L. Lucignano, F. Cutugno, S. Rossi, and A. Finzi. Proceedings of the 15th ACM on International Conference on Multimodal Interaction, page 197–204. New York, NY, USA, Association for Computing Machinery, (2013)
A. Nguyen, and W. Wobcke. Proceedings of the 10th international conference on Intelligent user interfaces, page 137--144. New York, NY, USA, ACM, (2005)