On 3/30/2015 10:17 PM, Bruce Kellett wrote:
meekerdb wrote:
On 3/28/2015 11:36 PM, Bruce Kellett wrote:
Bruno has acknowledged that this is not what the MGA shows. MGA simply shows that his
version of computationalism is incompatible with physical supervenience. This cannot
be seen as surprising since it is explicitly built into computationalism that
physicalism is false.
That's not my understanding. Bruno's argument starts with assuming that a part, or
all, of your brain could be replaced by a digital AI with the same I/O and if done at a
suitably low level of detail (probably neuronal) you conscious inner life would be
essentially the same. That seems to me to be assuming physicalism as the basis of
consciousness.
This contradicts what you say below about Bruno assuming that only certain special
processes institute consciousness.
He's trying a reductio. So he assumes physicalism - that some physical processes produce
consciousness (not just any physical process) - and tried to reach the absurdity that the
physical process can be a do-nothing process.
I think there is an ambiguity, or uncertainty, about just what the program that is to
replace part or all of your brain does. If the program is just a simulation of the
actual physical brain, neuron by neuron, synapse by synapse, so that that physical laws
that govern the behaviour of these brain elements are instantiated by the computer, and
act on the initial data given by the state of the brain when the program is started,
then there will be no essential difference between the program and the brain it
replaces. In this case you might say "Yes, doctor", with some confidence. The necessary
programming would presumably be well understood since the brain is deterministic at the
level with which we are concerned, and the physical/chemical laws can be determined. If
the initial state can be ascertained with sufficient precision without killing you, then
the simulated computer brain substitute acts just like the original, so should give no
problems.
This understanding is based on the idea that consciousness supervenes on the processes
and states of the physical brain. These have been replaced by equivalent physical
processes, so consciousness should remain intact. There is no appeal to computationalism
here.
Sure there is; it's the requirement that the computer compute the equivalent physical
processes. They are equivalent in the sense of producing the same sequence of states (at
whatever level they are simulated).
The simulating computer has to perform many detailed calculations to carry through the
operation of known physical laws on the initial data, but I don't think anyone is saying
that consciousness supervenes on such calculations.
I think they are. In fact didn't you say so above: "...then the simulated computer brain
substitute acts just like the original, so should give no problems." Are you making some
distinction between simulating the brain and simulating the physics of the brain?
The other approach is to assume that the computer used to replace your brain is running
a true AI program. It is not simulating the physical processes piece by piece, but
running some black box program that has been shown to reproduce known brain outputs for
some range of suitable inputs. The program is presumably supposed to implement the
universal TM computations upon which consciousness supervenes independently of the
underlying hardware/wetware. If this is the model you have in mind, then the
computationalist model directly contradicts physical supervenience, right from the outset.
No, as I understand it Bruno is assuming the doctor replaces all or part of your brain
with a digital device (or even an analog one so long as it's function doesn't depend on
infinite precision) that computes the same I/O function at it's interface with the rest of
you.
Now, I think the interesting question to ask is: "Given these two different
implementations of the brain replacing program, would you have equal confidence in both
possibilities?"
I think the answer would, in general, be "No!". The program that assumes physical
supervenience can be tested element by element, so that once it has been shown to truly
follow the known chemical and physical laws, and accurately reproduces the structure of
your actual brain, it will be counterfactually correct, and could be trusted into the
future.
The alternative, computationalist model cannot be tested in this way. Basically because
it is necessarily holistic. Consciousness is assumed to supervene on a particular type
of computation, but is your computationalist program the same as mine? How do we know? I
do not think the we could ever guarantee that such an AI device was counterfactually
correct for /your/ brain. Many artificial learning programs, based on neural nets or the
like, can be trained to perform with great reproducibility on the training data set, but
fail miserably once one goes outside this data set. They are not counterfactually
correct, and I do not know how you could ever ensure the necessary counterfactual
correctness, even if you did imagine that you knew precisely the sort of computation
upon which consciousness supervened.
So I would reject the computationalist program right at the start -- I would not say
"Yes, doctor" to that sort of AI program.
Nor would I or Bruno. But what about the other kind of simulation. It is still reducible
to a program running on a UTM - except for interaction with the world outside the brain.
As I understand it Bruno finesses this problem by (1) saying the subject is conscious
while dreaming so the external world isn't necessary to consciousness or (2) if it's
necessary whatever part of it that is necessary can be added to the UTM simulation.
Once you have consciousness instantiated by a UTM program then he and Maudlin argue that
the computation can be inert.
I think that's his argument, but Bruno can correct me if I'm wrong.
Brent
Bruce
The MGA is, therefore, largely irrelevant, because it does not prove anything that we
didn't already know. It certainly does not show that consciousness is an abstract
process in Plationia, independent of any physical process.
Bruno assumes that only some special processes instantiate consciousness and these are
characterized by being computations of some kind, i.e. a sequence of states that could
be realized by a program running on a Universal Turing Machine (not necessarily
halting). Since the consciousness computation defined this way is an abstract
mathematical process in Platonia; it is equivalent to assuming consciousness is
instantiated by an abstract mathematical process.
Brent
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