Gödel, Escher, Bach An Eternal Golden Braid by Douglas R. Hofstadter

AI program

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software levels
\ J

electronic

substrate

I

' "symbol" level' ~ ___ ....,I macroscopic ')

of brain (mind). I world

\ J seml- \

isomorphism J

(representation

I brain ,

( (intermediate J

\ levels) J

neural

substrate

of knowledge)

microscopic

world

"ultimate

substrate"

(laws of physics)

FIGURE 108. Crucial to the endeavor of Artificial Intelligence research is the notion that

the symbolic levels of the mind can be "skimmed off" of their neural substrate and implemented

in other media, such as the electronic substrate of computers. To what depth the copying of

brain must go is at present completely unclear.

Is an ability to play checkers well a sufficient indicator of intelligence?

If so, then AI already exists, since checker-playing programs are of world

class. Or is intelligence an ability to integrate functions symbolically, as in a

freshman calculus class? If so, then AI already exists, since symbolic inte-

gration routines outdo the best people in most cases. Or is intelligence the

ability to play chess well? If so, then AI is well on its way, since chess-playing

programs can defeat most good amateurs; and the level of artificial chess

will probably continue to improve slowly.

Historically, people have been naive about what qualities, if

mechanized, would undeniably constitute intelligence. Sometimes it seems

as though each new step towards AI, rather than producing something

which everyone agrees is real intelligence, merely reveals what real intelli-

gence is not. If intelligence involves learning, creativity, emotional re-

sponses, a sense of beauty, a sense of self, then there is a long road ahead,

and it may be that these will only be realized when we have totally dupli-

cated a living brain.

Beauty, the Crab, and the Soul

Now what, if anything, does all this have to say about the Crab's virtuoso

performance in front of Achilles? There are two issues clouded together

here. They are:

Church, Turing, Tarski, and Others 573