Brent meeker writes:
> > Let's not try to define consciousness at all, but agree that we know what it is
> > from personal experience. Computationalism is the theory that consciousness arises
> > as a result of computer activity: that our brains are just complex computers, and
> > in the manner of computers, could be emulated by another computer, so that
> > computer would experience consciousness in the same way we do. (This theory may be
> > completely wrong, and perhaps consciousness is due to a substance secreted by a
> > special group of neurons or some other such non-computational process, but let's
> > leave that possibility aside for now). What we mean by one computer emulating
> > another is that there is an isomorphism between the activity of two physical
> > computers, so that there is a mapping function definable from the states of
> > computer A to the states of computer B. If this mapping function is fully
> > specified we can use it practically, for example to run Windows on an x86
> > processor emulated on a Power PC processor running Mac OS. If you look at the
> > Power PC processor and the x86 processor running side by side it would be
> > extremely difficult to see them doing the "same" computation, but according to the
> > mapping function inherent in the emulation program, they are, and they still would
> > be a thousand years from now even if the human race is extinct.
> >
> > In a similar fashion, there is an isomorphism between a computer and any other
> > physical system, even if the mapping function is unknown and extremely
> > complicated.
>
> I don't see how there can be an isomorphism between any two systems. Without some
> structural constraint that seems to throw away the "iso" part and simply leave a
> morphism.
The definition of the structural constraint is part of the isomorphism. Some isomorphisms are
more economical than others, but there are no God-given isomorphisms or structural constraints.
The limiting case is simply a lookup table mapping any arbitrary system to another arbitrary
system. That this is inelegant does not make it invalid.
> >That's not very interesting for non-conscious computations, because
> > they are only useful or meaningful if they can be observed or interact with their
> > environment. However, a conscious computation is interesting all on its own. It
> > might have a fuller life if it can interact with other minds, but its meaning is
> > not contingent on other minds the way a non-conscious computation's is.
>
> Empirically, all of the meaning seems to be referred to things outside the
> computation. So if the conscious computation thinks of the word "chair" it doesn't
> provide any meaning unless there is a chair - outside the computation. So it is not
> clear to me that meaning can be supplied "from the inside" in this way. I think this
> is where Bruno talks about "the required level of substitution" and allows that the
> level may be the brain at a neural level PLUS all the outside world. So that within
> this simulation the simulated brain is conscious *relative* to the rest of the
> simulated world.
I don't think it is right to say that the brain is *conscious* relative to the environment. It is
intelligent relative to the environment, whether that means able to communicate with another
conscious being or otherwise interacting with the environment in a meaningful way. Although
we deduce that a being is conscious from its behaviour, and you can only have behaviour
relative to an environment, only the being itself directly experiences its consciousness. This is
the 3rd person/ 1st person distinction.
> >I know
> > this because I am conscious, however difficult it may be to actually define that
> > term.
>
> But do you know you would be conscious if you could not interact with the world?
> That seems doubtful to me. Of course you can close your eyes, stop your ears, etc
> and still experience consciousness - for a while - but perhaps not indefinitely and
> maybe not even very long.
Maybe there is something about my brain that would render me unconscious if all outside
input stopped, but that seems to me a contingent fact about brains, like the fact that I
would be rendered unconscious if my oxygen supply were cut off. A hallucination is defined
as a perception without a stimulus and there are millions of people in the world who have
hallucinations all the time. Sometimes people are so overwhelmed by hallucinatory experiences
that you could saw their leg off and they don't notice, which is in part how dissociative
anaesthetics like ketamine work. If you like, you can say that consciousness is maintained by
one part of the brain interacting with another part of the brain: one part is program, the other
part data, or one part is computer, the other part environment. The point is, whatever you
choose to call it, an isolated physical system can experience consciousness.
> > The conclusion I therefore draw from computationalism is that every possible
> > conscious computation is implemented necessarily if any physical process exists.
>
> That would seem to require mappings that are not isomorphisms.
How do you define the non-isomorphic mappings?
> > This seems to me very close to saying that every conscious computation is
> > implemented necessarily in Platonia, as the physical reality seems hardly
> > relevant.
>
> It seems to me to be very close to a reductio ad absurdum.
Like Bruno, I am not claiming that this is definitely the case, just that it is the case if
computationalism is true. Several philosophers (eg. Searle) have used the self-evident
absurdity of the idea as an argument demonstrating that computationalism is false -
that there is something non-computational about brains and consciousness. I have not
yet heard an argument that rejects this idea and saves computationalism. Personally,
I would bet in favour of computationalism being true, but I cannot say that I am sure.
Stathis Papaioannou
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Received on Thu Sep 07 2006 - 22:41:39 PDT