harnad@mind.UUCP (Stevan Harnad) (06/05/87)
John Cugini <Cugini@icst-ecf.arpa> asks: > (1) I wonder why the grounding is to depend on invertibility rather than > causation and/or resemblance? > > (2) Isn't it true that physically distinct > kinds of light (eg. #1 red-wavelength and green-wavelength vs. > #2 yellow-wavelength) can cause completely indistinguishable > sensations (ie subjective yellow)? Is this not, then, a non-invertible, > but nonetheless grounded sensation? (1) According to my view, invertibility (and perhaps inversion) captures just the relevant features of causation and resemblance that are needed to ground symbols. The relation is between the proximal projection (of a distal object) onto the sensory surfaces -- let's call it P -- and an invertible transformation of that projection [I(P)]. The latter is what I call the "iconic representation." Note that the invertibility is with the sensory projection, *not* the distal object. I don't believe in distal magic. My grounding scheme begins at the sensory surfaces ("skin and in"). No "wider" metaphysical causality is involved, just narrow, local causality. Of course the story is more complicated, because iconic representations are not sufficient to ground a symbol referring to an object. They're not even enough to allow a device to reliably pick out the object and give it the right name (i.e., to categorize or identify it). "Categorical representations" are needed next, but these are no longer invertible into the sensory projection. They are feature-filters preserving only the (proximal) properties of the object's sensory projection that reliably distinguish the object (let's say it's an "X") from the other objects that it can be confused with (i.e., relevant "non-X's" in the particular context of confusable alternatives sampled to date). Then finally the labels ("X," "non-X") can be used as the primitive symbols in a (now *grounded*) symbol system, to be combined and otherwise syntactically manipulated into meaningful composite symbol-strings (descriptions). (2) Your question about indistinguishable but distinct colors mistakes my grounding scheme for a "wide" metaphysical grounding scheme -- one where the critical "causality" would be in the relation between distal objects and our internal representations of them, whereas mine is a narrow, skin-and-in grounding proposal. I have dubbed this view "approximationism," and, without going into details (for which you may want to consult the CP book or a reprint of the theoretical chapter), the essence of the idea is that internal representations are always approximate rather than "exact," in two important senses. The iconic representation is approximate up to its grain of resolution (the "jnd" or "just-noticeable-difference"): Think of it as a Principle of the "Iconic Identity of Iconic Indiscernibles": What you can't tell apart is the same to you. The categorical representations are approximate in an even more important sense: The only features the category filter picks out are the ones that are needed in order to identify the confusable alternatives in the context you have sampled to date. Hence an X is just what your current, approximate, provisional context-dependent feature-filter picks out reliably from among the X's and Non-X's you have encountered so far: "The Categorical Identity of Unsorted or Unsortable Members" (i.e., X's are identically X's unless and until reliably identified or identifiable otherwise). Since this is not a "wide" grounding, there is nothing oracular or omniscient or metaphysical about what the X is that this picks out. There is no God's-eye view from which you can say what X's "really" are. There's just the mundane historical fact -- available to an outside observer, if there is one -- about what the actual distal objects were whose proximal projections you were sampling. Those furnished your context, and your fallible, context-dependent representations will always be approximate relative to those objects. In conclusion, the only differences in the object that are reflected in the iconic and categorical representations are the ones present in the proximal projection of the alternatives sampled to date (and preserved by the category-feature filter). The representations are approximate (i.e., indifferent) with respect to any further distal differences. Symbolic discourse may serve to further tighten the approximation, but even that cannot be "exact," if for no other reason than that there's always a tomorrow, in which the context may be widened and the current representation may have to be revised. -- But that's another story, and no longer concerns the grounding problem but what's called "inductive risk." -- Stevan Harnad (609) - 921 7771 {bellcore, psuvax1, seismo, rutgers, packard} !princeton!mind!harnad harnad%mind@princeton.csnet harnad@mind.Princeton.EDU