Re: Neural netss (was Re: death of the mind.)

From: dan michaels (feedbackdroids_at_yahoo.com)
Date: 09/01/04 

Date: 1 Sep 2004 12:14:18 -0700

dralexgreen@yahoo.co.uk (Alex Green) wrote in message news:<42c8441.0408310302.18e48308@posting.google.com>...

> >
> > The phrase may in fact mislead, since it implies a comparison (and the
> > comparison has been explicitly invoked by some contributors to this
> > thread.) But I don't see any comparison happening - there is AFAIK no
> > "comparator module" that takes input from the "perception module" and
> > the "face recognition module" and outputs "Yup, that's Johnny."
>
> In the cerebellum the output signals for motor control are comparator
> outputs.
>
> Wherever we see feedback in a biological system we should suspect a
> comparison is occurring. The way the entire percept in the cortex
> switches in binocular rivalry would be expected from the feedback from
> cortex to LGN.
>

Exactly so, I think, regards feedback [esp negative variety]. The
exact location of the effect TBD. There are so many cortical areas
that contribute.

Regards positive FB, this is conceivably good for complementing,
boosting, and sustaining on-going activity, whereas negative FB is
good for making comparisons, and also regulating on-going activity.
This is the way to prevent pos-FB effects from overrunning their
bounds, both in local and in more global regions of neural tissue.
Look at the many many studies, by Eccles and others, where nerves
coming into cortical regions were stimulated and cells recorded
intracellularly. The typical response is a quick activation followed
by a sustained inhibition. Neg-FB is used in general for regulation of
activity. Stellate cells are activated to produce recurrent
inhibition, etc.
===============

> >
> > The reason I keep talking about brain physiology as I understand it is
> > that I've never been happy with abstract models that ignore the messy
> > details. "Reference state" is such a concept, since it applies to
> > devices that function differently than NNs.
>
> Interacting NN's such as modules in the cortex or cortex and LGN could
> easily create the required operations.
>

Indeed.
================

>
> I suspect that current simulated NN's do not have adequate or
> appropriate functions to enrich the analysis of the data. Although the
> brain is a topographic processor it also contains analysis modules,
> some as small as sets of interneurones. The incoming data stream is
> enriched with analyses of many different types, also arranged
> topographically and also capable of involvement in the neural net.
>

The present systems are not complex enough. By analogy, it took the
brain going from 1-2B neurons in dogs/cats and 10B in monkies/chimps
all the way to 100B in humans before the really cool stuff emerged.
==================

> However, this still leaves us with another problem. How can our
> experience be our own neurone activity, the activity that is based on
> the percept? This can only be answered by introducing scientific
> theories that go beyond information processing.
>
> Best Wishes
>
> Alex Green

Nicholas Humphrey made a nice comment about this ....

"... for human beings, to 'feel a sensation' is to be author,
audience, and enjoyer of the reverberant activity, rolled into one
..."

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