[Bruce Nevin (2017.07.14.1844 ET)]
So these would be examples of aspects of the (perceived) environment that are stabilized by control but not controlled. It doesn’t resolve the discussion whether environment variables corresponding to the controlled perception are stabilized (Kent’s preference) or controlled (your preference), but it does introduce a different sort of distinction to that discussion.
···
On Fri, Jul 14, 2017 at 3:50 PM, Richard Marken rsmarken@gmail.com wrote:
[From Rick Marken (2017.07.14.1250)]
RM: Most of the debates we’ve been having on CSGNet for the last few years since Bill Powers passed away are repeats of debates that have occurred since the beginning of CSGNet. One debate that that did seen completely new was the one over the power law of movement. But by chance I found a 1995 CSGNet post from Bill that, though not specifically about the power law, is about a phenomenon  that is very much like the power law –  tangential velocity profiles.Â
RM: Like the power law of movement, which has a nearly invariant power coefficient of 1/3 or 2/3 (depending on how the variables are measred), the shape of tangential velocity profiles is found to be nearly invariant across different movement trajectories. And also like the power law, the invariance of these profiles is thought to reveal something important about the fundamental biological and/or kinematic constraints on how organisms produce these different movement trajectories. As Bill put it in the beginning of his post about these tangential velocity profiles:
BP: In a great
deal of modern behavioral research, trajectories of movement
are
examined in the hope of finding invariants that will reveal secrets
of
behavior. This approach ties in with system models that compute
inverse
kinematics and dynamics and use motor programs to produce
actions
open-loop…
RM: So both the power law and tangential velocity profiles are measures of invariant characteristics of movement trajectories that are thought to “reveal secrets” of how movement trajectories are produced. Therefore, it’s not surprising that what Bill says about tangential velocity profiles in his 1995 post, is the largely same as what I (and my co-author) say about the power law in  Marken, R. and Shaffer, D. (2017)
The Power Law of Movement: An Example of a Behavioral Illusion, Experimental Brain Research, 235,
1835–1842).Â
RM: I’ve attached Bill’s post on tangential velocity profiles to this post as a  WORD document and highlighted in italics the parts of his discussion of these profiles that are most relevant to our discussion of the power law. I’ve also added footnotes to these italicized sections that contain quotes or refer to topics in our power law paper that mirror Bill’s discussion of the tangential velocity profiles.
RM: Some things to note if you read the attached post: Bill sees the invariance of tangential velocity profiles in the same way we see the invariance of the power law of movement; as an irrelevant side-effect of controlling. In both cases, evidence that these invariances are side-effects come from the fact that a control model produces movement trajectories with invariant tangential velocity profiles and power law coefficients without considering tangential velocity profiles or power law coefficients. Also, Bill says that research aimed at finding these invariants is going down a “blind alley”. We  implied the same thing by saying that power law researchers were succumbing to a behavioral illusion.Â
RM: The only difference between Bill’s analysis of the invariance of tangential velocity profiles and our analysis of the invariance of the power law coefficients is that we were lucky enough to find a simple explanation for the observed invariance of the power law coefficient.Â
RM: Anyway, I just thought it would be interesting to note that we had discussed an invariance of movement trajectories (in the form of tangential velocity profiles) and the PCT explanation of them was the same as my PCT explanation of the them (in the form of the power law): side effects of control.
BestÂ
Rick
Richard S. MarkenÂ
"Perfection is achieved not when you have nothing more to add, but when you
have nothing left to take away.�
                --Antoine de Saint-Exupery
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