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[Steve Lehar]

In  his  final communication Jim  Bower  strikes at   the heart of his
differences  with  biological  connectionist philosophy.   While  many
connectionists believe that their paradigm bears both a structural and
functional   similarity  to   brain and  mind, and  is  thus a   valid
theoretical tool for   exploring those entities, Bower  believes  that
connectionism is  no     closer to   understanding   the  brain   than
conventional  AI  or  any     other   paradigm.    My      "180-degree
misunderstanding"  of his  former posting was (I am  left to guess) in
thinking  that he  opposed ALL theoretical modeling,   whereas what he
opposes is all theoretical modeling of the BRAIN.

It seems that Bower  is ferverently convinced  that the  mechanisms of
the   brain  are a deep dark  secret  that will   not  yield to simple
investigations with numerical models.

This is a curious view in an age  when science has successfully probed
the  atomic  element   of the brain,    the neuron, sufficiently    to
understand its major mode of operation.  Models at  this level he does
not  oppose,  so   long  as  they    restrict themselves  to  strictly
reproducing the experimental data.  But  when the theoretical insights
gained from such models  are   generalized to information   processing
models, that, says Bower is going too far.

I agree with Bower that many of today's popular neural models are very
remote from  actual biology, and there exists  a need to close the gap
between the abstract  mathematical type models like  backprop, and the
lower level models like the Hartline and Ratliff model.  In fact, that
is the major thrust of the work of people like Grossberg.  What I find
very curious  is Bower's   resistance to this  kind of  effort.  Bower
says...

 "It  is  true that  there is a   growing effort to  apply connectionist
  modeling techniques  to actual brain  structures.  This network is not
  the right place to  discuss this still relatively  minor  component of
  connectionism."

I cannot disagree more!  This network is exactly the  place to discuss
such  models, since these  are the  kind of models that give direction
and validity to the more abstract models.  If these  models are only a
minor  component of  connectionism,  that is a  regretable fact  which
needs   to be  corrected by  more discussion of   these models.  Bower
continues...

 "However, I will say that  I fail to  be convinced of the usefulness of
  these models, and furthermore, I am  concerned that these  efforts may
  actually  serve to  further  obscure  the  distinctions  between brain
  organization and the  organization of connectionist models."

Of course they will obscure the distinction between brain organization
and connectionist models.  That is exactly the purpose of such models,
to show  the  commonality between  the  brain and the   models.  Bower
firmly believes that this commonality does not exist, and therefore it
is fruitless to try to find it...

 "As  a neurobiologist,  however, I would  assert that  even a cursory
  look at the brain reveals  a  structure having very little in common
  with  connectionist    models.  it is a    question    of  the basic
  computational   assumptions underlying network    construction (node
  structure,  feed  forward  components,  information  encoding, error
  detecting, learning, overall complexity)."

A cursory glance at  the brain reveals  multitudes of simple computing
elements richly interconnected with synaptic  links.  You say that has
LITTLE to do with connectionist models?  That was the very INSPIRATION
for connectionist models!  Now if  we have  some of the details wrong-
node structure, feedback etc.,  then let us CORRECT those deficiencies
in order to more closely model the brain.  In  fact, those are exactly
the kinds of  issues addressed by   the  more biological connectionist
models like  Grossberg's,  which   have dynamic   properties  and rich
feedback connections precisely for that reason.  Bower objects...

 "if these things are changed substantially,  then I would say  one no
  longer has a connectionist model."

It doesn't matter what they're CALLED, you can call them whatever you
like.  What's important is that emulate the functional architecture of
the brain.

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(O)((O))(((               slehar at park.bu.edu               )))((O))(O)
(O)((O))(((    Steve Lehar Boston University Boston MA     )))((O))(O)
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