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JohnDavidBustard comments on Interesting talk on Bayesians and frequentists - Less Wrong
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Model selection is definitely one of the biggest conceptual problems in GAI right now (I would say that planning once you have a model is of comparable importance / difficulty). I think the way to solve this sort of problem is by having humans carefully pick a really good model (flexible enough to capture even unexpected situations while still structured enough to make useful predictions). Even with SVMs you are implicitly assuming some sort of structure on the data, because you usually transform your inputs into some higher-dimensional space consisting of what you see as useful features in the data.
Even though picking the model is the hard part, using Bayes by default seems like a good idea because it is the only general method I know of for combining all of my assumptions without having to make additional arbitrary choices about how everything should fit together. If there are other methods, I would be interested in learning about them.
What would the "really good model" for a GAI look like? Ideally it should capture our intuitive notions of what sorts of things go on in the world without imposing constraints that we don't want. Examples of these intuitions: superficially similar objects tend to come from the same generative process (so if A and B are similar in ways X and Y, and C is similar to both A and B in way X, then we would expect C to be similar to A and B in way Y, as well); temporal locality and spatial locality underly many types of causality (so if we are trying to infer an input-output relationship, it should be highly correlated over inputs that are close in space/time); and as a more concrete example, linear momentum tends to persist over short time scales. A lot of work has been done in the past decade on formalizing such intuitions, leading to nonparametric models such as Dirichlet processes and Gaussian processes. See for instance David Blei's class on Bayesian nonparametrics (http://www.cs.princeton.edu/courses/archive/fall07/cos597C/index.html) or Michael Jordan's tutorial on Dirichlet processes (http://www.cs.berkeley.edu/~jordan/papers/pearl-festschrift.pdf).
I'm beginning to think that a top-level post on how Bayes is actually used in machine learning would be helpful. Perhaps I will make on when I have a bit more time. Also, does anyone happen to know how to collapse URLs in posts (e.g. the equivalent of <a href=...>test </a> in HTML).
A high level post on its use would be very interesting.
I think my main criticism of the Bayes approach is that it leads to the kind of work you are suggesting i.e. have a person construct a model and then have a machine calculate its parameters.
I think that much of what we value in intelligent people is their ability to form the model themselves. By focusing on parameter updating we aren't developing the AI techniques necessary for intelligent behavior. In addition, because correct updating does not guarantee good performance (because the model properties dominate) then we will always have to judge methods based on experimental results.
Because we always come back to experimental results, whatever general AI strategy we develop its structure is more likely to be one that searches for new ways to learn (with bayesian model updating and SVMs as examples) and validates these strategies using experimental data (replicating the behaviour of the AI field as a whole).
I find it useful to think about how people solve problems and examine the huge gulf between specific learning techniques and these approaches. For example, to replicate a Bayesian AI researcher an AI needs to take a small amount of data, an incomplete informal model of the process that generates it (e.g. based on informal metaphors of physical processes the author is familiar with) and then find a way of formalising this informal model (so that its behaviour under all conditions can be calculated) and possibly doing some theorem proving to investigate properties of the model. They then apply potentially standard techniques to determine the models parameters and judge its worth based on experiment (potentially repeating the whole process if it doesn't work).
By focusing on Bayesian approaches we aren't developing techniques that can replicate these kinds of lateral and creative thinking behaviour. Saying there is only one valid form of inference is absurd because it doesn't address these problems.
I feel that trying to force our problems to suit our tools is unlikely to make much progress. For example, unless we can model (and therefore largely solve) all of the problems we want an AI to address we can't create a "Really Good Model".
Rather than manually developing formalisations of specific forms of similarity we need an algorithm to learn different types of similarity and then construct the formalisation itself (or not as I don't think we actually formalise our notions of similarity and yet can still solve problems).
Automated theorem proving is a good example where the problems are well defined yet unique, so any algorithm that can construct proofs needs to see meta patterns in other proofs and apply them. This brings home the difficulty of identifying what it means for things to be similar and also emphasises the incompleteness of a probabilistic approach: the proof that the AI is trying to construct has never been encountered before, in order for it to benefit from experience it needs to invent a type of similarity to map the current problem to the past.
But even "learning to learn" is done in the context of a model, it's just a higher-level model. There are in fact models that allow experience gained in one area to generalize to other areas (by saying that the same sorts of structures that are helpful for explaining things in one area should be considered in that other area). Talking about what an AI researcher would do is asking much more out of an AI than one would ask out of a human. If we could get an AI to even be as intelligent as a 3-year-old child then we would be more or less done. People don't develop sophisticated problem solving skills until at least high school age, so it seems difficult to believe that such a problem is fundamental to AGI.
Another reference, this time on learning to learn, although unfortunately it is behind a pay barrier (Tenenbaum, Goodman, Kemp, "Learning to learn causal models").
It appears that there is also a book on more general (mostly non-Bayesian) techniques for learning to learn: Sebastian Thrun's book. I got the latter just by googling, so I have no idea what's actually in it, other than by skimming through the chapter descriptions. It's also not available online.