The claim that consciousness is fame in the brain, and the claim that qualia are incommunicable because of complexity are somewhat contradictory, because what is made famous in the brain can be subjectively quite simple, but remains incommunicable.
A visual field of pure blue, or a sustained note of C#, is not fundamentally easier to convey than some complex sensation. Whilst there maybe complex subconscious processing and webs of association involved in the production of qualia, qualia can be simple as presented to consciousness. The way qualia seems is the way they are, since they are defined as seemings. And these apparently simple qualia are still incommunicable, so the problem of communicating qualia is not the problem of communicating complexity.
Something that is famous in the brain needs to have a compelling quality, and some qualia, such as pains have that in abundance. However, others do not. The opposite of blindsight — access consciousness without phenomenal consciousness — is phenomenal consciousness without access consciousness, for instance "seeing something out of the corner of ones eye. Not only are qualia not uniformally compelling, but one can have mental content that is compelling, but cognitive rather than phenomenal, for instance an obsession or idée fixe; .
"And if someone did know enough about color to explain all the associations that it has, well, having associations explained to you isn't normally enough for you to make the same associations in the same way yourself, "
To some physicalists, it seems obvious that a physcial description of brain state won't convey what that state is like, because it doesn't put you into that state. Of course, a description of a brain state won't put you into a brain state, any more than a description of photosynthesis will make you photosynthesise. But we do expect that the description of photosynthesis is complete, and actually being able to photosynthesise would not add anything to our knowledge. We don't expect that about experience. We expect that to grasp what the experience is like, you have to have it. If the 3rd-person description told you what the experience was like, explained it experientially, the question of instantiating the brain-state would be redundant. The fact that these physicalists feel it would be in some way necessary means they subscribe to some special, indescribable aspect of experience even in contradiction to the version of physicalism that states that everything can be explained in physicalese.Everything means everything — include some process whereby things seem differnt from the inside than they look from the outide. They still subscribe to the idea that there is a difference between knowledge-by-aquaintance and knowledge-by-description, and that is the distinction that causes the trouble for all-embracing explanatory physicalism.
Weaker forms of physicalism are still posible, however.
"can say that when I've read articles about how echolocation works, and what sorts of things it reveals or conceals, I've felt like I know a tiny bit more about what it's like to be a bat than I did before reading the articles."
But everyone has the experience of suddenly finding out a lot more about something when they experience it themselves. That is what underpins the knowledge-by-acquaintance versus knowledge-by-description distinction.
I think this does get at one of the key issues (and one of the places where Hume was probably wrong, and Dennett constitutes genuine progress). On my theory, qualia are not simple. If qualia are by definition simple (perhaps for your reason that they seem that way, and by definition are how they seem), then I am a qualia skeptic. Simple qualia can't exist. But there is independent reason for being skeptical of the idea that phenomenal conscious experiences are as simple as they appear to be. Indeed, Hume gave an example of how problematic it is to trust our intuitions about the simplicity of qualia in his discussion of missing blue, though of course he didn't recognize what the problem really was, and so was unable to solve it.
Yesterday, as a followup to We are not living in a simulation, I posted Eight questions for computationalists in order to obtain a better idea of what exactly my computationalist critics were arguing. These were the questions I asked:
I got some interesting answers to these questions, and from them I can extract three distinct positions that seem consistent to me.
Consistent Position #1: Qualia skepticism
Perplexed asserted this position in no uncertain terms. Here's my unpacking of it:
"Qualia do not exist. The things that you're confused about and are mistaking for qualia can be made clear to you using an argument phrased in terms of computation. When you talk about consciousness, I think I can understand your meaning, but you aren't referring to anything fundamental or particularly well defined: it's an unnatural category."
The internal logic of the qualia skeptic's position makes sense to me, and I can't really respond to it other than by expressing personal incredulity. To me, the empirical evidence in support of the existence of qualia is so clear and so immediate that I can't figure out what you're not seeing so that I can point to it. However, I shouldn't need to bring you to your senses (literally!) on this in order to convince you to reject Bostrom's simulation argument, albeit on grounds completely different than any I've argued so far. If you don't buy that there's anything fundamental behind consciousness, then you also shouldn't buy Bostrom's anthropic reasoning in which he conjures up the reference class of "observers with human-type experiences"; elsewhere he refers to "conscious experience" and "subjective experience" without implication that he means anything more specific. That's taking an unnatural category and invoking it magically. In the statement that we are something selected with uniform probability from that group, how do you make sense of "are"?
Consistent Position #2: Computation is implicit in physics
This position is my best attempt at a synthesis of what TheOtherDave, lessdazed, and prase are getting at. It's compatible with position #1, but neither one entails the other.
To understand this position, it is helpful, but not necessary, to define the laws of physics in terms of something like a cellular automaton. Each application of the automaton's update rule can be understood as a primitive operation in a computation. When you apply the update rule repeatedly on cells nearby each other, you're building up a more complex computation. So, "consciousness is just computation" is equivalent in meaning, essentially, to "consciousness is just physics".
This position more-or-less necessitates answering "algorithms" to question #5, or if not that then at least something similar to RobinZ's answer. If you say "functions" then you at least need to explain how to reify the concepts of "input" and "output". You can pull this off by saying that the update rules are the functions, the inputs are the state before the rule application, and the outputs are the state afterward. Any other answer probably means you're taking something closer or identical to position #3 which I'll address next. This comment by peterdjones and his followups to it provide a (Searlesque) intuition pump showing other reasons why a "functions" reply is problematic.
I have no objection to this position. However, it does not imply substrate independence, and strongly suggests its negation. If your algorithmic primitives are defined at the level of individual update-rule applications, then any change whatsoever to an object's physical structure is a change to the algorithm that it embodies. If you accept position #2 while rejecting position #1, then you may actually be making the same argument that I am, merely in different vocabulary.
Consistent Position #3: Computation is reified by physics
I was both shocked and pleased to see zaph's answer to question #6, because it bites a bullet that I never believed anyone would bite: that there is actually something fundamental in the laws of physics which defines and reifies the concept of computation in a substrate-independent fashion. I can't find any inconsistency in this, but I think we have good reason to consider it extremely implausible. In the language of physics which is familiar to us and has served us well — the language whose vocabulary consists of things like "particle" and "force" and "Hilbert space" — the Kolmogorov complexity of a definition of an equivalence relation which tells us that an AND gate implemented in a MOSFET is equivalent to an AND gate implemented in a neuron is equivalent to an AND gate implemented in desert rocks, but is not equivalent to an OR gate implemented in any of those media — is enormous. Therefore, Solomonoff induction tells us that we should assign vanishingly low probability to such a hypothesis.
I hope that I've fairly represented the views of at least a majority of computationalists on LW. If you think there's another position available, or if you're one of the people I've called out by name and you think I've pigeonholed you incorrectly, please explain yourself.