Robot-Specific Social Cues in Emotional Body Language Stephanie Embgen Matthias Luber Christian Becker-Asano Marco Ragni Vanessa Evers Kai O. Arras Abstract — Humans use very sophisticated ways of bodily emotion expression combining facial expres- sions, sound, gestures and full body posture. Like others, we want to apply these aspects of human communication to ease the interaction between robots and users. In doing so we believe there is a need to consider what abstraction of human social commu- nicative behaviors is appropriate for robots. The study reported in this paper is a pilot study to not offer simulated emotion but to offer an abstracted robot version of emotion expressions and an evaluation to what extent users interpret these robot expressions as the intended emotional states. To this end, we present the mobile, mildly humanized robot Daryl, for which we created six motion sequences that com- bine human-like, animal-like, and robot-specific social cues. The results of a user study (N=29) show that despite the absence of facial expressions and articu- lated extremities, subjects’ interpretation of Daryl’s emotional states were congruent with the abstracted emotion display. These results demonstrate that ab- stract displays of emotion that combine human-like, animal-like, and robot-specific modalities could in fact be an alternative to complex facial expressions and will feed into ongoing work identifying robot-specific social cues. I. Introduction As robots move from the factory floor into our homes and workplaces, they enter environments that are de- signed for humans and are inherently social by nature. To operate in everyday environments requires a human- like morphology as well as effective and intuitive ways to communicate with humans. Emotions are an important means of communication as they are able to compactly convey a great deal of information in a short time. Fong et al. [1] state in their survey that; “A socially interactive robot must send signals to the human in order to: (1) provide feedback of its internal state; (2) allow humans to interact in a facile, transparent manner.” Many robots that operate in human inhabited envi- ronments do not possess sophisticated facial or gestu- ral feature capabilities. This may be due to technical S. Embgen, M. Luber, K.O. Arras are with the Social Robotics Lab, Dept. of Computer Science, University of Freiburg, Germany. {embgens,luber,arras}@informatik.uni-freiburg.de. C. Becker-Asano is with the Dept. of Computer Science, Univer- sity of Freiburg, Germany. basano@informatik.uni-freiburg.de. M. Ragni is with the Center of Cognitive Science, University of Freiburg, Germany. ragni@cognition.uni-freiburg.de V. Evers is with the Human Media Interaction, University of Twente, the Netherlands. v.evers@utwente.nl. Fig. 1. Daryl performing the motion sequence curiosity. reasons (system complexity), economic reasons (cost- sensitivity of marketable domestic and service robots), or application-specific requirements (robots in emergency relief situations are subject to size restraints but require easy to interpret social cues to deal with injured and traumatized people). We argue that instead of mimicking intricate human affective communication, smooth human robot interac- tion requires robot-specific abstracted forms of com- munication that effectively communicate the congruent emotion and are experienced by the user as socially nor- mative. Furthermore, human morphology, even if highly sophisticated, only offers a limited number of expression modalities. Since robot morphology is synthetic, new communication modalities can be explored to assess effective robot-specific ways to communicate emotion or internal states in a manner that is socially normative and natural to users. These modalities can be inspired by nature. Animals, for instance, can communicate with their ears, smells, tails and stand up the hair of their coats. Other modalities for robots are due to technology and therefore specific to robots only, such as certain sounds, light, colors, shape, or robot-specific body parts. In this light, the issues of robot design, the conceptual- ization and design of new forms of expression, and their systematic evaluation are key questions towards effective and economically feasible socially enabled robots. A. Related Work In the attempt to give robots a humanoid shape, it appears natural to equip them with an anthropomorphic or at least zoomorphic head and face. Previous work in emotion expression for robots therefore primarily has focused on robot facial expressions [2], [3], [4], [5]. With 21 degrees of freedom the robot Kismet could 2012 IEEE RO-MAN: The 21st IEEE International Symposium on Robot and Human Interactive Communication. September 9-13, 2012. Paris, France. 978-1-4673-4606-1/12/$31.00 ©2012 IEEE 1019