Perception of Emotional Expression of Mobile Humanoid Robot Using Gait-Induced Upper Body Motion

Humans can express their emotions with not only facial expressions or gestures but also whole-body motion, even while walking, which are essential for our interpersonal relationships and our interaction with others. Communication with people is also considered an important task for robots, however emotional expressions by wheeled mobile humanoid robots when moving has not been well studied. In this paper, we implemented emotional human-like gait-induced upper body motion in a mobile android ibuki. We hypothesize that the gait-induced upper body motion with vertical oscillation enhances the human perception of a mobile robot's emotional expressions. ibuki is a mobile robot, which has a vertical oscillation mechanism, which enables the robot to move its body with a human gait-induced upper body motion. We ran two experiments in which participants watched videos of ibuki moving in a room expressing different emotions - anger, happiness, and sadness-, before answering how they perceived the emotion and their respective confidence level in their answer. Our results show that for motions with vertical oscillation, recognition rates were: 56.0 % for anger, 77.7 % for happiness, and 97.0 % for sadness. We also found that the recognition rate and confidence level of motions expressing happiness with vertical oscillation were higher. Our results play an important role in opening up avenues for more natural ways of interaction between humans and robots. For example, by approaching humans closer while expressing emotions, a robot can naturally provide an opportunity to get started conversation with them.