Several people have pointed to the lack of connectivity and causality in
the separated-brain experiment as reasons to believe it is not conscious.
I think this illustrates that there are two models of consciousness
even within the functionalist/computationalist paradigm: the pattern
model, and the causal model.
In the pattern model, consciousness is associated with a certain pattern
of events, such as the pattern of neural firings in our brains.
In the causal model, consciousness is associated with a flow of information, an active processing of data. It is not enough to have neuron A fire and then neuron B fire, but rather neuron A must *cause* neuron B to fire. If we eliminate the causality, as we do in our separated brain experiment where neurons are stimulated with pre-calculated patterns, there is no consciousness.
I agree that the separated brain experiment does not pose a problem for the causal model. It is intended to challenge the pattern model.
However, I think we have seen other postings here which do challenge
the causal model. Emlyn's long message today described a scenario
(his "1'") where it is hard to say whether causality is occuring or
not. Eliezer posted a message in April which raised similar issues:
http://www.lucifer.com/exi-lists/extropians/0103.html.
The general idea here is to arrange for a brain to experience a conscious state a second time, to somehow reset it and then give it the same inputs as before. If we neglect any non-deterministic behavior, then the brain will go through exactly the same sequence of states. Each neuron's firing pattern will be exactly the same as it was during the earlier run.
However, armed with information from the earlier calculation of the same data, we can begin to blur the lines between active calculation and passive replay. Eliezer and Emlyn have both given examples of this, very similar in flavor. You run the calculation, but instead of taking the output from the previous neuron and sending it to the next one, you instead substitute that neuron's recorded output from the previous run - which will be exactly the same!
Now what are we doing? Are we actively processing data, or passively replaying the results from the previous run? How can it make a difference when we are substituting an identical recorded signal for a calculated signal? These thought experiments pose difficulties for the causal model.
Those who prefer this model and don't find the separated brain experiment to pose a challenge should take a look at Eliezer's and Emlyn's puzzles and see whether they are as easy to resolve.
Hal