cugini@ICST-ECF.ARPA (06/12/87)
S. Harnad replies: > 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. Well, OK, glad you clarified that - I think there are issues here about the difference between grounding symbols in causation emanating from distal objects vs. grounding them in proximal sensory surfaces - (optical illusions, hallucinations, etc.) but let's pass over that for now. It still doesn't seem clear why invertibility should be necessary for grounding (although it may be sufficient). Frinstance, suppose we humans, or a robot, had four kinds of color receptors lurking behind our retinas (retinae?), which responded to red, green, blue and yellow wavelengths. And further suppose that stimulating the yellow receptors alone produced the same iconic representation as stimulating the red and green ones - ie both were experienced as plain old yellow, nor could the experiencer in any way distinguish between the yellows caused by the two different stimulations. (A fortiori, the experiencer would certainly not have more than one categorical representation, nor symbol for such experiences.) In short, suppose that some information was lost on the way in from the sensory surface, so we had a many to one (hence non-invertible) mapping. Would you then want to say that the symbol "yellow" was not grounded for such a being? John Cugini <Cugini@icst-ecf.arpa> ------
cugini@ICST-ECF.ARPA (06/17/87)
I hate to nag but... In all the high-falutin' philosophical give-and-take (of which, I admit, I am actually quite fond) there's been no response to a much more *specific* objection/question I raised earlier: What if there were a few-to-one transformation between the skin-level sensors (remember Harnad proposes "skin-and-in" invertibility as being necessary for grounding) and the (somewhat more internal) iconic representation. My example was to suppose that #1: a combination of both red and green retinal receptors and #2 a yellow receptor BOTH generated the same iconic yellow. Clearly this iconic representation is non-invertible back out to the sensory surfaces, but intuitively it seems like it would be grounded nonetheless - how about it? John Cugini <Cugini@icst-ecf.arpa> ------