Newsgroups: bit.listserv.csg-l
Date:         Fri, 18 Dec 1992 15:52:13 EST
From:         mmt@BEN.DCIEM.DND.CA
Subject: Re: Memory in the model

[Martin Taylor 921218 15:30]
(Bill Powers 921218.1030)

I have a problem with the specific detail of Bill's proposal.  Not with
the principle.

>There is one version of the HPCT model that we have tossed around
>for some time without really deciding about it, in which the
>world we experience is ALWAYS the modeled world, PLUS whatever
>error comes from lower systems. It works like this:
>
>                            |
>                         ref|sig
>                            |
>             --percept-->COMPARE-->error--
>            |                             |
>            |                             |
>         INPUT FUNC                  OUTPUT FUNC
>          |   -|                          |
>          |     ------- MODEL ------------
>          | ->correction-/                |
>          |                              /
>        **P**          **R**--<---------             (P and R added by MMT)
>          |              |
>          |           ref|sig
>          |              |
>           \ --error<--COMP<--percept<----
>            |                             |
>            |                             |
>
>
>The bottom system is mirror-reversed to avoid crossing signals.
>
>The higher system controls a perception made of the sum of a
>MODEL output and the lower-level error signal.
>
>The basic idea is that when the higher system acts to control the
>model, its output enters both the model and the lower systems (as
>reference signals). If the lower systems succeed in bringing
>their individual perceptual signals to the demanded reference  level,
>they will send no error signals to the higher system. That
>means that the model works; the outputs that control it have the
>correct effects when also used as reference signals for the lower
>systems.

This seems to work when there is a one-to-one relationship between lower
and higher systems, but will it work with many-to-many?  The reference
signal in the lower ECS is not the output from the higher, but a function
of a vector of such outputs from higher ECSs.  So when the lower perceptual
signal matches its reference, the perceptual signal returned may well be
quite different from the output that is sent (Points R and P that I added
to Bill's diagram.  Likewise the perceptual signal in the higher ECS is
a function of a vector of signals like P from many lower ECSs.

If all the lower error signals are zero, then the higher one will presumably
also be zero, but the reverse is not true.  The higher ECS can have a zero
error when none of the lower ones are satisfied.  I'm not sure what this
would do to the correction aspect of the memory module.  Should there be
a correction or not?

And what evokes a specific memory?  In the BCP diagram, we mentally inserted
"reference vector" as an addressing code for a scalar memory output--a
table lookup function.  That seems reasonable, but we were not at all clear
how it would or could work.  And in the context of the planning exercise
that I described the other day (shopping robots in the supermarket), we
could not see how to incorporate the real-world constraints presented
verbally and never before experienced by any ECS operating through a real
world CEV.  That question, also, still hangs in the air.

Basically, I like the concept that the ECS deals mostly with model predictions,
corrected by error.  But I'm not sure what error, or what is the memory.
Is it a vector of sensory inputs, to be corrected by the vector of incoming
error signals (or more probably the incoming perceptual signals--more robust)?
And what evokes one memory rather than another?

Remember my point about the reduction of information rate as we go up the
hierarchy.  It is this that gives play to predictive memory models.

Martin
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU