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Date:         Mon, 5 Oct 1992 18:10:54 -0600
From:         "William T. Powers" <POWERS_W%FLC@VAXF.COLORADO.EDU>
Subject:      Reorganization; tracking; Hebb; competing behaviors

[From Bill Powers (921005.1330)]

Greg Williams (921005) --

What I'm being so stubborn and obtuse about (I can see how it looks
from your end) is really simple: I see learning as a skill of an
organism. A rock does not learn, no matter how long you try to teach
it or how you disturb it. The mechanisms of learning -- those that
decide when it is necessary to learn, those that decide when learning
has been successful, and those that actually create changes of neural
connections and synaptic weightings -- belong exclusively to the
organism. There is nothing the outside world can do to make these
MECHANISMS work any differently. This is just like saying that the
mechanisms of muscle contraction are properties of the organism that
no outside environment can change: muscles contract in response to
driving signals because of their biological construction, not because
of the world in which such contractions take place. So it is with
learning: learning is a function of a biological system with the
necessary equipment.

The kernel of this "necessary equipment" is what I call the
reorganizing system. This system represents a built-in skill of the
organism; it works according to its inherited design, over which the
outside world has no control, and on which neither the outside world
nor the inside world has even any influence.

The argument we're having is failing to converge because we're talking
about two different things. What I'm talking about is the fundamental
organization of the organism; what you're talking about is how this
organization interacts with particular external events and processes.
I'm talking about how a muscle works; you're talking about what that
muscle will do under various kinds of driving signals.

Because of the built-in capacity to reorganize, and the built-in
criteria that go with it, this particular piece of equipment has an
especially important function: it makes the organism (the human one,
at least) infinitely adaptable to external circumstances. From the
standpoint of the organism, IT DOES NOT MATTER what particular control
processes have to be learned. The organism has no built-in preference
for controlling any specific variable in any particular way -- not,
that is, among those variables controlled by the learned part of the
organization. The only unchangeable requirement is that the critical
variables be maintained near their respective reference levels. The
world outside the organism has absolutely no influence on that
requirement; it is absolute. Critical reference levels are the only
ones in the organism about which we CANNOT say that they are set as
they are in order to accomplish something else (during one organism's
lifetime).

"Mundane learning" works because of critical error. All learning does,
that involves a change in any functions. Of course there are also
other processes having nothing to do with reorganization that are
called learning: executing systematic search patterns, memorizing
facts, memorizing and imitating sequences of actions, executing
program-like algorithms that employ present-time information from
outside the organism, and so on. Those are either memory phenomena, or
are themselves learned control processes acquired initially through
reorganization.

My point is not that organisms have no influences on each others'
behavior, or even that these influences can't be manipulated to have
intended effects. It is that these are all surface phenomena, acquired
through the control actions of a reorganizing system. Each organism,
as suggested today by "von", simply controls for its own perceptions,
fending off any external influences that don't produce effects it
already wants. This applies to manipulators just as much as to the
manipulated; a manipulator is just trying to make the world look the
way the manipulator wants it.

I am also not rejecting the idea of interaction. Organisms can ask for
help (in numerous ways), and get it. They will reject the very same
"help" if it is given without being requested. Organisms can ask for
instruction and information, and get it. They will reject the same
instructions and information if it was not requested -- provided they
are given any choice in the matter. The demand for learning comes from
inside the organism, not from outside it. There is no such thing as
"teaching" as a transitive verb. All you can do it make it possible,
or necessary, to learn. It isn't the teacher who guides the learner,
but vice versa.

Ah, well. We've run this subject into the ground for now.
--------------------------------------------------------------------
Marcos Rodregues (921005) --

I take it that you want to track the light on the moving arm in order
to obtain a record of the movements. Just how automatic a project do
you want this to be? If you want a device that will optically track
the light and put out signals that indicate its position in two or
three dimensions, this could become quite a project.

Here's an illustration:

Let the light be a photodiode modulated at, say, 1000 Hz. To detect
its position you need to form an image of it with a lens in a small
telescope, focused on a cluster of 4 photocells, two for the x
direction and two for the y direction. The photocell signals go
through an AC amplifier and phase-sensitive detectors synchronized
with the 1000 Hz signal that modulates the photodiode. This eliminates
ambient light. Each pair of photocell signals enters a differential
amplifier that yields a position error signal. The position error
signals for x and y become reference signals for servos that move the
telescope in x and y. Thus the telescope is always aimed so that the
pairs of photocells are illuminated equally. The servo feedback
signals are used as the indicators of position. As the arm moves, the
servos make the telecope track the light. If you want depth
information you have to use two telescopes. A-to-D converters will
sample the servo feedback signals, and from the geometry you can
calculate the actual x-y (-z) position of the light.

