Seeking literature on using neural networks for understanding

I just took an undergrad class on AI. We covered feed-forward neural networks but most of the material was on tuning them for better prediction results. One thing I found interesting when we developed a 3-layer net for gender classification with pictures of faces was that each of the hidden nodes ended up corresponding to very high level human-understandable features (the presence of a mustache/beard, thickness of eyebrows). Is there any good material to read about using neural networks for understanding rather than just prediction?