Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!amdahl!nsc!andrew From: andrew@nsc.nsc.com (andrew) Newsgroups: comp.ai.neural-nets Subject: Re: NN Question Summary: system clocks may even be detrimental Message-ID: <10192@nsc.nsc.com> Date: 15 Mar 89 20:24:46 GMT References: <32125@gt-cmmsr.GATECH.EDU> <8903071701.AA12290@shire.cs.psu.edu> <11114@pasteur.Berkeley.EDU> Organization: National Semiconductor, Santa Clara Lines: 56 In article <11114@pasteur.Berkeley.EDU>, brp@sim.uucp (bruce raoul parnas) writes: > neurons each evolve on their own, independent of system clocks. > > >Two burning questions which, in my mind, are among the > >most important open questions in neural networks research are: > >1. Is unclocked behaviour important? Was the non-availability > > of a system clock something that Nature had to fight to overcome, > > or did it bring inherent advantages? > > i believe that a system clock would be more of a hindrance that a help. > studies with central pattern generators and pacemaker activity (re: the heart) > show clearly that system clocks are not unavailable. if evolution had found > a neural system clock advantageous, one could have been created. i feel, > however, that the continuous-time evolution of neural systems imbues them > with their remarkable properties. > Having just browsed through "Fractals Everywhere" by Barnsley, I'm reminded of a comment about the heart and clocks in there. Loosely paraphrased, it is stated that a healthy heart exhibits a measurable degree of chaotic behaviour - i.e. the fractal dimension of some representation of the heartbeat over time - whereas a low or zero fractal dimension (a very steady beat) is an excellent indicator that something unhealthy - an attack or arhythmia - is imminent. This may say something in general about organic systems as you've been discussing; that exact synchronisation is not something desirable. Further, I believe Walter Friedman has presented recently on information processing _in vivo_ where he postulates that chaotic attractors are a key element in biological information processing. I'm afraid that's as much detail as I have - I'm not "into chaos". Therefore, although, as you say, locality of processing tends to exclude a system clock approach, the above give perhaps stronger reasons as to why a manmade ANNS would actually be inferior, were it to use a system clock. While I'm here, I'll mention something else from biology, which filled me with great dismay(!) - this month's Scientific American's feature on the brain's star-like "astrocyte" cells. Their role becomes important in direct proportion to the amount of time they are investigated; akin to glial cells, I believe. Now the diagram of how the astrocytes connect to the neuron net is frightening .. they hook between everywhere (neuron body, node of Ranvier on the axon myelin sheath tap point, on the bare axon, capillaries, and the cells at both the surface (meningeal) and the centre (water-bearing) cells of the whole brain. This means computationally that it's a whole new ball game, I imagine... anyone have any comments? ========================================================================== DOMAIN: andrew@logic.sc.nsc.com ARPA: nsc!logic!andrew@sun.com USENET: ...{amdahl,decwrl,hplabs,pyramid,sun}!nsc!logic!andrew Andrew Palfreyman, MS D3969 PHONE: 408-721-4788 work National Semiconductor 408-247-0145 home 2900 Semiconductor Dr. there's many a slip P.O. Box 58090 'twixt cup and lip Santa Clara, CA 95052-8090 ==========================================================================