Stathis Papaioannou wrote:
Yes, I can see that. By aggregating the brain into one computation do
you mean replacing it with a synchronous digital computer whose program
would not only reproduce the I/O of individual neurons, but also the
instantaneous state on signals which were traveling between them (since
presumably timing is important to the neurons function)? Or do you mean
replacing it with a synchronous digital computer which produces the same
I/O at the afferent and efferent nerves? In the former case, it seems
that "thoughts" would be distributed over many, not necessarily
sequential, computational steps. In the later it would not be possible
to map the the computational steps to brain states at all since they are
only required to be the same at the I/O; and hence difficult to say what
constituted a thought.
Given these to two possible models of functionalism, I'm not clear on
what "the same computation" means. Are these two doing the same
computation because they have the same I/O? Over what range of I does
the O have to be the same - all possible? all actually experienced?
those experienced in the last 2minutes?
2010/1/13 Brent Meeker <meeke...@dslextreme.com>:
You're asserting that neuron I/O replication is the "appropriate level" to
make "brain behavior" the same; and I tend to agree that would be sufficient
(though perhaps not necessary). But that's preserving a particular
algorithm; one more specific than the Platonic computation of its
Any algorithm would do, implemented on any hardware, as long as it did
the job. Ten engineers working independently on the problem would
probably come up with ten different solutions, even if they worked
with the same theoretical model of a neuron.
I suppose a Turing machine could perform the same
computation, but it would perform it very differently. And I wonder how the
Turing machine would manage perception. The organs of perception would have
their responses digitized into bit strings and these would be written to the
TM on different tapes? I think this illustrates my point that, while
preservation of consciousness under the digital neuron substitution seems
plausible, there is still another leap in substituting an abstract
computation for the digital neurons.
There is a leap involved in eliminating the hardware but the first
step is establishing computationalism: that in principal you could
replace the brain with a digital computer and preserve the mind. If
the artificial neurons work as described then doesn't that prove this?
The level of the neuron is an arbitrary one. We could instead consider
replacing volumes of brain tissue with a computer-controlled device
that replicates the I/O behaviour at the surface of the volume, where
it interfaces with normal brain tissue, and expand the size of the
volume until the whole brain is replaced. One linear processor could
then do all the work, and it wouldn't matter what processor it was (as
long as it was fast enough and had enough memory), what language the
program was written in, or even what program it was. Multiple
realisability is a basic feature of functionalism.
Also, such an AI brain would not permit slicing the computations into
arbitrarily short time periods because there is communication time involved
and neurons run asynchronously.
The whole brain could be aggregated into one computation, and a
virtual environment could run as a subroutine.
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