B. Dumas, D. Lalanne, and S. Oviatt. chapter Multimodal Interfaces: A Survey of Principles, Models and Frameworks, Springer-Verlag, Berlin, Heidelberg, (2009)
R. Schäfer, S. Bleul, and W. Müller. volume 3425/2005 of Lecture Notes in Computer Science, Engineering Human Computer Interaction and Interactive Systems, page 221-223. Springer Berlin, (2005)