Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ptsfa!ames!rutgers!princeton!mind!harnad From: harnad@mind.UUCP Newsgroups: comp.ai,comp.cog-eng Subject: Re: The symbol grounding problem Message-ID: <847@mind.UUCP> Date: Mon, 15-Jun-87 01:21:36 EDT Article-I.D.: mind.847 Posted: Mon Jun 15 01:21:36 1987 Date-Received: Tue, 16-Jun-87 01:24:03 EDT References: <764@mind.UUCP> <768@mind.UUCP> <770@mind.UUCP> <6174@diamond.BBN.COM> <8264@ut-sally.UUCP> Organization: Cognitive Science, Princeton University Lines: 77 Keywords: icons, categories, symbols, grounding, modularity, cognition Xref: utgpu comp.ai:489 comp.cog-eng:119 Summary: Internal analog retinas and model-theoretic semantics berleant@ut-sally.UUCP (Dan Berleant) of U. Texas CS Dept., Austin, Texas has posted this welcome reminder: > the retina cannot be viewed as a module, only loosely > coupled to the brain. The optic nerve, which does the coupling, has a > high bandwidth and thus carries much information simultaneously along > many fibers. In fact, the optic nerve carries a topographic > representation of the retina. To the degree that a topographic > representation is an iconic representation, the brain thus receives an > iconic representation of the visual field. > Furthermore, even central processing of visual information is > characterized by topographic representations. This suggests that iconic > representations are important to the later stages of perceptual > processing. Indeed, all of the sensory systems seem to rely on > topographic representations (particularly touch and hearing as well as > vision). As I mentioned in my last posting, at last count there were 12 pairs of successively higher analog retinas in the visual system. No one yet knows what function they perform, but they certainly suggest that it is premature to dismiss the importance of analog representations in at least one well optimized system... > Yes, the Turing test is by definition subjective, and also subject to > variable results from hour to hour even from the same judge. > But I think I disagree that intrinsic meaningfulness cannot be > objectively verified. What about the model theory of logic? In earlier postings I distinguished between two components of the Turing Test. One is the formal, objective one: Getting a system to generate all of our behavioral capacities. The second is the informal, intuitive (and hence subjective) one: Can a person tell such a device apart from a person? This version must be open-ended, and is no better or worse than -- in fact, I argue that is identical to -- the real-life turing-testing we do of one another in contending with the "other minds" problem. The subjective verification of intrinsic meaning, however, is not done by means of the informal turing test. It is done from the first-person point of view. Each of us knows that his symbols (his linguistic ones, at any rate) are grounded, and refer to objects, rather than being menaningless syntactic objects manipulated on the basis of their shapes. I am not a model theorist, so the following reply may be inadequate, but it seems to me that the semantic model for an uninterpreted formal system in formal model-theoretic semantics is always yet another formal object, only its symbols are of a different type from the symbols of the system that is being interpreted. That seems true of *formal* models. Of course, there are informal models, in which the intended interpretation of a formal system corresponds to conceptual or even physical objects. We can say that the intended interpretation of the primitive symbol tokens and the axioms of formal number theory are "numbers," by which we mean either our intuitive concept of numbers or whatever invariant physical property quantities of objects share. But such informal interpretations are not what formal model theory trades in. As far as I can tell, formal models are not intrinsically grounded, but depend on our concepts and our linking them to real objects. And of course the intrinsic grounding of our concepts and our references to objects is what we are attempting to capture in confronting the symbol grounding problem. I hope model theorists will correct me if I'm wrong. But even if the model-theoretic interpretation of some formal symbol systems can truly be regarded as the "objects" to which it refers, it is not clear that this can be generalized to natural language or to the "language of thought," which must, after all, have Total-Turing-Test scope, rather than the scope of the circumscribed artificial languages of logic and mathematics. Is there any indication that all that can be formalized model-theoretically? -- Stevan Harnad (609) - 921 7771 {bellcore, psuvax1, seismo, rutgers, packard} !princeton!mind!harnad harnad%mind@princeton.csnet harnad@mind.Princeton.EDU