X-Message-Number: 8594 From: Thomas Donaldson <> Subject: Re: CryoNet #8546 - #8551 Date: Sun, 14 Sep 1997 16:18:27 -0700 (PDT) Hi again! I note that John Clark is aware of neural nets. While it's probably possible to make a Turing machine which would implement the workings of billions of neurons together, it seems unlikely that it could do so in any time we (or even we if we attain the immortality we are seeking) would consider reasonable. Recognition is not a task performable by a PRACTICAL Turing machine. Our nervous system (for some of this you must be a reader of PERIASTRON, sorry!) also has a feature which MIGHT be impossible for a Turing machine to emulate. The best current ideas about how memory forms (in brains, guys, in brains) involve growth of new connections between neurons. This comes from actual observations. It may also involve growth of new neurons, including in adults (readers of PERIASTRON will know why I say this). Question (I'm not fooling, but then I'd want to give this more thought before I answered, so I really mean it as a question): the classical Turing machine is given a tape, which it moves along marking individual digital spaces. If we allow formation of new connections and even new neurons, this tape becomes endless not only at both ends but even in the middle. (A system which does this might also signal the addition of new tape with some code at its front and back, just so the Turing machine doesn't get confused). This system allows addition of new tape upon new tape upon new tape, it's not a single-time thing. Among other effects would be that what was once a simple code written by the Turing machine would become quite complex over time, with the overlays). I am certainly aware of all the ideas for mapping, say, a digital N-dim infinite set of points to a single 1-dim sequence of points. Perhaps that solves the problem of equivalence and perhaps not: remember that such a mapping would have to change constantly as the Turing machine proceeded. For PRACTICAL purposes the case is good that neural nets, especially ones sprouting new connections and new neurons, can't be imitated by a Turing machine. Perhaps Mr. Pietrzak will save me the trouble of looking up the proofs in books by giving an opinion here. Long long life, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=8594