Facial Expressions Increase Emotion Recognition Clarity and Improve Warmth and Attractiveness on a Humanoid Robot without Adding the Uncanny Valley

With the rising impact of social robots, research on understanding user perceptions and preferences of these robots gains further importance, especially for emotional expressions. However, research on facial expressions and their effects on human-robot interaction has had mixed results. To unpack this issue further, we investigated users’ emotion recognition accuracy and perceptions when interacting with a social robot that displayed emotional facial expressions or not in a storytelling setting. In our experiment, twenty-eight participants received verbal feedback either with or without facial expressions from the robot. Participants showed a significant recognition accuracy effect for emotions and significantly higher clarity for disgust, happiness, and surprise in the facial expression condition than in the no facial expression condition. In addition, participants rated Milo with facial expressions significantly higher than Milo without facial expressions in warmth and attractiveness. No significant differences were found among the rating scores of naturalness. The results from the present study indicated the importance of facial expressions when considering design choices in social robots.