Newsgroups: bit.listserv.csg-l
Date:         Fri, 20 Nov 1992 12:02:16 EST
From:         mmt@BEN.DCIEM.DND.CA
Subject: Re: association & g-ma neurons

[Martin Taylor 921120 11:30]
(Avery Andrews 921120.1145)

>The idea is that whenever the pain wire fires, something happens inside
>the black box such that, subsequently, the closer the sense-vector gets
>to what it was when the pain wire fired, the larger a signal comes out
>along the fear wire.  This signal then is then handled in such a way
>is to typically induce behavior that will alter the sense-vector.  (If
>the organisms motor system is e-coli style, the fear signal would
>contribute additively to the tumbling rate).
>
>Stick a lot of these things together in the right way, & you might be
>able to get a fast associative learner with no grandmother neurons.

This looks to me so much like Bill's reorganization of the perceptual
input function that I can't tell the difference.  I had originally thought
that Bill was applying reorganization only to the output links among ECSs,
but some time ago he mentioned experiments he had been carrying out on
e-coli type modification of the perceptual input function as well.  And
since "pain" would not be an input to the ECS that is reorganizing, but
might be a kind of perceptual consequence of an error in a critical (intrinsic)
variable, the line you have labelled "pain" would actually be a reorganization
signal that occurred because of the intrinsic error, rather than the pain
perception itself.

But yes, there would be lots of those things, and, I claim, no need for a
"grandmother cell" to control all the many perceptual attributes of
grandmother.  The only necessity in the hierarchic control system is that
there be ECSs that control perceptual signals whose control happens to be
effective in maintaining critical variables near their reference levels.
The more complex the living control system, the more adaptable it is, by
virtue (speculation mode) of being able to control perceptual signals that
correspond to more complex CEVs in the real world.
------------------
(Bill Powers--whose send script doesn't yet include a date stamp--921119 1640)

>An ECS _can_ be represented by a single neuron, but I don't know of
>any examples where it _is_. The simplest control systems I know
>about, the spinal reflexes, involve one neuron for a sensor, one
>neuron for a comparator (the spinal motor neuron) and a muscle for
>an effector.

There's a critical point about this particular identifiable control system,
and that is that its peripheral components are not ECSs.  What I mean is that
the sensor neuron is essentially different from the final neuron that activates
a mechanical muscle, and therefore the lowest level ECS that connects
peripheral sensors with muscular actions MUST have at least two neurons.
As you say, it actually seems to have three.

But when you get deeper into the system, the outputs from any ECS could
come from the same neuron that receives the inputs to it, meaning that the
whole ECS could be in one neuron.  Since we do not (so far as I am aware)
know of any physiologically identified hiegher-level ECSs, I don't see where
there is evidence one way or the other that the smallest unit that acts as
an ECS is smaller or larger than a neuron.  But the smaller the unit, the
weaker the numbers argument against gransmother "cells" (really ECSs).

>Furthermore, as in the interchange with Oded today,
>these simple control systems operate in parallel bundles so the
>effective control system probably involves dozens to hundreds of
>neurons, plus the muscle fibers.

This I do agree with.  It's part of the foundation of my arguments about
what we might call "subsymbolic PCT" if the word "symbol" didn't have an
unfortunately double meaning as a percept and as an analytic concept in PCT.
These dozens to hundreds of overlapping outputs (and inputs) are unlikely
to form strictly isolated modular groups, but are more likely to be interwoven
and to blend into each other.  Just as control of a low-level percept is
effected by a separated muscular output, and as control of intrinsic variables
(in your model) is effected by separated control of apparently irrelevant
perceptual signals, so may the "core" percepts in a modular bundle be partly
controlled by actions of peripheral members of the bundle.

Martin
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