[Martin Taylor 940727 16:00]
Bill Powers (940722.0510 MDT)
Martin Taylor (940721.1100)--
Multiplexing is just one kind of sequencing of control processes at
Is there another kind?
Yes, sequence control in general, controlling the order in which lower-
level perceptions are brought to different reference levels.
Multiplexing would be an example in which the sequence is closed and
That's a highly restrictive view of multiplexing. I don't think I've
heard multiplexing talked of in that way since the days of servo-controlled
Actually, multiplexing is not exactly the right word, because its
technical meaning has to do with using a single channel to pass several
interleaved signals, requiring synchronized demultiplexing at the other
end to sort them out again.
This is less restrictive, but still much more restricted than the general
use. If you leave off "requiring synchronized ..." and delete "interleaved"
you come closer. There are many ways of multiplexing, two extreme ones
being "Time Division Multiplexing," of which you describe one variety, and
"Frequency Division Multiplexing" in which the several independent signals
are sent in different frequency bands in the same channel.
I suspect that different disciplines may have slightly different precise
definitions for the term "Multiplexing," but they all come down to the one
that starts the article on the subject in the Encyclopedia of Computer
Science and Engineering: multiplexing, generally speaking, is the use of
a single facility to perform several independent but similar tasks. You
multiplex the use of your hand when you pick up a glass and later pick up
a book, or type a note... You multiplex the use of your retinal fovea
when you look at the screen to read this and then look at your garden to
see what just moved out there.
The example you use is a very good example of multiplexing:
A better image would be the performer
keeping n plates spinning on sticks or on a tabletop. The performer
stands back and keeps scanning over the plates, and when a plate is
moving too slowly, steps in and applies the control system that makes a
plate spin faster. There the same control system is used, but its point
of application is moved around as circumstances require. This requires
switching both where the action is applied and where the perceptions
come from. You can't be looking at one plate and spinning up another
one. Peripheral vision doesn't provide the required acuity.
Yes. Both input and output channels that link the control system to its
CEV are multiplexed. The effect as seen from the outer world observer is
that the control "facility" is multiplexed among the plates.
One key point about multiplexing is that if the "facility" is of a kind
to which the concept of information rate can be applied (such as a
communication channel) the total information rate of all the "independent
but similar tasks" can not exceed the capacity of the facility. (Please
note the "IF" in that sentence
Yes, that's what allows the whole multiplexing system to work, and why
alerting systems can be effective.
Were you paying attention to what you were saying "yes" to? The
coherence of large parts of the perceptual field is the basis of my
argument that there are far fewer (by a factor of 10^3) input degrees of
freedom than there appear to be on the basis of counting sensory endings
(or optic-nerve fibers).
Yes, I WAS paying attention to what I was saying "Yes" to, and I STILL agree
with it. You can't force me into an argument with you on this point. It
is fundamental to my position, and is irrelevant to the issue that started
this whole thread--the degrees of freedom argument that leads directly from
PCT to the need for an alerting process. What we agree on is a statement
that the human organism is capable of controlling those perceptions that
affect survival at a rate sufficient to handle the disturbances (normally)
encountered in those perceptions. That leads to the truth of what you say:
My contention is still that the input and output degrees of freedom are
fairly well matched.
If "what I say three times is true," will you accept the truth of my
statement that I agree with you on all the above (below the ========= line)?
I think I've said it three times now, but I'm prepared to say it another
seven times, if that will bring the total to three
Could we then proceed (after the CSG meeting) to discuss the issue of
degrees of freedom WITHIN the sensory and output systems, and the requirement
it imposes for multiplexing (some of which involves alerting, on the
My general argument against the concept of "alerting" is that this is
simply an ordinary control process viewed at too low a level. It's akin
to the behavioral illusion in which disturbances appear to be stimuli
that cause responses.
If we could confine the discussion to an enquiry into the truth of this
statement, I would be very happy. You may be right, but the argument to
date has clouded any attempt to investigate the issue. My belief is that
there is an analogy between the two situations, but that the analogy
misleads. I could be wrong.