This can also be done more cheaply. Build a frame with three degrees
of freedom that is pivoted at the shoulder and at the elbow. Strap the
frame to the arm. Put linear potentiometers on each pivot. Put
voltages on the pots, connect their outputs to 3 A/D converters, and
let the computer calculate the arm segment configuration.

To do this off a video tape, you can put an electronic gate on the
position of the light. The gate would be divided into four regions,
and the video signal within each region would act like the signals
from the photocells. The gate would be moved (in time-delays) instead
of moving the telescope; otherwise the principle is the same. But
again, not a simple project.
-------------------------------------------------------------------
Gary Cziko (921005.0313 GMT) --

>P.S.  Perhaps Bill can let us know what he found out about the
>possibilty of modifying STELLA so that real-time data can be used.

So far I haven't heard back from Hammond.
-------------------------------------------------------------------
Martin Taylor (921005.0730) --

That was a nice summing-up of the basic HPCT architecture. I think
that all of the candidates for reorganization are valid. Some, such as
the linkages from one level to another, may be most actively
reorganized during development (I think we learn new perceptual
organizations at a decreasing rate later in life). Also large-scale
changes in linkages of all kinds probably decrease in frequency
(during development, neurotaxis seems very important; this is a more
drastic way of making new connections than merely altering the weights
of synaptic connections).

My main difficulty with Hebbian learning is that it seems unmotivated;
that is, it's so local that I don't see how it could be related to
critical variables. The only test of it that I know about, in terms of
modeling, was done by a graduate student in Harry Klopf's lab at
Wright-Patterson Air Force base; to keep all the weights from going to
maximum or zero, all sorts of kludges had to be introduced. The basic
model by itself didn't work. Maybe others have made it work better
since then.

>This is indeed one form of Hebbian learning, but the motivation is
>not to get away from a teacher, so much as to provide the maximum
>discrimination among input signals that is consistent with the
>variation in stimulus patterns. Usually, weights on low-valued
>inputs decrease when weights on high-valued ones increase, so as to
>sharpen the discrimination.

So this is a "normalized" model? That would partly take care of the
problem of making some weights decrease. I think a workable version of
Hebbian learning would have to be pretty far advanced over the
original notion of just "increasing the strength" of connections.
----------------------------------
I still don't understand the mechanism by which competing behaviors
prevent each other from happening outside the organism. Just saying
that a behavior has a "low impedance" doesn't explain much. You still
leave some of the systems with unsatisfied errors inside the organism,
meaning very large outputs. Why aren't those large outputs producing
large efforts?

>I have been taking the position that each ECS is blind, in that all
>it knows is that it provides an output when it has a non-zero
>error.

So have I.

>If the hierarchy has been effectively reorganized, that
>output will reduce the error more probably than not (whether it
>actually does is dependent on the momentary state and disturbances
>of the world and on other control systems that affect components of
>its feedback circuit, but the ECS knows nothing of that).

I don't see what "probably" has to do with it. The only way for an
error to be small is for the output to be in the state that brings the
perceptual signal nearly into a match with the reference signal and
keeps it there. If there's any uncertainty about whether the error has
been reduced, you're going to have a very low-gain control system,
incapable of opposing disturbances to any interesting degree.

>You seem to require the ECS to know what lower-level ECSs are doing
>and to choose which one to activate.  I will turn back on you your
>own frequent question.  What percept does it control to do that?

The higher one knows a perception derived from copies of the lower
perceptions (plus, in general, some uncontrolled perceptions). A
system that acts by selecting which lower level action to perform will
cease to look for an effective choice as soon as the first one is
found that corrects its error. This would be at least a category
control system, where selection might be in terms of the name of the
class of perceptions. Should I take the "bicycle" (quick check for a
perception in that category) or (failing that) a "car?" (something in
that category is found and the reference level is satisfied). This
implies a priority sequence. Another way would be simply to look for
something in the class "transportation." Then the search wouldn't be
prioritized. If you happen to spot the roller skates first, that ends
the search. When any suitable perception is found, the error is zero
and the scan ceases. It is then up to other systems to do something
with the "bicycle" thing or the "car" thing that has been spotted:
drive it away, wash it, sell it, paint it.
-----------------------------------------------------------------
Best

Bill P.
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU