Bruno Marchal wrote:
On 26 Mar 2015, at 08:05, Bruce Kellett wrote:
I simply say, so what! Counterfactual equivalence does not have any
independent justification, and it is highly unlike to be sensible,
even in the context of computationalism.
You are quick here.
I might explain the stroboscope machinery which might help me to ask you
what you mean by consciousness supervening to a recording, given that no
computation at all is involved in the recording.
Basically, because the simulation of any given conscious state can be
carried out an any computer -- whatever the architecture, physical
construction, or programming language. As long as the original state
is accurately simulated, the conscious state will be the same.
It is not the state which must be correctly simulated, it is the
relation between those state/ You need the truth of the proposition IF
the input change, I do some this or that". That truth is part of what
define my person, and it is not applied in the movie. The movie is a
sequence of description of states, not a sequence of states related by
some universal number.
As is usual with debates of this kind, I think we are talking about two
different things. When you introduce the possibility of the Dr replacing
your brain with a simulation, you mean "an artificial intelligence
program initialized by the synaptic weights read out from your old
brain". In other words, this is not simply a recording of the state of
the brain at one instant, it is a full description that would enable the
brain to be reconstructed. In other words, it is a prescription for
producing a model of your brain -- a simulation.
I agree it is clear that this model is conscious only when it is
running. If you write down the Godel number of the description, that is
a static object and would not be considered conscious in itself. But
this description could be used to build a model in any medium, be it a
computer, or a system composed of billiard balls. Provided the exact
details are modelled, the model will be conscious when the simulation is
run.
The other thing (that seems to be introduced with the MGA) is the we
observe the active brain and record it from instant to instant in
sufficient detail that we can observe which neurones are active, which
connections are made, and in which order. This is effectively the
"movie". It records a certain period of conscious activity, but it does
not contain the information necessary to construct a model that can go
on operating independently outside the original recording period.
The question is: if I replay the recording of the second type, do I
recreate the conscious experience? Note that this is not a simulation in
the normal sense, it is a replay of a recording of the relevant parts of
the brain undergoing conscious activity. If conscious supervenes on the
physical brain so that the pattern of connections and neurone firings
constitute the physical manifestation of the conscious experience, then
rerunning the recording will recreate the conscious experience.
It is essentially the same as if I am running the simulation on the
computer I observe all the registers and memory of this computer then
recreate exactly this pattern of registers and memory data by some other
means than by running the original program. If one creates a conscious
experience, then so does the other.
The argument seems to be that the replay of the recording will not
recreate the conscious experience because it is not counterfactually
correct. I do not think that it has been demonstrated that this is
relevant. If exactly the same physical activity of the brain has been
replayed, then exactly the same consciousness would be experienced. This
is the meaning, as I see it, of saying that consciousness supervenes on
the physical state of the brain (or, probably more correctly, on the
sequence of physical states). Sure, replaying the movie does not
reconstruct an individual that can go on functioning independently once
the movie finishes -- but that was not the idea. We are reproducing a
conscious moment, not simulating a conscious entity in its entirety.
The Movie Graph Argument is an attempt to argue that this concept of
physical supervenience is absurd, so that consciousness supervenes only
on the (counterfactually correct) computation. I think the argument
fails because it assumes what it attempts to prove. Namely, it assumes
that physical supervenience is false (absurd).
Bruce
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