  Reinforcement learning (RL) is a powerful tool for solving complex
decision-making problems, but its lack of transparency and interpretability has
been a major challenge in domains where decisions have significant real-world
consequences. In this paper, we propose a novel Advantage Actor-Critic with
Reasoner (A2CR), which can be easily applied to Actor-Critic-based RL models
and make them interpretable. A2CR consists of three interconnected networks:
the Policy Network, the Value Network, and the Reasoner Network. By predefining
and classifying the underlying purpose of the actor's actions, A2CR
automatically generates a more comprehensive and interpretable paradigm for
understanding the agent's decision-making process. It offers a range of
functionalities such as purpose-based saliency, early failure detection, and
model supervision, thereby promoting responsible and trustworthy RL.
Evaluations conducted in action-rich Super Mario Bros environments yield
intriguing findings: Reasoner-predicted label proportions decrease for
``Breakout" and increase for ``Hovering" as the exploration level of the RL
algorithm intensifies. Additionally, purpose-based saliencies are more focused
and comprehensible.
