On Mon, May 11, 2015 at 2:14 AM, Bruce Kellett <[email protected]> wrote:
> Bruno Marchal wrote: > >> On 07 May 2015, at 14:45, Bruce Kellett wrote: >> >>> ...... >>> Now, having read this many times, and looked at the other summaries of >>> the MGA, I still feel that something crucial is missing. We go from the >>> situation where we remove more and more of the original 'brain', replacing >>> the removed functionality by the projections from the movie, which, it is >>> agreed, does not alter the conscious experience of the first person >>> involved, to the conclusion that the physical brain is entirely >>> unnecessary; indeed, irrelevant. >>> >> >> Hmm... On the contrary: the brain is necessary. It is the primitive >> physicalness of the brain which is not relevant. >> > > That is not what you say in the paper. "Hence, consciousness is not a > physical phenomenon, nor can it be a phenomenon relating to observed matter > at all." You go on to say that the appearance of matter cannot be based on > a notion of primitive matter. But these are different things. Elsewhere you > appear to agree that consciousness does depend on the observed physical > brain. In fact, it would be foolish to deny this given the weight of > physical evidence that shows this to be the case. > > Now that I have had a couple of days away from the internet to think about > this, and have read other comments on this thread, I think I understand > better the point that was not clear to me from the COMP(2013) paper. What > your intuition claims to be absurd in the MGA is that replaying the film > can instantiate consciousness. The reason for this is based on your belief > that replaying the film is not a computation, and since the basic > assumption is of comp is that consciousness is Turing emulable -- is in > fact a computation -- we cannot have consciousness without the associated > computation. > > The argument is then that if the assumption of physical supervenience > (supervenience of consciousness on a physical brain) leads to a situation > in which consciousness would appear to be supported by something (the film) > which is not a computation, then a contradiction has been reached, and the > idea of physical supervenience must be wrong (if comp is correct). > > That makes sense, but I did not previously accept this because my > intuition was not that the projection of the film would not reconstitute > the original conscious moment. The important point that is now clear, is > that you claim that projection the film does not constitute a computation, > so cannot support consciousness. I disagree with this. As Russell has > suggested, projecting the film can very well be considered to be a > computation. > It can be viewed in that way, but it is only a computation of the most trivial form: step 1: set state = X_1 step 2: set state = X_2 ... step N: set state = X_n Now if you can only introspect a computers's storage and not its program, it is not possible to differentiate this succession of states from another computer program whose memory follows the same succession of states by virtue of its computations. This is analogous to Ned Block's argument against the validity of the Turing test: 4.1 (Logically) Necessary and Sufficient Conditions <http://plato.stanford.edu/entries/turing-test/#LogNecSufCon> known as the "Block Head" argument. In the argument, an arbitrarily vast lookup table maps the history of all inputs up to a certain point to an output. Without analyzing the implementation, to an outside judge the program can of course present any level of intelligence. However it requires memory exponential to the number of inputs provided. Also, while this Blockhead program is arguably intelligent (for some finite time) I would not attribute consciousness to it, for its computation is of the most simple form. Given its answer table as a Map, the code it performs to fetch an answer would be one line of (Java) code shown below: private Map<String[], String> answerMap = ... // (making this is the hard part); public String returnAnswer(String inputs[]) { return answerMap.get(inputs); } If the above program is conscious, then perhaps most Java programs are already consciousness, for nearly all use maps. Perhaps it is conscious in some primitive way, but it stretches my credulity to believe it could manifest human level consciousness, regardless of how big or complicated the answerMap was. Jason > We have to ask what constitutes a computation in the context of this > discussion. The starting point is that part or all of the brain is > replaceable by a computer -- the brain is Turing emulable. So it seems > reasonable to define a computation as a mapping between some input and some > output that is Turing emulable. In other words, one can replace the device > that takes some input to produce some particular output with a general > Turing machine. That mapping from input to output would then be considered > a computation in the terms of the present discussion of the comp thesis. > Computation is more than a map between an input and output it is the expression of a relation or logical operation. Updating a state to some value is a computation, but you cannot use "state updates" to build any conceivable program, you need a wider instruction set and a memory that you can write things to and read things from. > > Defined in this way, it is clear that projecting the movie film on to the > physical substrate is nothing more than a general computation. The input is > a source of light directed on to the film, and the output is the image > focussed on the screen (or brain substrate). If you like, to use Russell's > terms again, the film is a program that is run through the projector as a > computer. This process is completely emulable by a Turing machine. In fact, > digital projections of moving images are routinely performed on general > purpose digital computers. The film (program) can be stored digitally, and > the light source and screen can also be realized digitally. > Computation can yield any digital movie, but the playback of any digital movie (of the same encoding) has only one program associated with it, and ignoring all the decompression algorithms, the playback program is trivial. So while a Turing machine can be used to play back any movie, any movie does not imply any computation. Jason > > The claim that the film (and projection) is not a computation is thus > false. It is a computation in exactly the same way that the brain function > replaced by a Turing machine in the "yes doctor" step 0 of the argument is > a computation. So the MGA does not establish the conclusion that > "consciousness can no longer be related to any physical phenomenon > whatsoever (i.e., brains in skulls), nor can any subjective appearance of > matter be based on a notion of primitive matter." > > In fact, the MGA seems to have very little to do directly with the > hypothesis of primitive physicality. The argument appears to be that if > physical supervenience (a different notion than primitive physicality) > leads to a contradiction with the comp hypothesis, then physical > supervenience must be abandoned. Extending this line of thinking, it > appears to be suggested that if physical supervenience is abandoned, there > is no remaining role for primitive physical matter in the understanding of > consciousness. The argument is less clear at this point, but something of > the sort seems to be implied. > > But if the notion of physical supervenience cannot be ruled out, then the > way is open for primitive physicality. The comp argument, which claims that > the appearance of the physical can be extracted from the UD running in > Platonia, has no greater claim to credence than the physicalist's claim > that mathematics is a human invention, extracted from our experience of the > physical world. > > The choice between these might reduce to nothing more than personal > preference. > > > Bruce > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. 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