|
|
More on Churchland
John McCreery (JLM@TWICS.COM)
Tue, 19 Sep 1995 23:26:56 +0900
In my last message, I was talking about Patricia Churchland's
_Neurophilosophy_ and had just noted that her animus is
directed against the idea that the "software" studied by
philosophers and cognitive psychologists can be isolated from the
"hardware" of neurophysiology. I then found myself late for
work and ended the message too abruptly to be clear about what
I was saying. Here I resume that thread.
Speaking historically, Churchland notes that the the basic division
of software and hardware reflects a categorical split as old as
Western philosophy. It starts, perhaps, with Plato's dividing the
world of Ideas from the world of Matter and returns full force to
the modern world in Descartes' division between Mind and Body.
It also reflects, of course, the Christian conception of the soul
which survives the mortal body and will be reborn in a new
body at the Resurrection.
If, however, Churchland were merely rehearsing familiar
materialist arguments she would not be as interesting as she is.
She observes that the software imagined by cognitive
psychologists and philosophers characteristically takes the form
of sentential logic, i.e., a logic in which sentences are related
sequentially by formal rules that govern valid sequences. The
mind is thus conceived as operating like a program written to
run on a single CPU that can process only one instruction at a
time. The central difficulty of programs written in this way
which attempt to mimic the operations of human thinking is
combinatorial blowup. They require literally millions and billions
of steps to calculate the contingencies involved in apparently
simple acts, e.g., recognizing a familiar face. (More complex
calculations would require more steps than the number of
electrons in the visible universe!) But, as Churchland observes,
and Helmholtz demonstrated, nerve impulses travel much slower
than the speed of sound. If, while silicon switches operate at
nanosecond speeds, neurons fire in milliseconds, so that even the
simplest reflexes require between 100 and 200 milliseconds,
how, then, can the brain outperform the computer? The answer
must be some form of massively parallel processing with
cascading operations whose form is not at all that of sequential,
sentential logic. The alternative may, for example, be something
like matrix operations on tensors which--and here is where it
gets interesting--do a good job of modeling prototype effects,
where inputs can depart in varying degrees from a prototypical
image. Voila! We are suddenly talking formal systems that give
us a handle on things like "family resemblances" a la
Wittgenstein, "polythetic classifications," "metaphors," etc. We
may be looking at the first radically new empirical view of how
the mind operates since Aristotle wrote the _Organon_ (a view
supported on other grounds by anthropologically minded
linguists like George Lakoff in _Women, Fire and Dangerous
Things_). Of course, all this is speculative. But it's nicely grounded
speculation and a powerful stimulus to fresh thought.
Why should a humanist with only the shakey remnants of college
level math worry about such things? As Churchland observes, we
may be on the verge of new ideas that shatter the folk
psychologies with which we usually operate. Where will that
leave us?
John McCreery
Yokohama
Tuesday, September 19, 1995
|