On 3/7/2010 9:46 PM, Jack Mallah wrote:
--- 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 incidental.
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).

I agree with this view, but perhaps for a different or additional reason. I think consciousness can only be consciousness *of* something; it requires a context that gives the information processing of thought a semantics through interaction with a world. This world needs to have regularities (causal laws) in order for the interaction to produce semantics.

--- 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 
remaining brain.

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.

I think it is likely that there are some metabolic processes that maintain quantum coherence for show periods of time, as photosynthesis seems to. But I don't see any place for that in brain information processing as opposed to metabolism.

Brent Meeker

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, 
I think.

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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