Social Functions of Machine Emotional Expressions

Virtual humans and social robots frequently generate behaviors that human observers naturally see as expressing emotion. In this review article, we highlight that these expressions can have important benefits for human-machine interaction. We first summarize the psychological findings on how emotional expressions achieve important social functions in human relationships and highlight that artificial emotional expressions can serve analogous functions in human-machine interaction. We then review computational methods for determining what expressions make sense to generate within the context of interaction and how to realize those expressions across multiple modalities, such as facial expressions, voice, language, and touch. The use of synthetic expressions raises a number of ethical concerns, and we conclude with a discussion of principles to achieve the benefits of machine emotion in ethical ways.