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Date:         Thu, 19 Nov 1992 11:06:08 -0700
From:         "William T. Powers" <POWERS_W%FLC@VAXF.COLORADO.EDU>
Subject:      Images,Dag's rewrite,virtual signals

[From Bill Powers (921119.1000)]

Misc public replies to private posts:

Martin, a purchase order for the Little Man v.2 will be fine.
A Macintish port of my demos by your people would be quite possible.
Only library references would need changing. Will work with you as
required.

Bruce, I would appreciate it if you could follow through on the neural
net chip.
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Rick Marken (921118.1300) --
It is important for a loose canon not to fire when pointing inboard.
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Avery Andrews (921119.1136)--

On images:

The power of the pandemonium-type model really shows up when you talk
about things like reference images. Neither a perception or a reference
level having to do with an image needs to be a literal image (bitmap).
The reference signal signals THAT the relevant dimension is present, and
how much of it. To recall an image for perception via action or
imagination one need only supply a nonzero scalar reference signal to
the right control system. If lower-level systems are involved, you get
the lower-order details of the image on the way to producing the "image-
is-present" signal. If the imagination connection is short-circuited at
the top level in question, you get the "image-is-present" signal without
any corrorobating details such as the image itself. You remember THAT
the image was there, but you don't experience the image in terms of
sensations, configurations, etc. How complete an image you get depends
on how many dimensions of the perception you specify -- i.e., how many
top-level control systems you send scalar reference signals to. How
vivid the image depends on the level at which the imagination-connection
is closed.
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Dag Forssell (921118.23.00)--

Your rewrite captured exactly the tone I was hoping for. Very, very
good! Suddenly the whole document, including the parts you didn't
change, looks much better. As far as I'm concerned we can go with it.

I really admire your ability to act constructively on criticism. I even
respect your opinion when you say I'm nuts (although I already knew
that).
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Oded Maler (921119)--

>Now consider a different situation where those two signals are not
>combined to create a new perceptual function which is servoed, but
>rather are both servoed independently but their effects are
>combined via the output function (e.g., two nerve fibers that feed
>into neighboring parts of the same muscle).
You're right about this. An excellent and even more extreme example is
any of the so-called spinal "reflexes." The tendon reflex involves
dozens or maybe hundreds of control systems acting in parallel, all
their output signals contributing to the tension in a single muscle.
When the muscle tenses, all the feedback signals rise at once. The net
reference signal, averaged over all the comparators, leads to a set of
error signals which again rise and fall together. The error signals
enter the muscle, each one causing a different set of fibers to
contract. All these effects finally come together into one single muscle
tension that stretches the tendon. I spoke of this effect in BCP.

>In such a situation, there exist virtually a combined signal which
>can behave as-if it is the controlled signal, but it does not
>really exist inside the system.

Yes, we can represent all these parallel control systems as a single
equivalent system containing single scalar signals. This is not a
"complex" of signals like what Martin Taylor is talking about, because
the effective signal is simply the sum of all the signals of the same
kind (or something like it). Different patterns of signal intensity
within each bundle of signals do not have any significance as far as the
controlled variable or the action is concerned -- changing the
distribution of signals within a bundle would not change the outcome if
the sum were preserved.

>Put it another way, the "real" signals can be probed directly (in
>principle) by an external observer, but in order to observe the
>"virtual" signals, the measurement instruments of the observer >should
also include the missing circuits for creating the >combinations.

Yes. In a way you're saying what I'm about to say to Martin in the next
comment. You're pointing out that in order for the virtual signals to be
known, the measuring instrument must contain a perceptual function that
makes the virtual situation real by creating a meter reading. I'm saying
that for the brain to make use of virtual signals it must do the same
thing.
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Martin Taylor (921118.1130) --

>Please note that I am remaining agnostic as to whether complexes as
>such have reality outside the mind of the analyst, or whether the
>higher ECSs that convert them to scalar perceptual signals are
>actually necessary.

I count agnosticism as progress.

My point is that a complex is not a unitary thing until it has passed
through a perceptual function that determines what kind of unitary thing
is there. If such a complex has reality in the mind of the analyst, that
is evidence that the analyst has a perceptual function of the kind
required to see it. If a human analyst can see unity in such a complex,
then the model needs to have the ability to do the same thing. If the
complex is left unperceived by this sort of function -- that is, if it
is not represented by a scalar signal -- then it is just a collection.
The difference is like that between a chemical mixture and a chemical
compound -- except that something else has to do the compounding.
None of this argues against complex perceptual functions in which
signals interact before the final scalar outputs are produced. A set of
perceptual functions could look like a perceptron, with all kinds of
interal interactions, combinations, and feedbacks. But coming out of
this perceptron will be individual output lines, each carrying a scalar
signal that is a different function of the inputs to the perceptron.
Each output line could then be represented as the output of a separate
perceptual function, so the perceptron would be conceptually converted
to a collection of input functions that all receive copies of the same
set of inputs and independently compute their output perceptual signals.
As I've said before, that's a convenient fiction, and we can't explain
in that way how the perceptron actually works. The perceptron is the
physically real organization. My representation just makes it easier to
understand once it's organized.

By the way, has anyone ever thought of putting a constraint on a
perceptron such that all its possible output signals are orthogonally
related to the set of inputs? This would be extremely handy if we want
one perceptron with multiple outputs to be part of a set of independent
control systems, each controlling one of the perceptual outputs.

If I haven't made my mental image clear, what I'm thinking of is that a
perceptron really represents a GROUP of input functions.
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Best to all,

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