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From: kovsky@netcom.com (Bob Kovsky)
Subject: Re: how does it work in brain?
Message-ID: <kovskyD9tD0v.2sD@netcom.com>
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Date: Wed, 7 Jun 1995 17:38:55 GMT
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Brian Dixon <briand@cv.hp.com> quoted me and wrote:
>Bob Kovsky (kovsky@netcom.com) wrote:
>
>
>: 	Of course, some neural networkers will say that the architecture 
>: of the neural network mimics that of the brain.  Indeed, that's why the 
>: name "neural network" was chosen.  T'ain't so. Artificial neural networks 
>: ignore half of brain function:  the chemical environment which modifies 
>: the electrical activity and which is, apparently, modified in turn.  
>
>You missed the point.  The adjustment of weights and bias' in an ANN is
>*designed to mimic neuronal elasticity*.  Study the text From Neuron to
>Brain by Nichols, Martin, and Wallace.  The rest of the "electrical
>activity", the connectionist views and transmission issues, are indeed
>modeled by ANNs.  The primary difference between how ANNs and NNs such as
>the brain is *how* learning takes place, that is, how neuronal elasticity is
>accomplished.  In ANNs, weights and bias' are modified by an artificially
>created algorithm, sic back propagation.  In NNs, elasticity is accomplished
>by changes in synaptic efficacy, which in turn is changed by means of 
>changing availabilities of neurotransmitters in the presynaptic cell.

Reply:  Chemical <environment> means more than synaptic efficiency.  It 
means that groups of real-life neurons are subject to group influences.   
Neuroscientists who study the chemistry of the brain consider the organ 
to be akin to a gland.   Moreover, modifications of the chemical 
environments occur over a wide range of time spans, from the millisecond 
speed at the synaptic level to the diurnal rate of the circadian 
(day-night) cycle.

In other words, to translate to engineering parlance, there are a 
multitude of feedback modes, not the single mode of ANN's.

[abstaining from further response]


-- 

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    Bob Kovsky          |  A Natural Science of Freedom 
    kovsky@netcom.com   |  Materials available by anonymous ftp
                        |  At ftp.netcom.com/pub/fr/freedom
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