[Martin Taylor 2018.05.18.12.46]
Much, but not all, of the problem of long unresolved threads on
CSGnet comes from misunderstandings about the intentions of the
writers when using certain words and phrases. Other problems arise
because each of us, novice or self-appointed expert, has a personal
perception of what is and what is not “PCT”, and of what
consequences arise from that personal perception when it is applied
to the real world. I doubt that any taxonomy could incorporate all
the varieties that different CSGnet readers think of when they think
“PCT”, but it is possible to describe some variations that deserve
the name.
A long time ago, in a mailing list far away, we had three
classifications for variants of PCT. I forget the names we used, but
in principle they were: Generic PCT, Generic Hierarchic PCT, and
Bill Powers’s specific version of Hierarchic PCT (HPCT). Some
contributors to CSGnet now write assuming that Bill’s HPCT was
“PCT”, as though the road to enlightenment was only through studying
Bill’s writings, despite the unavoidable self-contradictions that
occur between his early and late writings. As should be the case for
any good scientist, Bill’s understanding of PCT developed, over the
half-century and more that he studied the control of perception. To
base discussions of PCT only on fine interpretations of Bill’s
writings, especially the earlier ones, is a sure way to create
disputes. Just as an exhaustive study of any ancient writings by
several people will do, the various Koranic, Biblical, or Talmudic
scholars come to different conclusions about the truth that is
hiding behind the Holy Writ of PCT.
My own preference is to work from the other end, to consider Nature,
using my own interpretation of Bill’s powerful insights as a
valuable but not infallible guide. I ask questions such as:
Supposing this or that variant form of PCT happened to be correct,
what would we observe? What limitations does Nature impose on
control, and is this or that version of PCT consistent with those
limits? How could we know whether what we perceive has a counterpart
in properties of the environment in which we live? Etc., etc… One
class of questions concerns whether observed effects depend on
Generic PCT, Generic hierarchic PCT, HPCT, or some other variant, of
which there may be many.
What did we mean by these three levels so long ago? Generic PCT
simply means a theory that organisms create internal variables that
correspond to some patterns of sensory data based on things and
events in the real environment, and act to influence those patterns
to conform to internal “reference variables”. Generic PCT specifies
nothing about the form of these control loops or how one relates to
another. They might all work independently, they might have all
sorts of cross influences or network structures of interaction.
Generic PCT allows almost anything that involves control of internal
variables by action on the environment outside the organism.
Generic Hierarchic PCT (GHPCT) is a specific refinement of Generic
PCT, one of many possible structures of interaction among control
loops. The specific refinement is that the internal (perceptual)
variables individually represent identifiable entities or structures
in the environment. Those that are controlled come in simple and
more complex forms, the more complex being built on the simpler to
form a kind of “tower of complexity” with very complex perceptual
forms at the top and raw sensory data at the base. GHPCT allows any
kind of relationship among the functional processes that lead to
control of these perceptions.
Powers's Hierarchic PCT (HPCT) is a specific refinement of GHPCT, in
which different levels of complexity and a specific form of
interconnections among the functional processes is defined. Although
Powers did not insist on it (at least at the lowest levels), one
might include as a necessary component of HPCT the eleven types of
increasingly complex perception Powers proposed. Of course, I am not
saying that Powers developed his version of PCT by refining GHPCT.
Far from it. The reverse, a generalization from Powers’s HPCT to
GHPCT, would be nearer the truth.
Another way one might categorize varieties of PCT is according to
how the PCT structures evolve over generations and within
individuals. Among other possibilities, we might include e-coli
reorganization, reinforcement learning, Hebbian cell-assembly and
random connection making and breaking, all globally, in modules, or
in hybrid form. Powers’s HPCT incorporates e-coli reorganization
generically, but not in any formal and specific way. Different
variants of Powers’s HPCT would depend on different understandings
of how reorganization functions to change the control hierarchy.
Already we have listed over a dozen possible varieties of PCT, and
these are far from exhaustive. For example, there are other species
of GHPCT, and forms of Generic PCT that are highly structured but
not hierarchic. I don’t know whether anyone has seriously proposed
the following as a PCT variety, but in the silico-acoustic world the
inverse Fourier transform of the log Fourier transform is a useful
tool. Imagine a model in which the controlled perceptions were
quasi-spectral relationships among vectors of logarithmic values.
Structurally, this kind of thing was proposed (a long time ago) for
the distributed character of perceptions to protect them against
focal brain damage, and maybe control of spectral representations
might be functional. Many years ago, when I visited the Swedish
Defence Research Institute I was shown how re-inverting the phase
spectrum of a spatial Fourier transform after losing the amplitude
information produced a good outline drawing of the original
picture. Neural systems seem well suited to doing this kind of
thing, but is it well suited to control in a dynamic environment?
One could actually consider the plethora of specific perceptual
functions of Powers’s HPCT at a given level of the hierarchy as a
kind of quasi-spectral transform, mathematically.
One specific variant of GHPCT that I do like is based on the
apparently different functional tendencies of the brain hemispheres.
This variant is like Powers’s HPCT except that there is no category
level as such. Instead, each of the other perceptual types may
interface with a category process that produces category values and
performs logical operations on them ( (left-brain function))
interacting with analogue values (right-brain function) at each
level. Again, there are probably many variations on this theme, all
producing different variant forms of PCT.
My main point is not to advocate for any changes to Powers's version
of HPCT, but to show how easily variant forms can be imagined. This
being the case, how many more subtly different varieties of PCT may
exist in the hidden assumptions each of us has when we discuss “PCT”
on CSGnet and get into unnecessary arguments. In most cases, so long
as the assumptions remain hidden, arguments are unresolvable about
what is or is not PCT and about what is or is not true of Nature
viewed through a PCT lens. Even if by some lucky chance the
conflicting assumptions are revealed, it is as like as not that no
experiment has been done that could distinguish between them, and
the only rationale for choosing one over the other would be Ockham’s
Razor – and that particular razor shaves differently for different
people (see for
the explanation).
My second point is simply to try to shake up a bit the idea that
some people seem to hold, that “PCT” means exclusively the
constellation of concepts about which Powers wrote. That happens to
be the version of PCT that is by far the most studied and tested,
but it is far from the only one that is possible, and many of the
others would automatically have provided identical results to any
tests that have as yet been applied to the Powers version, including
all studies such as the Test for the Controlled Variable, which
examine only a single isolated control loop.
Martin
“”
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http://www.mmtaylor.net/Academic/ockham.html
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A good scientist always tries to find what might be wrong about
what s/he firmly believes*