There's no general way to have a "none of the above" hypothesis as part of your prior, because it doesn't make any specific prediction and thus you can't update its likelihood as data comes in. See the discussion with Cyan and others about NOTA somewhere around here.
Well then I guess I would hypothesize that solving the problem of a universal prior is equivalent to solving the problem of NOTA. I don't really know enough to get technical here. If your point is that it's not a good idea to model humans as Bayesians, I agree. If your point is that it's impossible, I'm unconvinced. Maybe after I finish reading Jaynes I'll have a better idea of the formalisms involved.
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