[From Bill Powers (2009.04.28.0646 MDT)]
David Goldstein (2009.04.27.18:00 EDT) --
Here is something I wrote. It was inpired by observing my one year old granddaughter, Lilah, trying to eat with a spoon.
It was also inspired by my Friday lunch with Dr. David London, a colleague, as I tried to explain the concept of control.
Let's reorganize this thread a little. I think examples like yours are great, but I'm really looking for ways of translating from PCT into ordinary language and vice versa. Your examples and those offered by others are good, but let's try to tie them to teaching PCT.
I gave a list of words to avoid, as a way of forcing attention toward the concepts behind them. But suppose we try setting it up like this: Define each of these terms without using any of the others:
control
disturbance
input quantity
input function
perceptual signal
reference signal
comparator
error signal
output function
output quantity
feedback function
That's the whole loop.
The difficulty with just giving examples is that the listener doesn't know which part of the example is important or what each part is supposed to convey. I think new learners need a little more help than that.
Take the first word, control. How does controlling something differ from reacting to a stimulus or planning an action and then carrying it out? Examples are useful for this -- you can use examples to show the differences. As you develop the explanation you'll have to think of ordinary terms, or use parts of your example, to talk about disturbances and the other terms above without naming them. How would you explain putting food in your mouth as a response to a stimulus? As a planned action? And as a control process?
The list consists of general terms; what you want in your description is an equal level of generality. That is, control isn't just putting food into your mouth, it's any process that .... blah blah blah. You have to try to generalize a little so the particular example doesn't become too central. I guess what I'm saying is that after giving an example, you should pause to generalize it, maybe mentioning a different example and pointing out what is the same in both of them. Putting food in your mouth, threading a needle. Give some guidance about what the important general idea is. You don't want to leave the impression that control works only for eating.
A teacher of expository writing would probably explain what I'm after better than I can. But you're all smart guys out there, you can figure it out.
Best,
Bill P.