**The wake-sleep algorithm for unsupervised neural
networks**

Geoffrey E. Hinton, Peter Dayan,

Brendan J. Frey and Radford M. Neal

Department of Computer Science

University of Toronto

**Abstract**

We describe an unsupervised learning algorithm for a
multilayer network of stochastic neurons. Bottom-up 'recognition' connections convert the
input into representations in successive hidden layers and top-down 'generative'
connections reconstruct the representation in one layer from the representation in the
layer above. In the 'wake' phase, neurons are driven by recognition connections, and
generative connections are adapted to increase the probability that they would reconstruct
the correct activity vector in the layer below. In the 'sleep' phase, neurons are driven
by generative connections and recognition connections are adapted to increase the
probability that they would produce the correct activity vector in the layer above.

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*Science, 268, 1158-1161. (1995)*

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