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- Date: Sat, 9 Jan 1993 16:47:00 GMT
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- From: Hortideas Publishing <0004972767@MCIMAIL.COM>
- Subject: S-R "Part" of PCT models; stiffness tensor
- Lines: 65
-
- From Greg Williams (930108)
-
- >Rick Marken (930108.2030)
-
- >So an SR model is PART and PARCEL of the control model.
-
- But I thought that the typical S-R model was construed by PCTers as containing
- reference ONLY to observable variables and as purely descriptive at the level
- of the phenomena being DESCRIBED, and that the typical PCT model was construed
- by PCTers as containing observable variables AND hypothetical underlying (or,
- eventually observable, but at any rate INTERNAL to the organism) variables and
- as a generative model postulating mechanisms at a level below the level of the
- phenomena being EXPLAINED. The feedback part of the PCT model for tracking
- (the second equation, relating C to H and D) contains only observables
- (observable to the experimenter, that is) which are at the level of the
- phenomena to be explained. Where are the underlying variables INTERNAL to the
- organism?
-
- As I've said before, IF PCTers made a generative model of the "noise"
- exhibited by the tracker, using hypothetical internal variables, THEN the "S-R
- PART" of the PCT model WOULD be different than the behaviorist's input-output
- equation, because the behaviorist would add a statistical noise term to
- DESCRIBE the noise, instead of a term to GENERATE the noise.
-
- So I think that, with regard to PCT models of tracking TO DATE, the
- behaviorists would have no difficulty in adopting the same models. They would
- interpret BOTH equations as purely descriptive and as containing only
- observable variables. And they would see nothing revolutionary in PCT. If
- there is feedback from "responses" to "stimuli," they would include that in
- their "descriptive" models without wincing. But if PCTers went on to include
- in new models some underlying hypothesized variables to generate "noise," so
- as to be able to predict cursor position adequately for True Science, then
- there would be two upshots: (1) the behaviorists' models would be genuinely
- different from the new PCT models; (2) if the new PCT models could predict
- cursor position very accurately, and the behaviorists' descriptive models
- could not, then the behaviorists would need to take the PCT models (and,
- indeed, the whole notion of needing EXPLANATORY generative models using
- underlying internal variables) seriously -- PCTers would have solved a problem
- that the behaviorists couldn't solve, and would have beat them at their own
- game. The sort of PCT-boosting result which I was talking about the other day.
- Of course, whether it is POSSIBLE in the near term to develop such Truly
- Scientific generative models for tracker "noisiness" is another question,
- about which I have previously raised concerns. But it would be interesting for
- those who aspire to be True Scientists to try. The potential rewards might
- well repay the efforts.
-
- -----
-
- >Avery Andrews 930110.1700
-
- >Can anyone tell me a quick story about what a stiffness tensor is (or at
- >least the kind of book title to find it described in).
-
- Look in a text on mechanical behavior of materials (solid mechanics). A
- dimensional spring can be modeled as having a (generally different for each
- point on its extension curve, unless it is linear) scalar stiffness, k, such
- that the force to stretch or compress the spring, F, depends on the current
- amount of stretch (from rest), x, via the function F = k x. In a three-
- dimensional solid, there are SEVERAL stiffnesses (which, together, make up the
- stiffness tensor) because there are SEVERAL ways to stretch and compress the
- solid.
-
- As ever,
-
- Greg
-