Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!gatech!hao!husc6!diamond.bbn.com!aweinste From: aweinste@Diamond.BBN.COM (Anders Weinstein) Newsgroups: comp.ai,comp.cog-eng Subject: Re: The symbol grounding problem Message-ID: <6358@diamond.BBN.COM> Date: Fri, 5-Jun-87 13:12:10 EDT Article-I.D.: diamond.6358 Posted: Fri Jun 5 13:12:10 1987 Date-Received: Tue, 9-Jun-87 07:14:26 EDT References: <764@mind.UUCP> <768@mind.UUCP> <770@mind.UUCP> <6174@diamond.BBN.COM> <6211@diamond.BBN.COM> <792@mind.UUCP> Reply-To: aweinste@Diamond.BBN.COM (Anders Weinstein) Organization: BBN Laboratories, Inc., Cambridge, MA Lines: 99 Keywords: icons, categories, symbols, grounding Xref: mnetor comp.ai:488 comp.cog-eng:109 In reply to my objection that >> invertibility has essentially *nothing* to do with the difference >> between analog and digital representation according to anybody's >> intuitive use of the terms Stevan Harnad (harnad@mind.UUCP) writes in message <792@mind.UUCP>: >There are two stages of A/D even in the technical sense. ... Unless the >original signal is already discrete, the quantization phase involves a >loss of information. Some regions of input variation will not be retrievable >from the quantized image. The transformation ... cannot be inverted so as to >recover the entire original signal. Well, what I think is interesting is not preserving the signal itself but rather the *information* that the signal carries. In this sense, an analog signal conveys only a finite amount of information and it can in fact be converted to digital form and back to analog *without* any loss. But in any case the point I've been emphasizing remains: the A/A transformations you envisage are not going to be perfect (no "skyhooks" now, remember?), so preservation or loss of information alone won't distinguish an (intuitively) A/A from an A/D transfomation. I think the following reply to this point only muddies the waters: > I agree that there may be information loss in >A/A transformations (e.g., smoothing, blurring or loss of some >dimensions of variation), but then the image is simply *not analog in >the properties that have been lost*! It is only an analog of what it >preserves, not what it fails to preserve. You can take this line if you like, but notice that the same is true of a *digitized* image -- in your terms, it is "analog" in the information it preserves and not in the information lost. This seems to me to be a very unhappy choice of terminology! Both analog and digitizing transformations must preserve *some* information. If all you're *really* interested in is the quality of being (naturally) information-preserving (i.e. physically invertible), than I'd strongly recommend you just use one of these terms and drop the misleading use of "analog", "iconic", and "digital". > The "symbol grounding problem" that has >been under discussion here concerns the fact that symbol systems >depend for their "meanings" on only one of two possibilities: One is >an interpretation supplied by human users... and the other is a physical, >causal connection with the objects to which the symbols refer. >The surprising consequence is that a "dedicated system" -- one that is >hard-wired to its transducers and effectors... may be significantly different >from the very *same* system as an isolated symbol-manipulating module, >cut off from its peripherals ... With regard to this "symbol grounding problem": I think it's been well-understood for some time that causal interaction with the world is a necessary requirement for artificial intelligence. Recall that in his BBS reply to Searle, Dennett dismissed Searle's initial target -- the "bedridden" form of the Turing test -- as a strawman for precisely this reason. (Searle believes his argument goes through for causally embedded AI programs as well, but that's another topic.) The philosophical rationale for this requirement is the fact that some causal "grounding" is needed in order to determine a semantic interpretation. A classic example is due to Georges Rey: it's possible that a program for playing chess could, when compiled, be *identical* to one used to plot strategy in the Six Day War. If you look only at the formal symbol manipulations, you can't distinguish between the two interpretations; it's only by virtue of the causal relations between the symbols and the world that the symbols could have one meaning rather than another. But although everyone agrees that *some* kind of causal grounding is necessary for intentionality, it's notoriously difficult to explain exactly what sort it must be. And although the information-preserving transformations you discuss may play some role here, I really don't see how this challenges the premises of symbolic AI in the way you seem to think it does. In particular you say that: >The potential relevance of the physical invertibility criterion >would only be to cognitive modeling, especially in the constraint that >a grounded symbol system must be *nonmodular* -- i.e., it must be hybrid >symbolic/nonsymbolic. But why must the arrangement you envision must be "nonmodular" ? A system may contain analog and digital subsystems and still be modular if the subsytems interact solely via well-defined inputs and outputs. More importantly -- and this is the real motivation for my terminological objections -- it isn't clear why *any* (intuitively) analog processing need take place at all. I presume the stance of symbolic AI is that sensory input affects the system via an isolable module which converts incoming stimuli into symbolic representations. Imagine a vision sub-system that converts incoming light into digital form at the first stage, as it strikes a grid of photo-receptor surfaces, and is entirely digital from there on in. Such a system is still "grounded" in information-preserving representations in the sense you require. In short, I don't see any *philosophical* reason why symbol-grounding requires analog processing or a non-modular structure. Anders Weinstein BBN Labs