PCT and Tensegrity

at 13:00 PST 980104 David Wolsk provided a reference:

From Bruce Gregory (980102.1053 EST)]

Martin Taylor 980102 01:02

My experience is that a lot of them say "it can't be that simple. People
are more complicated than that." It's hard to get across the idea that
this complicated world is made up of simple atoms that connect in simple
ways--but there are a lot of them interacting, which is what makes life
interesting. It is even harder to get across the idea that the obvious
complexity and beauty of human experience can come down to the simple
interactions among many simple control systems.

Excellent observation. After all, many chemists were prepared to abandon the
atomic model as late as the middle of the nineteenth century.

I suggest the Ingber article in the Jan 98 issue of Scientific American: THE
ARCHITECTURE OF LIFE ...... tensigrity and self-assembly ..... simple ideas,
magnificent outcomes.

[From Rick Marken (980107.0745)]

David Wolsk (980105) --

I suggest the Ingber article in the Jan 98 issue of Scientific
American: THE ARCHITECTURE OF LIFE ...... tensigrity and
self-assembly ..... simple ideas, magnificent outcomes.

This article is available on the Web at:


I was less impressed by this article than you seem to have been.
But I'm not a cell physiologist so maybe it's just above my head.
But it seemed to me that "tensegrity" is just an ugly new
name for what, in psychology, was called a "coordinative stucture"
(later transforming itself into the trendier "attractor" and
"complex dynamical system").

The author describes "tensegrity" as "structures [where]...tension
is continuously transmitted across all structural members". According
to the author, this property of tensegrity structures explains
how..."the structure stabilizes itself through a mechanism that
[Bucky] Fuller described as continuous tension and local compression".

So tensegrity (mutual interacting forces) _stabilizes_ structures.
The author (Ingber, who has more degrees than I have complaints
about conventional psychology) seems to think of this stabilization
as a control process because he describes how tensegrity works in a
section of the paper called "How Mechanics Controls Biochemistry".
Of course, Ingber might be using the term "control" here to mean
"cause", but then tensegrity theory becomes a whole lot less
interesting as a model of living systems.

It seems to me that Ingber's article (like most scientific articles
on living systems) suffers from a lack of understanding of the
nature of control itself. If, for example, structure is controlled
then it will be _protected_ from disturbance. This doesn't mean that
the structure will be restored to its original state after a transient
disturbance has been removed (which is what happens with structures
"controlled" by transegrity). It means that the stucture _remains_
in its original state _while_ it is being disturbed _and_ after
the disturbance is removed (which is what _does not_ happen with
structures "controlled" by transegrity). Control of structure means
that disturbances to the structure will have virtually no effect on
that structure.

It seems to me that the "coordinative structures" and "dynamical
systems" types, who were trying to explain the stability of certain
"behavioral structures", make exactly the same mistake as Ingber
makes when using transegrity to explain the stability of certain
biological structures; they all mistake "equifinality" -- which is
the return of some variable (such as a variable aspect of strcuture,
such as shape of location) to its the original value after a
disturbance -- for "control" -- which is the _maintainance_ of a
variable at a reference value _while_ it is being disturbed.

Equifinality charaterizes the behavior of a mass on a spring; pull
the mass down and it returns to its original position when it is
released. Control characterizes the behavior of the cursor in a
tracking task; "pushes" and "pulls" on the cursor have little or
no effect on the cursor's position.




Richard S. Marken Phone or Fax: 310 474-0313
Life Learning Associates e-mail: rmarken@earthlink.net