Before revision:   This categorization includes three major themes: interactive reinforcement learning, intrinsically motivated methods, and task performance-driven methods.
After revision:  Moreover, since communication capability is a prominent feature of social robots, we discuss and group the papers based on the communication medium used for reward formulation. Considering the importance of designing the reward function, we also provide a categorization of the papers based on the nature of the reward. This categorization includes three major themes: interactive reinforcement learning, intrinsically motivated methods, and task performance-driven methods.