Max Welling, Michal Rosen-zvi, Geoffrey E. Hinton
Directed graphical models with one layer of observed random variables and one or more layers of hidden random variables have been the dom- inant modelling paradigm in many research ﬁelds. Although this ap- proach has met with considerable success, the causal semantics of these models can make it difﬁcult to infer the posterior distribution over the hidden variables. In this paper we propose an alternative two-layer model based on exponential family distributions and the semantics of undi- rected models. Inference in these “exponential family harmoniums” is fast while learning is performed by minimizing contrastive divergence. A member of this family is then studied as an alternative probabilistic model for latent semantic indexing. In experiments it is shown that they perform well on document retrieval tasks and provide an elegant solution to searching with keywords.