AI, NN, CNS (central nervous system)

[Jim Bower]

In response to Steve Hanson's comment on my comment.
 
 	I think that Steve's remarks largely miss my primary point which is
simply that an assumed relationship between biology and connectionism/neural 
networks should not be used as a distinguishing feature with
respect to AI.  There is simply no strong recent historical evidence for
this relationship and the field itself is evolving independently of any 
association with real biological networks.  While this may be unfortunate, it
is not necessarily bad, and it is certainly pretty predictable.  
 	The points Steve does raise are potentially interesting, although it is
not clear to me that they are of general interest to readers of this network 
for the reasons just stated.  Briefly, however, Steve seems to be
confusing what I would refer to as Computational Neuroscience, with
Cognitive Neuroscience.  The two are quite different in their intent.  The
Koch and Segev book, for example, with which I am quite familiar as codirector 
of the course on which the book is based and having written two of
its chapters, describes models intended to shed light on structure/function 
relationships within the nervous system.  This is Computational
Neuroscience.  Using modeling to explore more abstract mental or cognitive 
functions is Cognitive Neuroscience from which connectionism largely 
grew and to which it mostly relates.  Thus, while computational modeling 
can be applied at any level of interest, where it may or may not be
"productive and valid", the real question is productive and valid for what. 
  	If you are interested in cognitive neuroscience, by all means make
models.  Remember, however, there is no necessary relationship between
these models and the way the brain actually does things.  Further, the
largest limitation on this connection is liable to be our poor understanding
of cognitive behavior to begin with.  Thus, in the absence of any example
to the contrary, I reject the idea that there is necessarily a continuity 
between all levels of modeling no matter how abstract or detailed.  And this
obviously has nothing to do with my favorite cells or circuits which was a
silly and inappropriate remark to begin with.
 	Briefly, I would also like to comment on Steve's tautology regarding
the necessity of interactions between experimentalists and modelers.  As
I believe he knows, a commitment to this interaction is at the very base
of my own research effort. In fact, it is my view that this interaction
should be so tight that modelers are also experimentalists.  Further, in
order for data to really constrain models, the models should generate data
obtainable with experimental techniques.  Practically,  this is far easier
if they are structurally realistic.  This is one of the reasons I doubt the
usefulness of abstract models for understanding brain function.  In addition, 
most abstract models are intent on proving that somebodies idea is
at best plausible and at worst correct.  In my view, the real value of a
tight connection between models and experiment is the possibility that
brain structure itself will provide new ideas as to functional organization. 
 	It is also exceedingly ironic that Steve warns against assuming that
the details of the brain don't matter.  Of course, it is precisely my point
that the details matter a great deal.  In fact, this is the reason I assert
that connectionist modeling is not biologically relevant.  The structures
of the vast majority of these models bear virtually no resemblance to the
actual structure of the brain.  They might even prove to be no closer than
complicated switchboards or aqueducts. 
 	Finally, a general comment that relates to this debate as well as the
debate about AI versus connectionist approaches.  There is clearly a
strong tendency to deal with potential conflicts by simply declaring that
we are all part of one big happy family.  While this might sooth egos, relieve 
self doubt, and provide new funding opportunities, I think it is important 
to resist the temptation.  In the process of amalgamation important 
distinctions can be washed out.  
 
Jim Bower
jbower at smaug.cns.caltech.edu