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Tuesday, August 29, 2000

The Cognitive Role of Dreaming

[A letter I just wrote to a mailing list]

>Since we are functionally robots, I think it would be appropriate to talk
>about robot sleep.  Perhaps though you were talking about modern-day
>non-carbon-based robots.  If sleep is defined as an animal function (as it
>now is) then we will have to redefine sleep in order to have these robots
>dream.

I imagine we've evolved to perform various functions during sleep, simply because it's there (dark, cold nights -> shut down and wait for day -> take advantage of this time to do things harder to do when we're active). Many of these will not apply to robots (no need to grow hair and fingernails--an example of something we do mostly in our sleep).

Dreaming, however, serves a very important cognitive role, which any AI would do well to employ, imho. I imagine dreams may have other functions too, but here's my theory for the primary role of dreaming:

Practice.

Yeah, sounds simple minded, but consider the details: We learn about the world in a heterarchy, putting our low-level experiences together into higher-level abstractions, and those into yet higher ones, and so on. At any given time, we have a frontier of understanding, a huge knowledge base of puzzle pieces that can potentially fit together in a myriad of ways to build more useful abstractions if only we knew what those ways were.

Enter dreaming. In a dream, we can use our current knowledge to simulate the outcome of some combination or sequence of events, and then we can observe that outcome, remember it, and hence expand our "intuitive" knowledge base to cover broader, more abstract experiences than we've actually personally had (or risked). For example, think of a rat in a new complex environment: If the rat explores the entire environment once assuming good observation and memory, he now has everything he needs to truly "know" the environment: He has visited each region and knows what regions are immediate neighbors of others. Immediate neighbors is key: except for the particular path the rat took when exploring the environment (they tend to follow the spokes of a wheel, incidentally), he only knows very short-distance correlations within the environment. But when nap time comes along, and real-world input stops coming in, the rat can now continue exploring the environment in his simulated dream world--which he can do quite robustly since he knows the local transitions--with complete impunity from physical harm, no less.

In the dream, the rat knows there's cheese up on the counter (because in his explorations, he smelled residues of it, and his past experience says there will be more to come). But how can he get there!? The original route he took was incredibly long and indirect-- too much work, and too much cat exposure. So he thinks about it, applies his best spacial-planning abilities to predict a good way to go. He leaves his imaginary home beneath the imaginary fridge, scampers across the imaginary floor... Finds himself at the base of the counter, but there's no way up from here. Looks around and feels a bit exposed -- just the sort of situation where you'd expect.... An imaginary cat! He scampers along the base of the counter, mental simulation stepping him from region to region according to the transitions he learned earlier, looking for an escape... Too late! The cat catches up with him. Reset. He runs the other direction, region to region, ah hah! Hiding nook number seven! He's safe. This will be good experience to have later! Reset back to fridge. Try hypothesis number two -- around the side, hop on the chair, hop on the table, hop to the counter, voila! Got the cheese! Reset back to fridge. Run the simulation again with random cat. And so on.

Now when the rat re-enters the real world, he knows intuitively how to get around, how to make a quick escape from all the risky areas, what areas are too risky because they have no good escapes, and so on.

Now apply the same thing to us. At any given time we only know so much, but it's enough to run simulations and learn much more. It may be very abstract: Maybe we're simulating an interaction with another human, modeling their emotional transitions, working through some problem with them. Oops! Pissed them off. Reset.

Or, maybe we're working on something very concrete: Maybe we're learning a new sport, and we've got lots of short-time experience, but can't put it all together. E.g., in wind-surfing there's this function of the angle of the sail to the water and wind vs. your weight on the boom. From the exact combination of those things, you end up somewhere else a moment later -- accelerating up or down or forward or falling back -- and this changes the angles in the next moment which leads to different effects and so on. Maybe after a day or two of getting thrown around a lot, you've got a pretty good map of short-time transitions like this. But that's a far cry from being able to get from one stable position to another, or to compensate for a big gust or chop that may require a long cycle of of transitions to bring you back to neutral. In your dreams, you can keep practicing, putting together the short-time transitions you know until you find the chain that gets you where you want.

So your dreams are your learning grounds for solving the problems you can't or haven't solved during the day--practice, practice, practice and maybe when you hit the problem head on in real-life you'll act quick and survive it or even get the cheese.

-Simon

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