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SilasBarta comments on Dreams with Damaged Priors - Less Wrong
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I think you're doing what Eliezer_Yudkowsky just warned against: how long is that hypothesis?
"The brain 'decides' to erase dream memories in such a way that we lose ~80% of our short-term memory of them and all of the long-term memory of them that we don't deliberately try to remember, on the basis of sufficient Bayes-structure in the brain, and its having observed (over period _?) the lack of entanglement between dream-based conclusions and the real world, and its prediction of sufficiently bad consequences ..."
Also, isn't that brain architecture a pretty narrow target for such a dumb process as evolution to hit? It's smart enough to exterminate dream conclusions (not to mention identify what is a dream, before you wake up) with extreme prejudice but not e.g. astrology?
FWIW, here's the theory I prefer and would defend:
"Dreams are random neuron firings" + "The feeling of dream coherency is the result of the brain's normal procedure for mapping sense data to best hypothesis."
That is indeed complicated, but that hypothesis isn't what Yvain was suggesting. The proposed adaptation is just that memories don't get stored as usual during REM sleep, which is a relatively simple thing for the brain to do. (Also, it's pretty clear that this actually happens.) It's then argued that this is a good adaptation for evolutionary reasons, because if we lacked it (and kept the rest of our tendencies of believing every conclusion we remember, context notwithstanding) we'd have some problems.
(E.g. an ex-girlfriend of mine who would stay angry at people who had been mean to her in her dreams, despite knowing that it had just been a dream.)
I don't have that bad a case, but sometimes I notice an emotions from a dream continuing into the next day. I drop them when I realize they're from a dream-- but now I realize that I only do that when something reminds me of some detail from the dream and I understand the source of the emotion. Scary thought-- how much of my emotional life is literally dream-based?
I've noticed sometimes that I think I've done something or I have something, but it was only in a dream. I worry that this will one day affect something important, rather than like last week my plan to have grilled cheese for lunch (I had already eaten all my cheddar cheese).
So Ben Folds wasn't exaggerating?
Your theory is largely consistent with Yvain's theory. Maybe it's competing for the short-term part of his theory, but your theory simply doesn't address why we dreams fade after waking up.
But I see his theory rather differently than you do: it is evolution, not the brain, that has made the observation. Of course, if dreaming is about rewriting long-term memory, then other effects on memory could be side-effects.
Yvain says the brain eliminates dreams because of a noticed property of dreams as such. My theory (not really mine, just endorsing without remembering where I first read it, but I'll keep the terminology) says that the brain is just applying normal hypothesis update procedures, with no need to identify the category "dreams".
I think it does. To wake up is to be bombarded with overwhelming evidence that one's most recent inferences ("dreams") are false. So, whatever neural mechanism (synaptic strengths + firing patterns) represented these inferences is crowded out, if not replaced outright, by a radically different one.
You might say, "But when I change my mind after believing something stupid, I remember that I used to believe it." Sure, because that belief was there much longer and developed more inertia compared to a dream, and you "self-stimulated" that belief, which, lo, helps you remember dreams too.
"But when I briefly believe something stupid and then correct it, I remember it." Compare the set of all beliefs you've held for under twenty minutes, to the set of all your dreams. Do you think you remember a higher fraction of one than the other?
I wasn't claiming Yvain left out the possibility of evolution doing the learning -- that's what I meant by "over period _?" Was this entanglement noticed over the person's life, evolutionary history (the Baldwin effect), or what? But I didn't know how to concisely say that any more clearly.
True, and that would be a parsimonious way to handle the phenomenon of dreaming, but that wasn't Yvain's theory.
That theory is too short.