Requests

[Steve Hanson]

"Biological plausibility" is somewhat of a throwaway, given
the massively documented understanding we have of
learning in brain circuits (he said sarcastically).   
There are many seemingly incompatible brain circuits for
implementing classical conditioning,
depending on the beast, the stimuli, and the context and maybe
just depending on the whims of the local circuitry development
that day.

Certainly, the way Backprop is typically implemented in "C" code,
may be biologically implausible... ie information doesn't
tend to flow back down axons... (at least not at 
a fast enough rate).   I am not sure that slow rate
of convergence is such a good argument.. given you
can do things to speed up learning in feedforward nets... also given
the rate people really seem to learn at...

In any case, there are now published counter-examples of
people showing how back-prop could be seen as biologically
plausible, which I suspect given our present state knowledge
is a much more useful enterprise.

to wit:

G. Tesauro,  Neural Models of Classical Conditioning: A theoretical
Perspective,  Hanson & Olson, (Eds.)  MIT Press, Bradford, 1990.

D. Zipser,  in  Gluck & Rumelhart, Neuroscience and Connectionism,
LEA, 1990.

There may be others....

	--Steve





Stephen J. Hanson
Learning & Knowledge Acquisition Group 
SIEMENS Research 
755 College Rd. East
Princeton, NJ 08540