Effects of Gesture on the Perception of Psychological Anthropomorphism: A Case Study with a Humanoid Robot Maha Salem 1 , Friederike Eyssel 2 , Katharina Rohlfing 2 , Stefan Kopp 2 , and Frank Joublin 3 1 Research Institute for Cognition and Robotics, Bielefeld University, Germany, msalem@cor-lab.uni-bielefeld.de 2 Center of Excellence Cognitive Interaction Technology, Bielefeld University, Germany, {feyssel, rohlfing, skopp}@cit-ec.uni-bielefeld.de 3 Honda Research Institute Europe, Offenbach, Germany, frank.joublin@honda-ri.de Abstract. Previous work has shown that gestural behaviors affect an- thropomorphic inferences about artificial communicators such as virtual agents. In an experiment with a humanoid robot, we investigated to what extent gesture would affect anthropomorphic inferences about the robot. Particularly, we examined the effects of the robot’s hand and arm gestures on the attribution of typically human traits, likability of the robot, shared reality, and future contact intentions after interacting with the robot. For this, we manipulated the non-verbal behaviors of the humanoid robot in three experimental conditions: (1) no gesture, (2) congruent gesture, and (3) incongruent gesture. We hypothesized higher ratings on all dependent measures in the two gesture (vs. no gesture) con- ditions. The results confirm our predictions: when the robot used ges- tures during interaction, it was anthropomorphized more, participants perceived it as more likable, reported greater shared reality with it, and showed increased future contact intentions than when the robot gave instructions without using gestures. Surprisingly, this effect was particu- larly pronounced when the robot’s gestures were partly incongruent with speech. These findings show that communicative non-verbal behaviors in robotic systems affect both anthropomorphic perceptions and the mental models humans form of a humanoid robot during interaction. Keywords: Multimodal Interaction and Conversational Skills, Non-verbal Cues and Expressiveness, Anthropomorphism 1 Introduction Social robotics research is dedicated to designing, developing, and evaluating robots that can engage in social environments in a way that is both appealing and intuitive to human interaction partners. Therefore, a social robot’s behavior Acknowledgement. The work described is supported by the Honda Research In- stitute Europe.