[From Bill Powers (950303.0945 MST)]
Martin Taylor (950302.1300)--
I take "perception" to represent the output of a perceptual
function. But "perception of" is something else again.
"Perception of" is an assertion by an an outside agent (i.e.
another perceptual system, whether in the same hierarchy or
another) whose input is not only the perceptual signal, but also
some aspect of the "real" world. "Perception of" is a statement
that some perceptual signal correlates with some other perception
of the real world.
This is a very clear statement of the problem. The problem is
exacerbated when the two people think they are talking about the same
thing in the external world, and don't realize that there is an
undefined term:
Given: Your perception of X
My perception of X
Then: Your perception corresponds to my perception.
Our perceptions correspond to X (where X is still undefined).
... if I happen to have in my hierarchy a PIF that gives a strong
output in the presence of rotten apples, but not of rotten grapes,
I claim that I truly perceive a rotten apple--whether or not it is
a scented plastic imitation. The facts of the real world are never
known to me, but my perceptions may change when new sensory data
come available. What I perceive NOW is truly what I perceive.
When you have a PIF (perceptual input function) that reports the
presence of a rotten apple smell, there is no need to infer or imagine
its presence. This observation is infallible -- unless you go on to
claim that the apple would indeed prove to be brown and mushy inside if
you opened it up. THAT would be an inference. If there is no other apple
nearby, the inference might prove out 99.9% of the time, but the claim
would still be an inference, not an observation, a perception.
But a process that says "I perceive red. I perceive round. I
perceive dark small line protruding from round... Therefore I have
an apple" is quite different from perceiving an apple.
Exactly what I was getting at. You put the problem as succinctly as
possible in saying that it is represented by "perception of ...". This
very common usage begs the question (meaning that the statement or
question assumes without proof the very issue being stated or
questioned, as in "Have you stopped beating your wife?"). Discussions of
epistemology are constantly running afoul of this logical shoal. "When
you see an apple, is the apple really there?" The only proper answer is
another question: "What apple are you talking about?"
One of my favorite diagrams concerning perception is the one that shows
a right-side-up vertical arrow in the environment, an upside-down image
of it on the retina (with optical rays connecting the appropriate
points), and a pathway into the brain where the same arrow is again
shown. The naivete is charming. The same diagram, of course, applies to
us as we view the diagram, and so on forever.
Anyway, have you also considered this subject as it applies to
"information about ..."?
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Bruce Abbott (950302.1600 EST)--
We operant guys would say that the two responses, keypecking and
turning, are both under "stimulus control," meaning that the
probability of observing each response depends on which stimulus
(red or green) is currently present. What controlled variable is
being disturbed? Why does behavior change when the "discriminative
stimulus" changes?
I think we need to take these questions seriously. We have never tried
to model the situation where one perception appears to work as a signal
rather than as a controlled variable in itself. It's possible, of
course, that this interpretation of the role of the perception is
misleading, but we need to find the "correct" description and show that
it makes at least as much intuitive sense. The problem is similar to
that of showing that some "stimuli" should really be interpreted as
disturbances. Once you can see exactly what is disturbed, and how the
control action counteracts the disturbance and _appears_ to be caused by
the stimulus, the PCT interpretation becomes at least as believable as
the other one. We need to do this for the case of "discriminative
stimuli" or else admit that some stimuli serve as triggers for other
control processes.
I didn't say that it would be particularly difficult to develop a
coherent PCT account of these phenomena, only that it needs to be
done and that I'm starting to think about it. I'd certainly
welcome your insights.
Probably the most direct solution is the one Rick Marken suggests:
consider that there is control of a logical condition:
p = (Red AND peck) OR (Green AND turn-in-circle)
r = TRUE
There are two contributing lower-order perceptions under the organism's
control (peck, turn-in-circle) and two that are independently variable
(Red, Green). As I interpret the description, there are two additional
relationships imposed by the environment: red XOR green is true, meaning
that the light is either green or red but never both, and peck XOR turn-
in-circle is true, meaning it is physically impossible to do both at
once.
We can investigate our guess about the nature of the controlled
perception by trying the various combinations of disturbances and seeing
if the behavior always changes to keep the perception defined above
matching the assumed reference condition, TRUE. For example, we could
turn one light blue, which is neither red nor green, which would make
the perception FALSE no matter what pattern of behavior the organism
controlled. This should lead to anomalous behavior, perhaps switching
back and forth between the two behavior patterns; this behavior would
cease only after a long time because there is a permanent error signal.
On the other hand, we could turn both lights on at once. This makes the
proposition TRUE no matter which behavior pattern is selected, so we
might expect one pattern to be picked at random, after which it would be
maintained because there is no error to produce another switch.
Of course there are many other possibilities to investigate. Is a green
light equal to not-red? Or does not-red mean that the light is off?
There are other possible logical perceptual functions: for example,
logical implication may be involved, as in "It is not the case that A is
true and B is false." Logical implications have their own peculiarities:
if A implies B, the proposition is false ONLY if A is true and B is
false. All other combinations leave the implication TRUE -- even A false
and B false.
The only way to find out what logical function (if any that we can
understand using Boolean algebra) describes the perceptual function is
to test various hypotheses -- the good old Test again. The actual
behavior involved, pecking or turning in a circle, is of little interest
in itself, however striking it may be to the experimenter. What we would
be investigating would be the logical function of perceptual variables
that is under control by the organism.
To do this it is also necessary to look carefully at the logic of the
experiment. What is the contingency for the case when both lights are
on, or both off, or when a light of a new color is shown? If the animal
turns in circles, pecking at the key once each time around, what is the
contingency? It's very easy to set up the logic of an experiment with a
particular set of relationships in mind, and forget that you have to
cover all combinations of true and false, not just the ones you first
thought of. Bill Leach will no doubt support this observation;
forgetting to cover all logical possibilities is a pitfall of electronic
logic design. Whichever condition you forgot to provide for is almost
certain to be the next one that occurs.
I can easily write a simulation that switches control systems in
response to changing input. I don't see any conceptual roadblock
to the notion that we living control systems can do what that
simulation does.
Right. The problem is to find the _right_ logic, and by using the Test
with the real organism, to demonstrate that it accounts for behavior
under all the possible conditions.
P.S. Got the program for your meeting. Having PCT represented at a non-
PCT meeting by two people, you and Dennios Delprato, will be a first for
us!
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Best to all,
Bill P.