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Jack comments on Updating, part 1: When can you change your mind? The binary model - Less Wrong
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So I think I figured this whole thing out. Are people familiar with the type-token distinction and resulting ambiguities? If I have five copies of the book Catcher in the Rye and you ask me how many books I have there is an ambiguity. I could say one or five. One refers to the type, "Catcher in the Rye is a coming of age novel" is a sentence about the type. Five refers to the number of tokens, "I tossed Catcher in the Rye onto the bookshelf" is a sentence about the token. The distinction is ubiquitous and leads to occasional confusion, enough that the subject is at the top of my Less Wrong to-do list. The type token distinction becomes an issue whenever we introduce identical copies and the distinction dominates my views on personal identity.
In the Sleeping Beauty case, the amnesia means the experience of waking up on Monday and the experience of waking up on Tuesday, while token-distinct are type-identical. If we decide the right thing to update on isn't the token experience but the type experience: well the calculations are really easy. The type experience "waking up" has P=1 for heads and tails. So the prior never changes. I think there are some really good reasons for worrying about types rather than tokens in this context but won't go into until I make sure the above makes sense to someone.
How are you accounting for the fact that - on awakening - beauty has lost information that she previously had - namely that she no longer knows which day of the week it is?
Maybe it's just because I haven't thought about this in a couple of weeks but you're going to have to clarify this. When does beauty know which day of the week it is?
Before consuming the memory-loss drugs she knows her own temporal history. After consuming the drugs, she doesn't. She is more uncertain - because her memory has been meddled with, and important information has been deleted from it.
Information wasn't deleted. Conditions changed and she didn't receive enough information about the change. There is a type (with a single token) that is Beauty before the experiment and that type includes a property 'knows what day of the week it is', then the experiment begins and the day changes. During the experiment there is another type which is also Beauty, this type has two tokens. This type only has enough information to narrow down the date to one of two days. But she still knows what day of the week it was when the experiment began, it's just your usual indexical shift (instead of knowing the date now she knows the date then but it is the same thing).
Her memories were DELETED. That's the whole point of the amnesia-inducing drug.
Amnesia = memory LOSS: http://dictionary.reference.com/browse/Amnesia
Oh sure, the information contained in the memory of waking up is lost (though that information didn't contain what day of the week it was and you said "namely that she no longer knows which day of the week it is"). I still have zero idea of what you're trying to ask me.
If she had not ever been given the drug she would be likely to know which day of the week it was. She would know how many times she had been woken up, interviewed, etc. It is because all such information has been chemically deleted from her mind that she has the increased uncertainty that she does.
I might have some issues with that characterization but they aren't worth going into since I still don't know what this has to do with my discussion of the type-token ambiguity.
It is what was missing from this analysis:
"The type experience "waking up" has P=1 for heads and tails. So the prior never changes."
Your priors are a function of your existing knowledge. If that knowledge is deleted, your priors may change.
Makes sense to me.