing this.�
Yes. People infer causal disturbances when they perceive a variable being disturbed. But I don't believe people are as good at knowing which disturbance variations are the cause of abrupt changes in a controlled variable as you might think. And they don't need to be. When controlling, people are generally not even aware of the fact that they are continuously compensating for the effects of disturbances on controlled variables. For example, we are not aware of the fact that we are continuously compensating for the effects of gravity as we walk. We just walk where we want.
If we stick to the inside point of view, there doesn't seem to be much confusion, does there? It is only when we take the outside point of view, the researcher studying the situation, that the confusion starts to happen.
I think it's just the opposite, at least when we are talking about the confusion about disturbance as cause versus effect. From the inside point of view I believe we are likely to think of the experienced change in a controlled perception as a "disturbance". On occasion we might try to guess (infer) the cause of a sudden change in a controlled perception, like guessing that it was a gust of wind that resulted in my car moving sharply to the side. But often we are wrong in such inferences (it has often happened that it was me accidentally bumping the steering wheel with my knee that made the car jog to the side; I hope this will keep people from asking me for rides;-) And in most "real life" situations we can even detect the effects of disturbance variables because we are controlling so well.
From the outside point of view -- the point of view of the PCT diagram, basically -- the distinction between disturbance as cause and disturbance as effect is clear. In the diagram, the causal disturbance is the variable d and the result of this (and output) disturbance is the variable qi.
But I think you make a good point by noting the difference between the inside and outside point of view. The inside point of view is the point of view of the controller. The outside point of view is that of the modeler or theorist. I think the confusion about disturbance as cause versus effect comes from problems figuring out how to map one's own experience as a controller onto one's experience as a modeler of control: a control theorist.
�Switching to the researcher viewpoint, let us consider the case of a person 'catching a fly ball', as in baseball. Rick Marken has studied and published about this. Rick, can you review the PCT-specific methodolgy that you used in this research situation. How is it different from a traditional methodolgy approach in this situation?
The best answer I can give to these excellent questions is in my "Optical trajectories..." paper which is available in pdf format at Baseball Catching Research. I also wrote another recent paper on this topic, which has been submitted for publication.
But here is a quick answer: PCT methodology is aimed at determining what perceptual variables people control and how they control them. The basic method involves 1) formulating a hypothesis about a variable a person might be controlling when carrying out a particular task 2) applying disturbances that should cause variations in that variable if it is _not_ under control 3) measure the hypothetical controlled variable to see if it varies as expected as a result of variations in the disturbance 4) if the hypothetical controlled variable varies as expected then it is not controlled, go back to step 1 5) if the hypothetical controlled variable does not vary as expected then it may be under control; return to step 2 using a new disturbance 6) if all disturbances fail to have the expected effect on the hypothetical controlled variable, then tentatively conclude that the variable is under control.
In baseball catching, hypothetical controlled variables that have been suggested are optical acceleration, optical velocity and linear optical path. Disturbances to these variables could be applied by producing known variations in the actual trajectory of the ball to be caught. That is obviously impossible to do in real life so these tests will have to be done using computer simulated trajectories in a virtual reality type environment. Such experiments have not been done yet; if I can get a couple $100,000 (or a very bright student who will work for nothing) these are the experiments I would like to do next, of only to further demonstrate PCT methodology.
Obviously, all this is quite different from traditional methodology, which has the aim of determining what variables (IVs or disturbance variables) cause variations in behavior (output). What is missing from conventional methodology is the concept of a _controlled variable_.
Best regards
Rick
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