Effect of emotional expression in simple line drawings of a face on human economic behavior

In the present study, human altruistic behavior was used to measure a robot´s ability to express emotional states through facial expressions. An experimental investigation was conducted, in which human participants interacted with a humanoid robot and an LCD monitor was used to display facial expressions. A simple line drawing of a face was used to remove realistic, biological human features from the agent´s face. Participants were asked to play the ultimatum bargaining game, which is usually used to measure human altruistic behavior. All participants were assigned as the proposer and were instructed to decide their offer within one minute by controlling a slider bar. The corners of the mouth of the line drawing simply moved upward or downward depending on the position of the slider bar. The results suggest that the change of facial expressions of a simple line drawing of a face significantly affected altruistic behavior. Offers were increased by 13% by showing contingent changes of facial expression.