[From Bill Powers (940722.0510 MDT)]
The shuttle landing was waved off until tomorrow because of weather, so
I didn't need to be awake this early.
···
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Martin Taylor (940721.1100)--
Multiplexing is just one kind of sequencing of control processes at
lower levels.
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
repetitive. Poking the buttons on a telephone would be a finite sequence
in which reference signals for poking are repetitively varied while
another sequence control system selects the target positions to be poked
in the right order. Playing a melody on a flute involves still another
kind of sequence control, where different values of the same perception
(pitch) are produced in a specific order, with no switching of reference
signals to different control systems.
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. 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.
... if you would like me to send publicly the response I was preparing
for private communication, I will. It includes some small quotes from
your private message, to which I hope you will not object.
Fine.
The main limitation on input degrees of freedom is not the number of
individual sensory nerve endings we have; it is the fact that large
parts of any perceptual field are constrained to change in a coherent
way because of the coherence of objects; even the objects are
constrained to behave in specific relationships to each other because
of the nature of the external world.
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). If something constrains large numbers of neural
signals to vary in a related way, those neural signals are no longer
independent and don't count as separate degrees of freedom. They are
just redundant measures of the same thing. The environment is the
bottleneck; in any process involving a series of processes, the process
with the fewest degrees of freedom sets the limit for the whole series.
This applies inside the nervous system too (to reveal another arrow in
my quiver). The firing of nerves may seem to provide a very large number
of degrees of freedom per second, but the response of analog chemical
processes inside receiving cell bodies has a much smaller bandwidth than
would be calculated from the duration of a neural spike. There goes
another factor of 10 at least.
My contention is still that the input and output degrees of freedom are
fairly well matched.
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.
Yes, indeed. I see no issue here. The example you use of shifting
your gaze position in order to update your perception of the state of a
different chunk of the real world is a good one. It covers the two
modes I called "search" and "explore."
It also further reduces, by a large factor, the degrees of freedom per
second of the perceived world. Also, do we really want to start
classifying behaviors as the basis for a model? Down that road lies a
proliferation of entities that knows no end. Searching and exploring
are, no doubt, behaviors, and it's a good thing to bring up familiar
patterns of behavior to be explained by the model. But no additional
properties of the model are needed to explain them. Perhaps you bring up
these subjects because they may throw some light on the kinds of
underlying operations the higher control systems must be able to
perform. What we recognize as searching and exploring are _outcomes_ of
using certain operations in a certain way. They aren't basic modes of
operation.
If nothing happens when an uncontrolled perception changes, then there
is no reason for that perception even to exist.
This is a most important comment. It is at the core of J.G.Taylor's
theory, and I have believed it for more than 30 years.
That's too bad. Anything you have not doubted for more than 30 years is
far overdue for some serious skepticism. I doubt PCT about once a month,
and have to reconstruct it from scratch. Got to keep those premises
aired out or they get moldy.
I question whether your concept of "alerting" came from a
consideration of degrees of freedom. I suggest that it existed long
before you ever had such thoughts.
Perhaps. That's a question of historical record. As a consequence of
your comment I have just reread my 1972 paper in which I introduced the
concept in the form I now use it, and I find that I did use a degrees
of freedom argument then ...
But which came first, a belief that there was a real phenomenon called
"alerting" or the degrees-of-freedom explanation of it? I think that the
concept of alerting was around for a long time before 1972.
As I have said before, I think of it as one of those many places where
PCT makes beautifully clear something that was separately described,
unexplained, and somewhat vague beforehand. What has puzzled me is why
this fact has causes so much disturbance to the PCT old hands.
PCT can be used, with proper introduction of extraneous concepts, to
justify belief in any phenomenon, particular if the phenomenon was
vaguely defined to begin with. "Alerting stimuli" are a holdover from
the days when it was believed that events in the environment had
inherent values for organisms and could "trigger off" or "facilitate"
(lovely dormitive terms) appropriate (another one) responses (and
another). With that belief in the background, it was easy to see that
certain events which were followed by responses to other stimuli must
have alerted the organism to the presence of the other stimuli,
preparing the organism to act in the right way, or more quickly. This is
a plausible explanation, given the underlying beliefs.
But what if that is a complete misinterpretation of what is going on?
Suppose that so-called alerting stimuli are simply disturbances of some
higher-level controlled variable, which are counteracted by actions that
alter other perceptions which contribute to the state of the same
controlled variable? Now what formerly seemed to be a special class of
"alerting" events is absorbed into the general concept of a disturbance,
and no longer needs to be thought of as a separate phenomenon.
We should be glad to get rid of concepts like "alerting." Such concepts
simply increase the number of apparently different phenomena with which
we must deal. What we need is to reduce the number of different
phenomena to make the task of understanding behavior simpler. If
alerting is simply a form of disturbance, then we don't have to carry
along an extra concept in our heads; the idea of a disturbance includes
the same phenomenon, as well as many others. We aren't throwing away any
data; we're just viewing the data through a more efficient ordering
scheme.
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Paul George (940721.1100)--
However note that even control engineers do not view that which is
being corrected as that which is being controlled. From _their point of
view_ the controller is controling the process, i.e. trying to control
the environment.
I am beginning to think that this is how _naive_ engineers view the
process. Of course their task is to be sure that the environment is
controlled, because that is what the customer wants. But the control
system itself, the one they build and that must operate on its own, can
control only what it perceives of the environment. If the perceptual
system is set up to perceive the wrong thing, the engineer may believe
that the environment is being properly controlled, when in fact the
control system is controlling some other aspects of it which only
happens, for now, to keep the variables the engineer is interested in
within the required limits. But a change in circumstances can leave the
control system controlling quite successfully while the environment goes
to pot.
Suppose the engineer wants to control the temperature of a bath. He
gives the control system a thermocouple to register the temperature,
constructs the rest of the loop, and all is well. But the thermocouple,
as it happens, is sensitive to radiated energy as well as conducted
energy. During the tests, it happened to be shielded from radiated
energy, or there were no radiant energy sources to worry about. So
everything worked. But when the control system is moved into the factory
where there are powerful lights overhead, or sunlight coming in through
windows, it will start controlling for the sum of the input energies
from ALL sources, not just the intended one. When the lights go on, the
temperature in the controlled bath will go down!
Worse yet, when the engineer is summoned to see this problem, he goes
right up to the bath and stands there, and sees that everything is
operating normally. When he goes away, removing his shadow from the
thermocouple, down goes the bath temperature again.
Engineers may intend to control variables in the environment, but the
control systems they build can control only their own sensory signals --
no matter how the engineers think about it. Smart engineers know this,
if only intuitively; this is why they specify periodic calibrations of
the sensors. When a sensor drifts in calibration, the control system
continues to hold the sensor's output signal at the set point, but this
results in the external variable's changing. This is why they make sure
that a sensor which nominally senses one variable, like light intensity,
is not also affected by other variables, such as magnetic fields or
temperature or humidity.
A control system controls its own sensory signal. This is not a matter
of interpretation; it's how control works.
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P.S. I've adjusted my format a little (trying to get rid of form-feed
characters for my own reasons). Should be only short blank spaces.
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Best to all,
Bill P.