S. Stellmach, L. Nacke, and R. Dachselt. ETRA '10: Proceedings of the 2010 Symposium on Eye-Tracking Research & Applications, page 109--112. Austin, Texas, ACM, (March 2010)
L. von Ahn, R. Liu, and M. Blum. CHI '06: Proceedings of the SIGCHI conference on Human Factors in
computing systems, page 55--64. New York, NY, USA, ACM Press, (2006)