Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!princeton!mind!harnad From: harnad@mind.UUCP (Stevan Harnad) Newsgroups: comp.ai,comp.cog-eng Subject: The symbol grounding problem: "Fuzzy" categories? Message-ID: <936@mind.UUCP> Date: Mon, 29-Jun-87 19:34:58 EDT Article-I.D.: mind.936 Posted: Mon Jun 29 19:34:58 1987 Date-Received: Wed, 1-Jul-87 02:22:42 EDT References: <764@mind.UUCP> <768@mind.UUCP> <770@mind.UUCP> <6174@diamond.BBN.COM> <1194@houdi.UUCP> Organization: Cognitive Science, Princeton University Lines: 107 Summary: On the difference between being a bird and being birdlike Xref: mnetor comp.ai:588 comp.cog-eng:157 In comp.ai.digest: Laws@STRIPE.SRI.COM (Ken Laws) asks re. "Fuzzy Symbolism": > Is a mechanical rubber penguin a penguin?... dead...dismembered > genetically damaged or altered...? When does a penguin embryo become > a penguin?... I can't unambiguously define the class of penguins, so > how can I be 100% certain that every penguin is a bird?... and even > that could change if scientists someday discover incontrovertible > evidence that penguins are really fish. In short, every category is a > graded one except for those that we postulate to be exact as part of > their defining characteristics. I think you're raising the right questions, but favoring the wrong answers. My response to this argument for graded or "fuzzy" category was that our representations are provisional and approximate. They converge on the features that will reliably sort members from nonmembers on the basis of the sample of confusable alternatives encountered to date. Being always provisional and approximate, they are always susceptible to revision should the context of confusable alternatives be widened. But look at the (not so hidden) essentialism in Ken's query: "how can I be 100% certain that every penguin is a bird?". I never promised that! We're not talking about ontological essences here, about the way things "really are," from the God's Eye" or omniscient point of view! We're just talking about how organisms and other devices can sort and label APPEARANCES as accurately as they do, given the feedback and experiential sample they get. And this sorting and labeling is provisional, based on approximate representations that pick out features that reliably handle the confusable alternatives sampled to date. All science can do is tighten the approximation by widening the alternatives (experimentally) or strengthening the features (theoretically). But provisionally, we do alright, and it's NOT because we sort things as being what they are as a matter of degree. A penguin is 100% a bird (on current evidence) -- no more or less a bird than a sparrow. If tomorrow we find instances that make it better to sort and label them as fish, then tomorrow's approximation will be better than today's, but they'll then be 100% fish, and so on. Note that I'm not denying that there are graded categories; just that these aren't them. Examples of graded categories are: big, intelligent, beautiful, feminine, etc. > You are entitled to such an opinion, of course, but I do not > accept the position as proven... (Why opinion, by the way, rather than hypothesis, on the evidence and logical considerations available? Nor will this hypothesis be proven: just supported by further evidence and analysis, or else supplanted by a rival hypothesis that accounts for the evidence better; or the hypothesis and its supporting arguments may be shown to be incoherent or imparsimonious...) > ...We do, of course, sort and categorize objects when forced to do so. > At the point of observable behavior, then, some kind of noninvertible > or symbolic categorization has taken place. Such behavior, however, > is distinct from any of the internal representations that produce it. > I can carry fuzzy and even conflicting representations until -- and > often long after -- the behavior is initiated. Even at the instant of > commitment, my representations need be unambiguous only in the > implicit sense that one interpretation is momentarily stronger than > the other -- if, indeed, the choice is not made at random. I can't follow some of this. Categorization is the performance capacity under discussion here. ("Force" has nothing to do with it!). And however accurately and reliably people can actually categorize things, THAT'S how accurately our models must be able to do it under the same conditions. If there's successful all-or-none performance, the representational model must be able to generate it. How can the behavior be "distinct from" the representations that produce it? This is not to say that representations will always be coherent, or even that incoherent representations can't sometimes generate correct categorization (up to a point). But I hardly think that the basis of the bulk of our reliable all-or-none sorting and labeling will turn out to be just a matter of momentary relative strengths -- or even chance -- among graded representations. I think probabilistic mechanisms are more likely to be involved in feature-finding in the training phase (category learning) rather than in the steady state phase, when a (provisional) performance asymptote has been reached. > It may also be true that I do reduce some representations to a single > neural firing or to some other unambiguous event -- e.g., when storing > a memory. I find this unlikely as a general model. Coarse coding, > graded or frequency encodings, and widespread activation seem better > models of what's going on. Symbolic reasoning exists in pure form > only on the printed page; our mental manipulation even of abstract > symbols is carried out with fuzzy reasoning apparatus. Some of this sounds like implementational considerations rather than representational ones. The question was: Do all-or-none categories (such as "bird") have "defining" features that can be used to sort members from nonmembers at the level of accuracy (~100%) with which we sort? However they are coded, I claim that those features MUST exist in the inputs and must be detected and used by the categorizer. A penguin is not a bird as a matter of degree, and the features that reliably assign it to "bird" are not graded. Nor is "bird" a fuzzy category such as "birdlike." And, yes, symbolic representations are likely to be more apodictic (i.e., categorical) than nonsymbolic ones. -- Stevan Harnad (609) - 921 7771 {bellcore, psuvax1, seismo, rutgers, packard} !princeton!mind!harnad harnad%mind@princeton.csnet harnad@mind.Princeton.EDU