“…Although most recent breakthroughs have been achieved with applications of supervised learning, the potential added value of unsupervised learning is so important that it is worthwhile exploring a large array of approaches. The main appeal of unsupervised learning is mostly that it is a crucial ingredient in semi-supervised learning (Weston, Ratle, & Collobert, 2008): there are many more data sources that are unlabeled than data sources that are labeled, and the volume of the unlabeled ones can be considerably larger. Similarly, better unsupervised representation learning has already been shown its advantage as a regularizer (Bengio, Lamblin, Popovici, & Larochelle, 2007;Erhan et al, 2010;Hinton, Osindero, & Teh, 2006;Le et al, 2012;Lee, Ekanadham, & Ng, 2008;Lee, Grosse, Ranganath, & Ng, 2009a;Raina, Battle, Lee, Packer, & Ng, 2007;Ranzato, Poultney, Chopra, & LeCun, 2007) and in the context of transfer learning, e.g., winning two transfer learning competitions in 2011 Mesnil et al, 2011), and domain adaptation (Glorot, Bordes, & Bengio, 2011b).…”