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I'm not convinced that the function of the brain is prediction: it seems that prediction is subsidiary to defining an action policy. Prediction is only useful

I'm not convinced that the function of the brain is prediction: it seems that prediction is subsidiary to defining an action policy. Prediction is only useful for an organism inasmuch as it allows it to calculate expected future utility for actions. And these actions are the only things that lead to different outcomes in terms of evolutionary fitness, thus the actions that are ultimately output by the brain are the only things that determined its evolution. If the purpose of prediction is to calculate expected future utility of different actions, then it does not follow that a general-purpose prediction device will be useful, because the prediction device might use all its energy predicting aspects of the environment along dimensions that are irrelevant to utility. A useful prediction device would only predict along useful dimensions, and may be very different in behavior from a generalized autoencoder. As an example of this difference as it comes up in the field of deep learning, consider the case of machine translation: you could either train a sequence model (LSTM or whatever) to autoencode sequences---i.e., to be able to predict them---and then use the resulting representations to do translation, or you could train end-to-end where the objective function is translation quality. It turns out the latter yields better results. Maybe the brain, or part of the brain, is a prediction engine and another part does action selection based on the predictions. But then why would we identify intelligence with the prediction engine part rather than the two parts combined? Searching for an optimal action is a very different task than prediction; it seems you need both to have what anyone would call intelligence.

jamesrcole 9y ago
There's a danger here in getting too caught up in words (where what they're trying to capture is what matters), but can't "searching for an optional action" accurately be seen as a kind of prediction?
pazimzadeh 9y ago
You might like this TED talk, if you haven't seen it before: https://ed.ted.com/on/dcIseuAP https://ed.ted.com/on/dcIseuAP
derefr 9y ago
My current model of how the brain works comes from this helpful gloss of a very technical book, Surfing Uncertainty (http://slatestarcodex.com/2017/09/05/book-review-surfing-uncertainty/ http://slatestarcodex.com/2017/09/05/book-review-surfing-unc...), which lays out the Predictive Processing model of the brain that is (apparently) the working model for those at the vanguard of neurobiology presently. I'll try to summarize (my own layman's understanding of) the Predictive Processing theory further here, for people who don't want to read the article: As the PP theory goes, not only is the human brain a "general-purpose prediction device", but it has no other components. When we think, we're simply making predictions for the way the world will be a moment from now; and then we attempt to reconcile those predictions with the image we get of the world a moment later. In equal parts, depending on our confidence in our senses vs. our confidence in our model, we either do this by "learning" (i.e. correcting the predictions to match the signal) or by "acting" (i.e. correcting the signal to match the predictions.) The latter, "acting", is done by simply playing out the error signal (i.e. the difference between "the way the world is" and "the way the world should've been") to motor neurons, which interpret those error signals as motor commands. We seek to be less confused by the world by forcing the world to become more like our model of it! And (terminal) preferences—those are just persistent exogenous-to-the-predictive-process chemical messengers that bias neurons into outputting a different "world that should've been" than a disinterested observer, only interested in predicting, would've generated. This causes the brain's "acting" process (i.e. correcting error by changing the world) to change the world in the direction of one's preferences, rather than in the direction of one's model. In effect, brains minimize error between the world that they observe, and the world they'd like to observe. PP theory doesn't say much about where those exogenous chemicals come from, but obviously the neuroendocrine system exists, and consists of a bunch of glands that throw chemicals at the brain.
bluetwo 9y ago
To me the article read like a justification of HTM theory, which I find to be more like a cult and less like a science.

jamesrcole 9y ago

There's a danger here in getting too caught up in words (where what they're trying to capture is what matters), but can't "searching for an optional action" accurately be seen as a kind of prediction?

pazimzadeh 9y ago

You might like this TED talk, if you haven't seen it before: https://ed.ted.com/on/dcIseuAP https://ed.ted.com/on/dcIseuAP

derefr 9y ago

My current model of how the brain works comes from this helpful gloss of a very technical book, Surfing Uncertainty (http://slatestarcodex.com/2017/09/05/book-review-surfing-uncertainty/ http://slatestarcodex.com/2017/09/05/book-review-surfing-unc...), which lays out the Predictive Processing model of the brain that is (apparently) the working model for those at the vanguard of neurobiology presently. I'll try to summarize (my own layman's understanding of) the Predictive Processing theory further here, for people who don't want to read the article: As the PP theory goes, not only is the human brain a "general-purpose prediction device", but it has no other components. When we think, we're simply making predictions for the way the world will be a moment from now; and then we attempt to reconcile those predictions with the image we get of the world a moment later. In equal parts, depending on our confidence in our senses vs. our confidence in our model, we either do this by "learning" (i.e. correcting the predictions to match the signal) or by "acting" (i.e. correcting the signal to match the predictions.) The latter, "acting", is done by simply playing out the error signal (i.e. the difference between "the way the world is" and "the way the world should've been") to motor neurons, which interpret those error signals as motor commands. We seek to be less confused by the world by forcing the world to become more like our model of it! And (terminal) preferences—those are just persistent exogenous-to-the-predictive-process chemical messengers that bias neurons into outputting a different "world that should've been" than a disinterested observer, only interested in predicting, would've generated. This causes the brain's "acting" process (i.e. correcting error by changing the world) to change the world in the direction of one's preferences, rather than in the direction of one's model. In effect, brains minimize error between the world that they observe, and the world they'd like to observe. PP theory doesn't say much about where those exogenous chemicals come from, but obviously the neuroendocrine system exists, and consists of a bunch of glands that throw chemicals at the brain.

bluetwo 9y ago

To me the article read like a justification of HTM theory, which I find to be more like a cult and less like a science.