Evolution and Control (was(Understandingness ...))

Re: Evolution and Control (was(Understandingness
[Martin Taylor 2004.]

From Dan Mayer

I said in my last
post that I was leaving but I saw this new post and felt it only
gentlemanly to respond.

[From Rick Marken

And why do you suppose we move and navigate in the environment?
Perhaps it’s

to get to places we want to get to? Which involves acting to reduce

discrepancy between where we are (perception) and where we want to

(reference)? That discrepancy being called “error”?
Contrary to your view

of my view of behavior, I know that people (and all living things,

plants) have evolved to move or stand still, as required, to achieve


Yes Rick, you quite
right in all this. The problem, if there is one, is that your view is
a mechanistic view of how we move. Llinas has focused on Why we

I’m afraid I have to acknowledge that I
haven’t read Llinas. But I don’t think that disqualifies me from
refuting Dan’s statement that the PCT view is a mechanistic view of
how. To me it’s an answer to why. Since according to Dan, Llinas’s
book is: “a very well thought out compilation of 25 years of
research in neuronal neuroscience” it has to be irrelevant to the
answer to the “why” question.

Here’s part of what I wrote in my Editorial
for the International Journal of man-Machine Studies Special Issue on
PCT. Consider its repetition as a New year’s Manifesto, if you

Necessity of Perceptual Control Theory

There is
one overwhelming fact about life: to survive, any organism must in
some way stabilize its essential internal chemistry in the face of
disturbances from a turbulent outer world. Every living thing that we
see is a member of a species that behaves so that at least some
members of the species stabilize their internal chemistry long enough
to propagate their genes.

Protection against the buffeting of the outer world can be done in two
ways, and life employs them both. The first way is to develop passive
armour, such as a membrane, skin, or shell. But the armour cannot be
so perfect as to isolate the organism completely from the outer world;
if it did, the organism would die an entropic death. Just to sustain a
minimal internal organization, any living thing must at least take in
high-quality energy from the outer world, and excrete disorganized
waste energy. Most do much more.

The second way an organism can protect itself against the disturbances
of the world is to counter them as they occur, actively and
powerfully. To do this, the organism must be able to sense important
states of the outer world, it must be able to compare the sensed
states with desirable conditions for those states, and must be able to
act so as to bring about and maintain the desirable conditions. “To
sense” means to alter some internal state, such as a chemical
concentration or a neural firing rate, in correspondence with changes
of something in the outer world. In Perceptual Control Theory, such an
internal state is called a “perceptual signal,” and the value of a
perceptual signal is a “perception.”

“Perception,” in PCT, carries no connotation of consciousness. It
is just the value of a signal. A perception may be related directly to
the current state of some property of the outer environment, but very
rarely is the connection so direct. The value of a perceptual signal
in most cases depends not only on the current state of the physical
variables that affect sense organs, but also on the current values of
other internal variables, which often depend on the history of the

The external variables that affect the value of a perceptual signal
might be very complex and context-dependent-such as those that
relate to the perception of the committment of one’s government to
democratic values-or they might be as simple as the rate at which
visible photons impinge on the retina, which relates to the perception
of brightness. Both perceptions, according to Perceptual Control
Theory, are just values of a signal, and neither need be conscious to
be effective. Whatever a perceptual signal depends on, each controlled
perception relates to something, simple of complex, in the outer
environment that can be influenced by the actions of the

Bringing a perception of some state to a desired (reference or goal)
value with which it is compared, and maintaining it there, is control
in the strict engineering sense of the word. The perception of
the external state is what is stabilized, not the external state
itself, and still less the action that the organism uses to influence
the external state-hence “Perceptual” Control Theory. For this
reason, PCT has a core tenet: “All behaviour is the control of
perception.” The actions that stabilize the perception may vary
dramatically as the environmental influences change, but a well
controlled perception varies only when its reference value

Not all perceptions can be controlled. Many, such as the perception of
the height of the sun in the sky, exist as signals that one’s
actions cannot influence. Other perceptual signals, such as of the
democratic commitment of the government, can be influenced only
slightly by one’s action. Yet others can be controlled with ease,
such as, for most people and animals, the perceived direction of gaze
of the eye.

Not only living things contain signal values. Inanimate objects such
as computers do, too. If those values are consequent on states of the
world outside the computer, they may legitimately be called
“perceptions” in the context of Perceptual Control Theory. If a
computer acts so as to maintain at a reference level some signal value
that corresponds to a state of the outer world, it is controlling a
perception, just as a living organism might do. This does not mean
that the computer is considered to be alive, but it does mean that the
analytic techniques applicable to control can be applied to the
relevant operations of the computer, just as they can to the relevant
processes of a living thing.

------------End of

The Darwinian answer to “why” is

Survival is the guiding principle of
evolution. Structures that survive are structures we still see around
us. PCT tells us why some structure survive – why we, and cats, and
trees, and jellyfish, and bacteria, do as we do.

Non-living structure tend to decay away
under the onslaughts of external energetic processes. Some, with
strong molecular bonds, or that are protected from external chemical
or physical disturbance, decay slowly. Others decay fast. But they all

Living things are different. They implement
negative feedback processes, using a flow-through of energy which they
convert from low-entropy form to high-entropy form (heat and waste).
And that goes for living things from the very first sustained chemical
feedback loop to the present day. It is negative feedback that keeps
certain values stable.

Some negative feedback incoporates actions
on the world outside the stable structure (a.k.a. “living
organism”). Those action reduce the effects of external
influences on the state of internal quantities. PCT (at least in part)
is about those feedback loops that work on and through the external
environment, In PCT, those quantities are called
“perceptions”, whether they be the level of chlorophyll in
the leaf of a tree, or the level of democracy one perceives in one’s
government. Of course, in a complex entity, there may be other
“perceptions” relating to internal states that participate
in feedback loops, and PCT is concerned with those, too. But they are
just assistive mechanisms to help the stabilization of the living
structure against the destructive energies of the outer

“Perceptual Control” is not a
mechanistic description of how we move. At least it’s not only that.
It is the whole reason we exist. Because of Perceptual Control, we are
individually able, for a while, to sustain our structure against the
buffeting of our environment – in other words, to build and maintain
an island of low entropy in a turbulent world. Evolution requires PCT,
since only structures that use Perceptual Control can survive the
world we live in.