Re: Neural Nets Vs. Symbol Systems

From: Stanford, Graham (gjs295@soton.ac.uk)
Date: Fri May 24 1996 - 19:30:50 BST


WHAT IS THE DIFFERENCE BETWEEN A NEURAL NET AND A SYMBOL SYSTEM?

Neural nets are one possibility for how we might explain the mind
through reverse engineering. Like the brain they have interconnected
units, between which they pass activity, and the strength of these
connections may vary. However they do not have axons, dendrites, action
potentials or graded potentials, unlike the brain. Also, they are not
well suited to reasoning and logical inference, language or
calculation, in which respect they are obviously also unlike the
brain.

Symbols are arbitrary, basically they have no direct similarity to the
object they depict, they represent it. A symbol system, examples of
which could be mathematical formulae, recipes or even sentences, can be
manipulated using algorithms. For instance one formula such as y =
91x-23 can easily be rearranged to be for x in terms of y. Likewise a
sentence can be re-worded up to a point without changing its message or
correctness.

The key difference is that nets cannot manipulate in this way because
outputs are contained within its units. It cannot be manipulated to
construct new orders or sentences, to do this it would have to learn
the complete set of rules, for instance those governing algebra.



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