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.
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 These have been replaced
by equivalent physical processes, so consciousness should remain intact.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. 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.
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.
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.
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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