--- On Tue, 3/2/10, David Nyman <david.ny...@gmail.com> wrote:
> computationalist theory of mind would amount to the claim that consciousness
> supervenes only on realisations capable of instantiating this complete range
> of underlying physical activity (i.e. factual + counterfactual) in virtue of
> relevant physical laws.
Right (assuming physicalism). Of course, implementing only part of the range
of a computation that leads to consciousness might lead to the same
consciousness, if it is the right part.
> In the case of a mechanism with the appropriate arrangements for
> counterfactuals - i.e. one that in principle at least could be "re-run" in
> such a way as to elicit the counterfactual activity - the question of whether
> the relevant "physical law" is causal, or merely inferred, would appear to be
Causality is needed to define implementation of a computation because otherwise
we only have correlations. Correlations could be coincidental or due to a
common cause (such as the running of a movie).
--- On Fri, 3/5/10, Stathis Papaioannou <stath...@gmail.com> wrote:
> If the inputs to the remaining brain tissue are the same as they would have
> been normally then effectively you have replaced the missing parts with a
> magical processor, and I would say that the thought experiment shows that the
> consciousness must be replicated in this magical processor.
No, that's wrong. Having the right inputs could be due to luck (which is
conceptually the cleanest way), or it could be due to pre-recording data from a
previous simulation. The only consciousness present is the partial one in the
> computationalism is only a subset of functionalism.
I used to think so but the terms don't quite mean what they sound like they
should. It's a common misconception that "functionalism" means
"computationalism" generalized to include analog and noncomputatble systems.
"Functionalism" as philosophers use it focuses on input and output. It holds
that any system which behaves the same in terms of i/o and which acts the same
in terms of memory effects has the same consciousness. There are different
ways to make this more precise, and I believe that computationalism is one way,
but it is not the only way. For example, some functionalists would claim that
a 'swampman' who spontaneously formed in a swamp due to random thermal motion
of atoms, but who is physically identical to a human and coincidentally speaks
perfect English, would not be conscious because he didn't have the right
inputs. I obviously reject that; 'swapman' would be a normal human.
"Computationalism" doesn't necessarily mean only digital computations, and it
can include super-Turing machines that perform infinite steps in finite time.
The main characteristic of computationalism is its identification of
consciousness with systems that causally solve initial-value math problems
given the right mapping from system to formal states.
--- On Fri, 3/5/10, Charles <charlesrobertgood...@gmail.com> wrote:
> The only fundamental difficulty I can see with this is if the brain actually
> uses quantum computation, as suggested by some evidence that photopsynthesis
> does (quoted by Bruno in another thread) - in which case it might be
> impossible, even in principle, to reproduce the activity of the rest of the
> brain (I'm not sure whether it would, but it seems a lot more likely).
It seems very unlikely that the brain uses QC for neural processes, which are
based on electrical and chemical signals which decohere rapidly. Also, I
wouldn't make too much of the hype about photosynthesis using it - that seems
an exaggeration; you can't make a general purpose quantum computer just by
having some waves interfere. Protein folding might use it in a sense but again
nothing that could be used for a real QC.
But, that aside, even a quantum computer could be made partial. I think that
due to the no-signalling condition, the partial QC's interaction with the other
part amounts to some combination of unitary operations which can be perfomed on
the partial QC, and entanglement-induced decoherence. You would still have to
have something entangled with the partial QC but it wouldn't have to perform
the computations associated with the missing parts if you perform the right
operations on the remaining parts and know when to entangle or recohere things,
In any case, a normal classical computer could simulate a QC - which should be
good enough for a computationalist - and you could make the simulation partial
in the normal way.
I should also note that if you _can't_ make a partial quantum brain, you
probably don't have to worry about the things my argument is designed to
attack, either, such as substituting _part_ of the brain with a movie (with no
change in the rest) and invoking the 'fading qualia' argument.
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