... as soon as I got backpropagation working, I realized--because of what we'd been doing with Boltzmann machines--that you could use autoencoders to… - Geoffrey Hinton

In late 1985, I actually had a deal with Dave Rumelhart that I would write a short paper about backpropagation, which was his idea, and he would write a short paper about autoencoders, which was my idea. It was always better to have someone who didn't come up with the idea write the paper because he could say more dearly what was important. So I wrote the short paper about backpropagation, which was the Nature paper that came out in 1986, but Dave still hasn't written the short paper about autoencoders. I'm still waiting.

Then we got very excited because now there was this very simple local-learning rule. On paper it looked just great. I mean, you could take this great big network, and you could train up all the weights to do just the right thing, just with a simple local learning rule. It felt like we'd solved the problem . That must be how the brain works. I guess if it hadn't been for computer simulations, I'd still believe that, but the problem was the noise. It was just a very very slow learning rule. It got swamped by the noise because in the learning rule you take the difference between two noisy variables--two sampled correlations, both of which have sampling noise. The noise in the difference is terrible. I still think that's the nicest piece of theory I'll ever do. It worked out like a question in an exam where you put it all together and a beautiful answer pops out.

We got quite a few applications, and one of these applications I couldn't decide if the guy was a total flake or not... He wrote a spiel about the machine code of the brain and how it was stochastic, and so the brain had this stochastic machine code. It looked like rubbish to me, but the guy obviously had some decent publications and was in a serious place, so I didn't know what to make of him... David Marr said, "Oh yes, I've met him." I said, "So what did you think of him?" David Marr said, 'Well, he was a bit weird, but he was definitely, smart." So I thought, OK, so we'll invite him. That guy was Terry Sejnowski, of course... the book was one of the first books to come out about neural networks for a long time. It was the beginning of the end of the drought... both Dave Rumelhart and Terry said that from their point of view, just getting all these people interested and in the same room was a real legitimizing breakthrough.