Fumitaka Yamaoka Takayuki Kanda Hiroshi Ishiguro Norihiro Hagita Developing a model of robot behavior to identify and appropriately respond to implicit attention-shifting. 133-140 2009 HRI http://doi.acm.org/10.1145/1514095.1514120 conf/hri/2009 db/conf/hri/hri2009.html#YamaokaKIH09