D. Raptis, N. Tselios, and N. Avouris. Proceedings of the 7th international conference on Human computer interaction with mobile devices & services, page 153-160. New York, NY, USA, ACM, (2005)
M. Roussou, E. Kavalieratou, and M. Doulgeridis. IDC '07: Proceedings of the 6th international conference on Interaction design and children, page 77--80. New York, NY, USA, ACM, (2007)