harnad@mind.UUCP (Stevan Harnad) (10/27/86)
On mod.ai, in Message-ID: <8610160605.AA09268@ucbvax.Berkeley.EDU> on 16 Oct 86 06:05:38 GMT, eyal@wisdom.BITNET (Eyal mozes) writes: > I don't see your point at all about "categorical > perception". You say that "differences between reds and differences > between yellows look much smaller than equal-sized differences that > cross the red/yellow boundary". But if they look much smaller, this > means they're NOT "equal-sized"; the differences in wave-length may be > the same, but the differences in COLOR are much smaller. There seems to be a problem here, and I'm afraid it might be the mind/body problem. I'm not completely sure what you mean. If all you mean is that sometimes equal-sized differences in inputs can be made unequal by internal differences in how they are encoded, embodied or represented -- i.e., that internal physical differences of some sort may mediate the perceived inequalities -- then I of course agree. There are indeed innate color-detecting structures. Moreover, it is the hypothesis of the paper under discussion that such internal categorical representations can also arise as a consequence of learning. If what you mean, however, is that there exist qualitative differences among equal-sized input differences with no internal physical counterpart, and that these are in fact mediated by the intrinsic nature of phenomenological COLOR -- that discontinuous qualitative inequalities can occur when everything physical involved, external and internal, is continuous and equal -- then I am afraid I cannot follow you. My own position on color quality -- i.e., "what it's like" to experience red, etc. -- is that it is best ignored, methodologically. Psychophysical modeling is better off restricting itself to what we CAN hope to handle, namely, relative and absolute judgments: What differences can we tell apart in pairwise comparison (relative discrimination) and what stimuli or objects can we label or identify (absolute discrimination)? We have our hands full modeling this. Further concerns about trying to capture the qualitative nature of perception, over and above its performance consequences [the Total Turing Test] are, I believe, futile. This position can be dubbed "methodological epiphenomenalism." It amounts to saying that the best empirical theory of mind that we can hope to come up with will always be JUST AS TRUE of devices that actual have qualitative experiences (i.e., are conscious) as of devices that behave EXACTLY AS IF they had qualitative experiences (i.e., turing-indistinguishably), but do not (if such insentient look-alikes are possible). The position is argued in detail in the papers under discussion. > Your whole theory is based on the assumption that perceptual qualities > are something physical in the outside world (e.g., that colors ARE > wave-lengths). But this is wrong. Perceptual qualities represent the > form in which we perceive external objects, and they're determined both > by external physical conditions and by the physical structure of our > sensory apparatus; thus, colors are determined both by wave-lengths and > by the physical structure of our visual system. So there's no apriori > reason to expect that equal-sized differences in wave-length will lead > to equal-sized differences in color, or to assume that deviations from > this rule must be caused by internal representations of categories. And > this seems to completely cut the grounds from under your theory. Again, there is nothing for me to disagree with if you're saying that perceived discontinuities are mediated by either external or internal physical discontinuities. In modeling the induction and representation of categories, I am modeling the physical sources of such discontinuities. But there's still an ambiguity in what you seem to be saying, and I don't think I'm mistaken if I think I detect a note of dualism in it. It all hinges on what you mean by "outside world." If you only mean what's physically outside the device in question, then of course perceptual qualities cannot be equated with that. It's internal physical differences that matter. But that doesn't seem to be all you mean by "outside world." You seem to mean that the whole of the physical world is somehow "outside" conscious perception. What else can you mean by the statement that "perceptual qualities represent the form [?] in which we perceive external objects" or that "there's no...reason to expect that...[perceptual] deviations from [physical equality]...must be caused by internal representations of categories." Perhaps I have misunderstood, but either this is just a reminder that there are internal physical differences one must take into account too in modeling the induction and representation of categories (but then they are indeed taken into account in the papers under discussion, and I can't imagine why you would think they would "completely cut the ground from under" my theory) or else you are saying something metaphysical with which I cannot agree. One last possibility may have to do with what you mean by "representation." I use the word eclectically, especially because the papers are arguing for a hybrid representation, with the symbolic component grounded in the nonsymbolic. So I can even agree with you that I doubt that mere symbolic differences are likely to be the sole cause of psychophysical discontinuities, although, being physically embodied, they are in principle sufficient. I hypothesize, though, that nonsymbolic differences are also involved in psychophysical discontinuities. > My second criticism is that, even if "categorical perception" really > provided a base for a theory of categorization, it would be very > limited; it would apply only to categories of perceptual qualities. I > can't see how you'd apply your approach to a category such as "table", > let alone "justice". How abstract categories can be grounded "bottom-up" in concrete psychophysical categories is the central theme of the papers under discussion. Your remarks were based only on the summaries and abstracts of those papers. By now I hope the preprints have reached you, as you requested, and that your question has been satisfactorily answered. To summarize "grounding" briefly: According to the model, (learned) concrete psychophysical categories are formed from sampling positive and negative instances of a category and then encoding the invariant information that will reliably identify further instances. This might be how one learned the concrete categories "horse" and "striped" for example. The (concrete) category "zebra" could then be learned without need for direct perceptual ACQUAINTANCE with the positive and negative instances by simply being told that a zebra is a striped horse. That is, the category can be learned by symbolic DESCRIPTION by merely recombining the labels of the already-grounded perceptual categories. All categorization involves some abstraction and generalization (even "horse," and certainly "striped" did), so abstract categories such as "goodness," "truth" and "justice" could be learned and represented by recursion on already grounded categories, their labels and their underlying representations. (I have no idea why you think I'd have a problem with "table.") > Actually, there already exists a theory of categorization that is along > similar lines to your approach, but integrated with a detailed theory > of perception and not subject to the two criticisms above; that is the > Objectivist theory of concepts. It was presented by Ayn Rand... and by > David Kelley... Thanks for the reference, but I'd be amazed to see an implementable, testable model of categorization performance issue from that source... Stevan Harnad {allegra, bellcore, seismo, packard} !princeton!mind!harnad harnad%mind@princeton.csnet (609)-921-7771