[From Bill Powers (940224.1730 MST)]
Martin Taylor (930424.1140) --
In the standard hierarchy, there is a "category" level. I
observed that categories can apply to almost any analogue
perception where the world seems usually to have a logical
exclusion, such as that a blue object is not at the same time a
red object. Using this observation, I proposed that the
category level, which is already an interface level between
analogue and symbolic control levels, should be conceived as
being connected simultaneously to all lower levels, rather than
just to the event (?) level. This places the symbolic levels
beside rather than above the analogue levels.
The fact that a signal indicating "blue" is not the same as a
signal indicating "red" doesn't have anything to do with
categories (necessarily). Different perceptions are carried on
different pathways; they are in different places. "Not blue" does
not mean "red," and vice versa. Nor is there anything to prevent
a particular color from appearing both blue and red (to different
systems): for example, purple will excite both blue-detectors and
red-detectors at the sensation level. Some of the names we give
to colors are there strictly to handle cases that lie between
whatever we have learned to call "pure" colors (which is hardly
standardized).
In your definition of a category level, it seems to me that you
are focusing on an almost-irrelevant side-issue (mutual
exclusivity) and failing to answer the main question, which is
_what kind of operation generates a category perception_?
I proposed that the *kind* of perception involved in the
category level was analogous to the operation of a flip-flop,
in that the perception of one of a set of mutually exclusive
categories actively inhibited the possible perception of any of
the others.
This proposal assumes that we already have two systems which
respond to inputs by generating signals that have a categorical
meaning. This skirts the primary question: what kind of operation
will provide a signal when one or more members of a category is
present? Whether or not the signals are made mutually exclusive,
we must state how perception of either an apple or a grape can
lead to the category-perception "fruit." This is quite
independent of whether we go further to propose that "fruit" and
"vegetable" are to be mutually exclusive, a result that could be
achieved by a positive-feedback cross-connection between the two
category-recognizers, or simply by a logical convention. In
principle, this mutual exclusivity could be established between
any two categories: "house" and "automobile," for example -- and
furthermore, people could argue as to whether an object could be
both at the same time (a motor home).
When we get into the realm of logical argument about whether two
categories are or are not, or should or should not be, mutually
exclusive, then we are no longer talking about basic capacities
of the brain. We are just using brains to manufacture arguments:
pushing words around in a logical framework.
The essence of the category level is that a number of disparate
input signals, meaning quite different lower-level perceptions,
come to evoke _one single signal_. A wallet, a house, a computer,
a car, all evoke in me a sense that they are "mine", and that any
one of them or any combination of them is "mine." This has
nothing to do with objects that are not mine -- the essential
problem is to say what kind of perceptual operation would create
this relationship between lower-level perceptions and a category-
level perception. The simplest kind of operation I can think of
is the "OR". A category signal is produced by or-ing together all
the signals representing the individual members of the category.
Nothing else seems required.
Mutual exclusivity can be added at the logic level; it is not
needed, and indeed is not called for, at the category level. Two
categories can be mutually exclusive in one context yet can
coexist in another. If I say that no daughter of mine will have a
child out of wedlock, I am saying that a person can't
simultaneously be my daughter and an unmarried mother, so if my
daughter turns up pregnant I must either force her to have an
abortion or disown her to keep the exclusive-or true. Yet in
another context, I would have to admit that this person is in
fact both an unmarried mother and my daughter (this is not an
autobiographical example). The mutual exclusivity depends on my
logic, not on the categories "unmarried mother" and "daughter."
All this indicates to me that mutual exclusivity is not a
property of the category level, but of the way the logic level
chooses to deal with category signals. I am shown a purple
object, and am asked "Is it blue?" I answer "Yes, somewhat." If I
am asked "Is it red?" I also answer "Yes, somewhat." Only if I
feel that objects must _logically_ either be one color or the
other must I choose one word -- and then I would have to say that
since it is not exclusively blue or exclusively red, it is
neither, and it must be purple and only purple. But that is not a
categorical consideration; it is a logical consideration. And one
person's logic is not necessarily another's.
At the stage in which our model-building exists now, I see no
merit in trying to add complexities to it. Rather, we should be
trying to boil it down to the simplest form possible that still
covers the main phenomena. We need to define levels that are
simple enough to test. Treating every proposal in the basic model
as a springboard for leaping to other possibilities, especially
irrelevant ones, does not further our progress.
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Best,
Bill P.