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dfranke comments on Three consistent positions for computationalists - Less Wrong
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I think that the "Mary's Room" thought experiment leads our intuitions astray in a direction completely orthogonal to any remotely interesting question. The confusion can be clarified by taking a biological view of what "knowledge" means. When we talk about our "knowledge" of red, what we're talking about is what experiencing the sensation of red did to our hippocampus. In principle, you could perform surgery on Mary's brain that would give her the same kind of memory of red that anyone else has, and given the appropriate technology she could perform the same surgery on herself. However, in the absence of any source of red light, the surgery is required. No amount of simple book study is ever going to impact her brain the same way the surgery would, and this distinction is what leads our intuitions astray. Clarifying this, however, does not bring us any closer to solving the central mystery, which is just what the heck is going on in our brain during the sensation of red.
To say that the surgery is required is a to say that there is knowledge not conveyed by third persons descriptions, and that is a problem for sweeping claims of physicalism. That is the philosophical problem, it is a problem about how successful science could be.
The other problem, of figuring out what brains do, is a hard problem, but it is not the same, because it is a problem within science.
No it isn't. All it says is that the parts of our brain that interpret written language are hooked up to different parts of our hippocampus than our visual cortex is, and that no set of signals on one input port will ever cause the hippocampus to react in the same way that signals on the other port will.
But if physicalism is correct, one could understand all that in its entirety from a third person POV, just as one can understand photosynthesis without photosynthesising. And of course, Mary is supposed to have that kind of knowledge. But you think that knowledge of how her brain works from the outside is inadequate, and she has to make changes to her brain so she can view them from the inside.
The very premise of "Mary is supposed to have that kind of knowledge" implies that her brain is already in the requisite configuration that the surgery would produce. But if it's not already in that configuration, she's not going to be able to get it into that configuration just by looking at the right sequence of squiggles on paper. All knowledge can be represented by a bunch of 1's and 0's, and Mary can interpret those 1's and 0's as a HOWTO for a surgical procedure. But the knowledge itself consists of a certain configuration of neurons, not 1's and 0's.
No, the premise of the Mary argument is that Mary has all possible book-larnin' or third person knowledge. She is specifically not supposed to be pre-equipped with experiential knowledge, which means her brain is in one of the physical states of a brain that has never seen colour.
No, she is not going to be able to instantiate a red quale through her book learning: that is not what is at issue. What is at issue is why she would need to.
Third person knowledge does not essentially change on translation from book to paper to CD, and for that matter it should not essentially change when loaded into a brain. And in most cases, we think it doesn't. We don't think that the knowledge of photosyhtesis means photsynthesising in your head. You share that the qualiaphobes assumption that there is something special about knowledge of qualia that requires instantiation.
Well, then when she steps outside, her brain will be put into a physical state that it's never been in before, and as a result she will feel enlightened. This conclusion gives us no insight whatsoever into what exactly goes on during that state-change or why it's so special, which is why I think it's a stupid thought-experiment.
It isn't intended to answer your question about neuroscience.It is intended to pose the philosopher's question about the limitations of physicalism. If physicalism is limited, that eventually folds back to your question, since one way of explaining the limitation of physicalism is that there are non-physical things going on.
When she steps outside, something physical happens in her brain that has never happened before. Maybe something "non-physical" (huh?) also happens, maybe it doesn't. We have gained no insight.
If we agree that she learns something on stepping outside we have learnt that a version of physicalism is false.
You're converting "physicalism" from a metaphysical thesis to an epistemological one, or at least adding an epistemological one. That's not the usual usage of the term.
Since qualia are widely supposed to impact physicalism, and since they don't impact ontological theses such as "everthing is material", then it is likely that people who suppose that way have the descriptive/explanatory/epistemological version in mind, however implictly.
I don't understand how Mary's room is supposed to be epistemologically relevant. Supposing that physicalism is true (and that physics is computable, for simplicity) Mary can run a simulation of herself seeing red and know everything that there is to know about her reaction to seeing red, including a comprehensive description of its phenomenology. Yet, she will still lack the subjective experience of seeing red. But this lack has nothing to do with epistemology in the first place.
It does have something to do with epistemology, because the experience delivers knowledge-by-acquaintance, which is a form of knowledge.
Yes, clearly an experience can deliver knowledge. But does experience yield any additional knowledge over a simulation of same? One could plausibly argue that it does not.