Newsgroups: bit.listserv.csg-l
Date:         Wed, 19 Aug 1992 12:30:35 EST
From:         Avery Andrews <andaling@FAC.ANU.EDU.AU>
X-To:         csg-l@vmd.cso.uiuc.edu

[Avery Andrews 9108191231]


(penni sibun 920818.1200)

  >maybe someone can explain this to me.  when you say ``signal'' or
  >``variable'' or ``percept'', it has connotations to me of a unified
  >thing, like a tone, or a light intensity.  but when i look at the
  >road, i am not perceiving something like a tone.  if you can explain
  >how all the stuff my eyes take in can be a single unified thing, maybe
  >i won't find it so oversimplified.

With a sonja-like visual system, one might set one marker to tracking
the hood-ornament, another the center line of the road, & let the controlled
perception be the distance between them (or so I guess--having never
built a sonja-like visual system, I don't have full faith in my
intuitions about them).

On the general subject of the supportiveness of the environment, I
suspect that the difference between PCT & c&a-style interactionism
might be more one of rhetorical emphasis than substance.  PCT in
fact depends very much on the fact that many (in fact most, by an
overwhelmingly large margin) features of the environment can  be
leaned on.  A steering subsystem would for example depend on all sorts
of facts about roads and carparts about which it knows nothing, as
well as upon the workings of the lower-level control-systems it
works through.  To perform at a minimal level, all that it has to `know'
is the relationship between change in torque-applied-to-the-wheel to change in
relationship-between-hood-ornament-and-centerline-markers (of course,
for hi performance, lots more is needed, but the extra knowledge isn't
about car parts, etc.).

One theme of c&a interactionism, as I hear it so far, is that you
don't have to know very much to get by --  keeping your eye on the
situation and following a few simple rules is enough.  PCT claims that
you can say a bit (or maybe a lot) more than that, in particular,
something about the general nature of the kinds of rules that will in
fact suffice to get you by -- that on the whole, they tend to be such
as to keep perceptions ( = the output of `registrars') at particular
values, or at least within particular ranges of values.  The claim is
that architectures that don't do this won't work.  I would take this
claim to be decisively refuted if someone built a robot vehicle that
did stay on the road in an interactionist manner, but just because it
was `the easiest thing to do', without containing anything remotely
like a control system controlling a perception along the lines of
`position-of-vehicle-relative-to-the-road'.


It remains to be seen if this is a `golden thread' that will be the
indispensible key for untangling or building these systems, or if it is just
one of a dozen rules of thumb for doing so.  It does so far seem to me
to be a useful organizing principle that is absent from c&a (but for all
I know, this could be only because they think it's so obvious that it
isn't worth mentioning).  And it also remains to be seen if, when
applied complex systems, it will apply cleanly, or instead grow so much
hair that it will get difficult to discern the original beat under the
fuzz.

For example, whatabout the little positive feedback loop in the
beerbug's feeding controller (based on the supposed wiring of the
infamous Aplysia).  What goes on here is that if the bug is hungry
enough (the energy level is far off enough from its reference level)
and over food, it will start eating, but being eating also excites
the feeding controller, so it keeps eating even when its energy level
is no longer low enough to successfully trigger eating.  The whole
system can be regarded as (part of) a control system for the maintenance
of energy-level, but the positive feedback loop looks like at odd bit
stuck in.


Avery.Andrews@anu.edu.au
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU