1. Sturm, J.: On the usability of multimodal interaction for mobile access to information services. PhD thesis, Radboud University Nijmegen, Nijmegen, The Netherlands (2005)
2. Larsen, L.B.: Assessment of spoken dialogue system usability - what are we really measuring? In: Eurospeech 2003, pp. 1945–1948 (2003)
3. Naumann, A., Wechsung, I.: Developing Usability Methods for Multimodal Systems: The Use of Subjective and Objective Measures. In: Proceedings of the International Workshop on Meaningful Measures: Valid Useful User Experience Measurement (VUUM), pp. 8–12 (2008)
4. Bolt, R.A.: “Put-that-there”: Voice and gesture at the graphics interface. In: Proceedings of the 7th Annual Conference on Computer Graphics and interactive Techniques (1980)
5. Cohen, P.R., Johnston, M., McGee, D., Oviatt, S., Pittman, J., Smith, I., Chen, L., Clow, J.: QuickSet: multimodal interaction for distributed applications. In: Proceedings of the Fifth ACM international Conference on Multimedia (1997)