Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!isi.edu!smoliar From: smoliar@isi.edu (Stephen Smoliar) Newsgroups: comp.ai.philosophy Subject: Re: Just Minds and Machines this time Message-ID: <16510@venera.isi.edu> Date: 26 Jan 91 23:51:33 GMT References: <11656.9101241836@s4.sys.uea.ac.uk> <1991Jan25.022026.12999@watdragon.waterloo.edu> Reply-To: smoliar@venera.isi.edu (Stephen Smoliar) Organization: Information Sciences Institute, Univ. of So. California Lines: 64 In article <1991Jan25.022026.12999@watdragon.waterloo.edu> cpshelley@violet.uwaterloo.ca (cameron shelley) writes: > In reviewing some short papers on >some new neural net work, I was struck by the notion of 'error' being >employed. One of the praises always sung of NN's is that they are >"robust", ie. no matter what input you give them, they won't simply >fail like symbolic programs, but will rather try to compensate and >produce a meaningful output. In other words (IMHO), all errors are >treated as noise and an attempt is made to ignore them. There is >essentially no notion of 'ill-formed' input as opposed to 'ill-transmitted' >input. I argued (in the review) that this is epistemologically >inadequate, at least as a model of human cognition, since humans >show the ability to do recovery from both types of error (in different >fashion). I want to pick up on this and perhaps try to assimilate it with Stuart Hampshire's recent article on Wittgenstein (actually his review of the new Monk biography) in THE NEW YORK REVIEW. Hampshire offers what I feel is an excellent summary of the essence of the TRACTATUS: According to the TRACTATUS the multiplicity of elements in a sentence ought to be a picture of the multiplicity of elements in a state of affairs. The formal correspondence secures for us the reference to a particular point in reality. To some extent, the idea that it makes sense to talk about such "a particular point in reality" at all was one of the major positions Wittgenstein chose to contest in his later work; but I find it interesting that much of connectionism almost seems to have translated this idea of "a particular point in reality" into a point in some multidimensional energy landscape. What counts as robustness is nothing more than the observation that these landscapes tend to be sufficiently smooth that perturbation of a starting point will not severely disrupt its trajectory along this landscape. Cam's observation that this is but one way of viewing what "error" might be is well taken; and perhaps it obliges us to go back and think some more about appropriate metaphors for these points in "reality." Let us suppose that we still have some sort of multidimensional space as a metaphor for reality; but rather than filling it with an energy landscape, suppose we instead insert a linkage structure, sort of like a linear undirected graph, as a model of an agent's "knowledge" (whatever that may mean). The reason I wish to appear to this metaphor is as an alternative to modeling reasoning in terms of the trajectory of a point in the space which seeks out an energy sink. Think, instead, of accommodating a point in space by asking how that linkage structure might get flexed, or, perhaps expanded, in such a way that it ultimately "meets" that point; that resulting "meeting" might then be regarded as an "interpretation" of that point. Given sufficiently liberal laws of what you could do with the linkages, any given point would obviously be subject to multiple interpretations, which would mean it is not really a fixed "point in reality" (which, as I assumed above, was one of the problems Wittgenstein was trying to get away from). From Cam's point of view, the question of whether or not the point is "well-formed" ultimately boils down to whether or not the linkages can be configured to "meet" it. I realize this is all rather loose metaphor. (I also remember what John McCarthy recently had to say about metaphors.) However, since the purpose of this bulletin board is to kick around philosophical approaches, I regard this as yet another pebble to toss in the pond. Anyone who wishes to make waves is certainly welcome to do so. -- USPS: Stephen Smoliar 5000 Centinela Avenue #129 Los Angeles, California 90066 Internet: smoliar@venera.isi.edu