From: hal@finney.org
Date: Fri Jun 18 1999 - 19:56:28 MDT
One of the articles in the collection The Mind's I, edited by Hofstadter
and Dennett, has always struck me as posing difficult problems relating
to instantiation and playback questions. It is The Story of a Brain, by
Arnold Zuboff. I will summarize a portion here. This is a simplification
of Zuboff's arguments but I think catches the main idea.
A man greatly admired by his society has died. However in order to show
their gratitude and love, his people have taken it upon themselves to
preserve his brain and induce pleasant experiences in it. They believe
that by stimulating his neurons in appropriate patterns they are able
to create the corresponding conscious experiences.
At first this is just done by stimulating the sensory inputs to the brain,
but over time the brain is separated into parts and the various inputs to
each part are stimulated separately. Since everyone in the society wants
to participate in this act of devotion, eventually it gets to where each
person is responsible for just one neuron of the original brain.
The neurons sit in small neutrient baths, and when it is time for a new
experience to be delivered, each person receives instructions for the
timing of how they are to stimulate their neuron. At the appropriate
moment, each person delivers the specified patterns of stimulation all
over the world, and the neurons go through the same patterns of activity
which they would have if they were actually in the man's brain when he
was experiencing some pleasurable activity. It is still thought that
by doing this they actually bring about the corresponding mental state.
Now it happens one day that just when a new experience-delivery is about
to begin, one person finds that his neuron has died. He knows that this
won't affect the overall experience, since neurons die all the time and
we can't tell if there are a few more or less. But he is personally
disappointed because he knows that he will not be able to play his own
small part in delivering the happy experience.
Then he gets an idea. His own brain is full of neurons as well, firing
all the time. At the appropriate time, he moves the neural bath out of
the way and bends over and puts his own brain into the position where
"his" neuron is normally kept. Since his own brain is active, he is
sure to have a neuron fire which is in the right place and at the right
time for each of the stimulations he is supposed to give. In this way
he can participate in delivering the experience using the neurons in
his head rather than the one in the bath.
But then he thinks, why bend over? It doesn't matter where the neurons
are located, all that matters is the pattern of their stimulation.
And then he thinks, what about all the other people who are stimulating
their own neurons? They have brains too, full of neurons just like his.
Any time they were supposed to be stimulating their neuron in its bath,
they had neurons in their head which were firing at exactly that moment.
If all that is necessary to produce a conscious experience is to have
neurons fire at the specified times and places, there is no need for
anyone to stimulate anything. Just by standing there, their own brains
provide more than enough neural firings to produce any neural pattern
(and therefore any mental experience) imaginable.
It would seem to follow, then, that the entire enterprise has been
a folly. Either all possible mental states are existing all the time
just due to random neural firings in disconnected brains all over the
world, or else these carefully planned stimulations, which were designed
to mimic actual neural patterns in a conscious brain, were not actually
producing any mental states.
So, what do you think? Were they producing mental states by stimulating
those neurons? And if so, are they still produced when they just stand
their and let their brains do the work of firing neurons?
Hal
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