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Meaning derives from embodiment and function, understanding arises when concepts are meaningful in this sense and truth is considered to arise when the understanding of a statement fits one's understanding of a situation closely enough for one's own purposes. Thus, there is no absolute truth or God's-eye view. Our view of what exists (metaphysics) is not independent of how we know it (epistemology). [G. Edelman 1992][p. 250]
We now return to the subject of Chapter ,
discussing some of these issues in the light of the model of color
perception and color naming we have presented.
I consider the model of color perception and color naming as presented in
this dissertation to be a true referential semantic model in the domain of
(basic) color names. It is true in the sense that it is well-defined and
computable, and enables certain behaviors that require a semantic model to
bridge the gap between the external world and internal symbols, and
referential in the sense that it expresses the meaning of color terms in
terms of a mapping to/from another domain. The referents of the color terms
are not directly objects or properties in the world, however, but certain
areas in an internally represented color space. But the color space itself
is causally connected to the outside world, which I consider a necessary
property for any referential semantic model, or at least for the models
that constitute the ``direct grounding'' for some set of terms. Other terms
may derive their meaning from being systematically related to directly
grounded ones, but without such a core set of directly grounded terms, I
believe no meaning or understanding is possible. To put it succinctly: no
amount of semantics will ever allow a robot to relate its internal symbols
to its environment without some set of directly grounded terms. The
algorithm for determining compound color names as presented in
Section may be regarded as a primitive compositional
semantic characterization of such terms, which are indirectly grounded in
the meanings of (characteristic functions of) the set of basic color
terms. I therefore do not agree with an extreme solipsistic view of
semantics that would hold that the world is permanently ``out of reach'' of
cognition, and that it therefore does not matter how we choose to
characterize the meanings of concepts, as long as this characterization is
internally consistent. Meaning is a function of at least two variables:
what is ``out there'', and what is ``in here''. The world and the cognitive
mechanisms both have a necessary role in meaning and understanding. An
agent equipped with an arm can actually reach out and touch the things out
there that in its internal representation correspond to the referents of
some of its internal symbols, and while one may contend that the referent
of its symbols is really part of its internal representation and not part
of the external world, the difference is not relevant for most practical
purposes. One might consider the internal thing to be the ``direct
referent'' and the external thing the ``indirect referent'', and in most
cases they will be causally related.
It is possible, however, to uncouple this ``alignment'' (see
Appendix
) under certain circumstances, and in this
case we might speak of ``being deceived by one's senses'' (as in optical
illusions) or of ``perceptual defects'' (as in blindness).
A ubiquitous red herring in writings about semantics is truth. Truth, of
the metaphysical God's-eye variety, has very little to do with meaning, in
my opinion. The Edelman quote above expresses this sentiment quite
well. The often-found Tarskian statement that ``snow is white if and only
if snow
is
white
'', where
x
denotes the referent of x (an object or relation over
objects) is of no use if those referents are assumed to be in the world,
and one is supposed to verify the metaphysical, God's-eye truthfulness of
the description of the state of affairs, without the intervention of any
perceptual or cognitive mechanism. The most one can say is ``I believe snow
is white if and only if
'', where
is a point in
color space corresponding to a sample of an image of something belonging to
the perceptual class ``snow''. Usually, though not always, this will be
the case when one has the appropriate white and cold stuff in one's field
of view. It is futile to torture oneself with existential doubt as to
whether what one is beholding is ``really'' snow, or merely a very good
imitation of it. The duck test applies.
With our concrete model of basic color term semantics before us, it is also
easy to see what makes a symbolic representation symbolic. The labels
in equations
are the (names of the) symbols we use for the
perceptual categories that they are paired (associated) with. They carry
meaning only by virtue of being associated with those categories, but there
is nothing intrinsic about them that makes them mean what they mean. The
association is arbitrary, and can easily be changed without changing
anything fundamental about our understanding of color. A rose would look
just as red by any other color name, so to speak. What is not
arbitrary is the perceptual model, however, since changing any parameters
in there will literally make us see the world differently. The perceptual
categories might thus be considered analog or iconic in nature, as opposed
to symbolic. This also sheds some light on how translation is possible.
Without any perceptual underpinnings, the knowledge that ``red'' = ``rood''
does not mean much at all. While it may allow us to syntactically
substitute one for the other, it would not help us much if we were to move
to Flanders. But in the presence of the perceptual category, knowing that
``red'' = ``rood'' allows us to move to Flanders and understand what people
mean when they talk about ``rood'' things, and pick out the referents in
the world without any further learning. I contend that without a more or
less common set of perceptual categories (and hence directly grounded
terms), learning a foreign language would not be possible - indeed it
would not be possible to understand what anyone else is talking about, and
probably it would not be possible to learn any language at all.
Some related issues are brought up in [Davidoff \& Concar 1993], where the authors discuss the ``memory palette'' for colors, or the ``internal color space'' which functions as a link between the mental worlds of color vision and color language. They report that children have difficulty learning color names: red, green, yellow, and blue are learned first, in no particular order, and only when all four of these are learned can they use any of them correctly. These colors have been called ``landmark colors''. They are easy to name, form associations with, and children prefer to point to examples of them. They play a central role in learning to name other regions of the color space. Categorization is reported to be not necessarily hardwired, and to some extent alterable by experience. It can be impaired while color vision itself is intact. These findings support the two-stage model of a color space with a separate set of categorization functions defined on that space, and the ``looseness'' of the coupling between perceptual color categories and color names. Some similar views can be found in [G. Edelman 1989], who mentions research in pre-verbal concepts and complains that concepts and their names are usually tied together in computational models, which is not the case in our model of course. As will have become obvious by now, I share the view of cognition as being based in perception.
With respect to Knowledge Representation and Reasoning issues, the color
model can be seen as providing the direct grounding for a set of atomic
concepts (base nodes in SNePS terminology, cf. [Shapiro \& Rapaport 1987]).
These may in turn take part in reasoning about color or about colored
objects, but I believe that to be relevant, such reasoning must take the
semantics of these terms (the perceptual model) into account, for instance
in determining the meaning of compound color names based on the meanings of
their constituent terms, as was hinted at in Section .
In other words, meaningful reasoning requires meaningful terms. Such
meaning must derive directly or indirectly from grounding through
perception and action (see Appendix
), and cannot be
based on imaginary worlds or descriptive semantics in manuals.