J. Väyrynen, L. Lindqvist, and T. Honkela. Proceedings of the International Joint Conference on Neural Networks (IJCNN 2007), page 1031--1036. Orlando, Florida, USA, (2007)
M. Johnson, T. Griffiths, and S. Goldwater. Human Language Technologies 2007: The Conference of the North American Chapter of the Association for Computational Linguistics; Proceedings of the Main Conference, page 139--146. Rochester, New York, Association for Computational Linguistics, (April 2007)