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Article 2099 of comp.ai.philosophy:
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>From: weemba@libra.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: comp.ai.philosophy
Subject: Re: From neurons to computation: how?
Message-ID: <60144@netnews.upenn.edu>
Date: 13 Dec 91 17:09:53 GMT
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In-reply-to: sarima@tdatirv.UUCP (Stanley Friesen)

In article <310@tdatirv.UUCP>, sarima@tdatirv (Stanley Friesen) writes:
>So, until the neurologists find a problem with the model of mind as the
>emergent product of neural data processing, I will apply KISS and assume
>that this model is correct, or at least a useful aproximation.

>And I mean computable in the sense that physical computers as we build them
>today could compute the same data transform as any given neuron (including
>the temporal variability we calling learning).

>I conclude it because all that I know about the operation of neurons (and
>that is considerable, since I am by background a biologist) is fully
>consistant with the theory that it is only the signalling properties
>of a neuron that are relevant to thought.

Etc.

So how many neurobiologists believe this?  I made a quickie random scan
of the literature and turned up none.  Those that I saw that did mention
computation did not seem to have any commitment to the digital.

I mention just three neurobiologists' negative opinions here.

>From Ira B Black INFORMATION IN THE BRAIN: A MOLECULAR PERSPECTIVE, pp2-3:

	The evidence ... represent[s] a frontal assault on the
	functionalist position and the popular computer metaphor.
	Shorn of all detail, the software-hardware dichotomy is
	artificial. ... Software and hardware are one [and] the
	same in the nervous system. ... Extensive evidence
	indicates that the brain is not an immutable series
	of circuits of invariant elements; rather it is in
	constant structural and functional flux. The digital
	computer analogy is fatally misleading.

Rodolfo R Llinas sometimes mentions "computational states" and the
like.  His mentions are incredibly weak for your thesis in light of
your alleged massive evidence for your alleged digital brains that
you say you have.  From SCIENCE, v242, p1661:

	How do the oscillatory properties of central neurons
	relate to the information-carry properties of the
	brain as a whole? In principle, one may propose that
	intrinsic electroresponsiveness generates internal
	computational states ... Brain function is proposed
	to have two distinct components, ... a "closed" [one
	for] subjectivity and semantics, and an "open" com-
	ponent ... for sensory-motor transformations.....

Note that these are oscillations that Llinas is referring to.  Not
signalling properties.  [The quantized states of these oscillations
are what the Marshall-Froehlich theory refer to, btw.]  And what
does Llinas do with this?  He goes on to refer to differential
equation models for these oscillations.  Not cellular automata.
Not Turing machines.  Not discrete dynamics.  He is, in other
words, using "computation" in the sense that a thrown ball "com-
putes" the shape of a parabola.

And indeed, in his MINDWAVES article, Llinas denies that his use of
computation (in that article) refers to digital computers.

I've already cited Gerald M Edelman in NEURAL DARWINISM and THE
REMEMBERED PRESENT and his rejection of the computer model.

So your "considerable knowledge" doesn't impress me.  Your belief that
it's just a matter of overcoming "sheer overwhelming *complexity*", at
which point this alleged software of the mind will be revealed, is a
bad joke.

I'd say that neurobiology is much like physics in this matter.  In
general, most physicists operate with no particular opinion about
a physical Church-Turing thesis.  It's irrelevant to their work.
A few, like Feynman and Fredkin, have speculated on computer models
for physics, and it remains a nice little cottage industry within
the big picture.  But that's it.  A mentalist Chuch-Turing thesis
is just as irrelevant to neurobiology.  It's an alien thought from
the AI community, good for amusing philosophy, but not much else.
-- 
-Matthew P Wiener (weemba@libra.wistar.upenn.edu)


