  Robot facial expressions and gaze are important factors for enhancing
human-robot interaction (HRI), but their effects on human collaboration and
perception are not well understood, for instance, in collaborative game
scenarios. In this study, we designed a collaborative triadic HRI game
scenario, where two participants worked together to insert objects into a shape
sorter. One participant assumed the role of a guide. The guide instructed the
other participant, who played the role of an actor, by placing occluded objects
into the sorter. A humanoid robot issued instructions, observed the
interaction, and displayed social cues to elicit changes in the two
participants' behavior. We measured human collaboration as a function of task
completion time and the participants' perceptions of the robot by rating its
behavior as intelligent or random. Participants also evaluated the robot by
filling out the Godspeed questionnaire. We found that human collaboration was
higher when the robot displayed a happy facial expression at the beginning of
the game compared to a neutral facial expression. We also found that
participants perceived the robot as more intelligent when it displayed a
positive facial expression at the end of the game. The robot's behavior was
also perceived as intelligent when directing its gaze toward the guide at the
beginning of the interaction, not the actor. These findings provide insights
into how robot facial expressions and gaze influence human behavior and
perception in collaboration.
