AI guru Geoffrey Hinton recently gave a brilliant Google engEdu talk, "The Next Generation of Neural Networks".
If you have any interest in neural networks (or, like me, got frustrated and lost all interest in the mid-1990s), set aside an hour and watch the talk. It is well worth it.
The talk starts with a short description of the history of neural networks, focusing on the frustrations encountered, and then presents Boltzmann machines as a solution.
Geoffrey clearly is motivated by trying to imitate the "model the brain could be using." For example, after fixing the output of a model to ask it to "think" of the digit 2, he enthusiastically describes the model as his "baby", the internal activity of one of the models as its "brain state", and the output of different forms of digits it recognizes as a 2 as "what is going on in its mind."
The talk is also full of enjoyably opinionated lines, such as when Geoffrey introduces alternating Gibbs sampling as a learning method and says, "I figured out how to make this algorithm go 100,000 times faster," adding, with a wink, "The way you do it is instead of running for [many] steps, you run for one step." Or when he dismissively calls support vector machines "a very clever type of perceptron." Or when he criticizes locality sensitive hashing as being "50 times slower [with] ... worse precision-recall curves" than a model he built for finding similar documents. Or when he said, "I have a very good Dutch student who has the property that he doesn't believe a word I say" when talking about how his group is verifying his claim about the number of hidden unit layers that works best.
You really should set aside an hour and watch the whole thing but, if you can't spend that much time or can't take the level of detail, don't miss the history of NNets in the first couple minutes, the description and demo of one of the digit recognition models starting at 18:00 (slide 19), and the discussion of finding related documents using these models starting at 31:40 (slide 28).
On document similarity, it was interesting that a Googler asked a question about finding similar news articles in the Q&A at the end of the talk. The question was about dealing with substantial changes in the types of documents you see -- big news events, presumably, that cause a bunch of new kinds of articles to enter the system -- and Geoffrey addressed it by saying that small drifts could be handled incrementally, but very large changes would require regenerating the model.
In addition to handwriting recognition and document similarity, some in Hinton's group have done quite well using these models in the Netflix contest for movie recommendations (PDF of ICML 2007 paper).
On a lighter note, that is the back of Peter Norvig's head that we see at the bottom of the screen for most of the video. We get two AI gurus for the price of one in this talk.