  In recent years, deep artificial neural networks (including recurrent ones)
have won numerous contests in pattern recognition and machine learning. This
historical survey compactly summarises relevant work, much of it from the
previous millennium. Shallow and deep learners are distinguished by the depth
of their credit assignment paths, which are chains of possibly learnable,
causal links between actions and effects. I review deep supervised learning
(also recapitulating the history of backpropagation), unsupervised learning,
reinforcement learning & evolutionary computation, and indirect search for
short programs encoding deep and large networks.
