AI, NN, BC, CNS

[Jim Bower]

Ideologies:  several comments on several comments
 
 	At the risk of redundancy, let me say again, that blurring distinctions
between fields (ideologies) should be avoided and that, in my opinion,
there is much less of a relationship between neurobiology and the vast
majority of what is going on in AI, NN, and connectionism than one would
be led to believe from reading overview books, or even tuning in to the
connectionist network.  Beyond that, however, there is also an essential
difference between what could be called "biological connectionism" and
computational neurobiology as I would like to have it defined.  This involves 
the process by which the available computational tools are applied
to particular problems.  Hartline and Ratliff looked at the specific structure 
of the Limulus eye and developed an abstract version of that specific
circuit to explore the capabilities of the circuit.  They did not, as 
connectionists, go looking for a brain circuit to which they could apply their
modeling tools.  The brain came first, the tools second.  In this case the
fact that their 1957 model is largely indistinguishable from several modern 
connectionist models is interesting but irrelevant.  Hartline and
Ratliff were not the first connectionists (which I do not believe is what
Terry was trying to say, but in this field could be taken that way anyway). 
As biologists, Hartline and Ratliff invented something new and important
by paying attention to the detailed structure of the brain as biologists.
Certainly they did this by using existing mathematical tools, what choice
is there.  But their approach must fall under the category of computational
neurobiology as distinct from what Dave Rumelhart in his excellent summary 
calls the "connectionist approach" to neuroscience and everything
else.  Again, the critical difference is whether a model is being used to
explore possibilities, or to demonstrate a preexisting idea.  Even an idea
about the nature of the representation of information.  This is a critical
distinction.  Most models, prominently including those of Grossberg et al,
are in the later category.  It should be obvious why biologists object to
such models.
 	There are many other comments that I am tempted to make on the last
few days discourse.  But I will refrain in the interest of limiting debate
that is not related to Touring machines and other acceptable subjects.  I
would like to say, however, that the Hartline/ Ratliff model is an outstanding 
example of why KNOWING biological details and focusing directly
on biological problems does matter.  Of course, if one is of the opinion
that the mind is something different from the brain, or that human intelligence 
is something above and beyond animal intelligence, then there is
little point in paying attention to brain details anyway.  And the debate
from here becomes more theological than ideological. 

"And to all a goodnight"


Jim Bower
jbower at smaug.cns.caltech.edu