What the Neocortex Does

John H. johnhkm at netsprintXXXX.net.au
Thu Aug 3 19:00:24 EST 2000


Kevin K. <KK at _._> wrote in message news:3989A9BB.D2BC1B29 at _._...
>
>
> Harry Erwin wrote:
> >
> > Kevin K. <KK at _._> wrote:
> >
> > > Harry Erwin wrote:
> > >
> > > > On the other hand, it has some
> > > > relevance to Church's thesis, since I haven't been able to identify
the
> > > > mechanism of a Turing machine (or any of the alternatives) in the
> > > > anatomy 8).
> > >
> > > You're not going to find a Turing machine in the nervous system of a
> > > bat. A Turing machine is an infinite object. Any biological system of
> > > nerves with binary states is a finite automata, and thus can be
> > > simulated by a Turing machine. Therefore, you will never find
something
> > > a bat can do which a TM cannot do, and Church's thesis is unaffected.
> > >
> > > Kevin K.
> >
> > Ah, but neurons do not have binary states.
>
> I was under the impression that they do, i.e. firing or not firing.
>
> > In fact, to define the state
> > of a neuron, you have to treat it as a continuous extended object.
>
> That doesn't prove anything. The same can be said about the logic gates
> on chip. Such gates are in a condition of continuous flux due to thermal
> fluctuations, noise, varying distributions of electrons etc. But these
> variations have no effect on the behavior of the chip as a computational
device.

The variations do affect neurons though, very much so. And not just via
glial cells either, the whole environment is doing things to affect signal
transmission; sometimes in very surprising ways (eg rapid NO diffusion).


> > It
> > gets worse when you're dealing with a collection of neurons, because you
> > now need to keep track not only of the internal states of the neurons
> > but also the glial cells. So we're not dealing with a finite automaton.
>
> So you are saying that, in principle, the function of a bat brain cannot
> be simulated by a digital computer, no matter how advanced? I find that
> very extravagant.

I don't know if its extravagant, but I fail to see your confidence that a
computer can truly simulate brain function. I'm not even sure that neurones
transmit information or bits or whatever, I'm more enclined to some
'ensemble' of neurones creating the symbols or representations. I don't
know, and I can't find enough support to suggest that brains are just
computational devices; there appears to be something else again. I can't
separate memory from cognition, but AI seems to operate on the assumption
that in brains these are separate functions.

I remain confused, but this is an interesting thread.


John H.
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