Nadine Pfeiffer-Leßmann Ipke Wachsmuth Formalizing Joint Attention in Cooperative Interaction with a Virtual Human. 540-547 2009 KI http://dx.doi.org/10.1007/978-3-642-04617-9_68 conf/ki/2009 db/conf/ki/ki2009.html#Pfeiffer-LessmannW09