Does behavioral diversity in intrinsic rewards help exploration?

In recent years, intrinsic reward approaches have attracted the attention of the research community due to their ability to address various challenges in Reinforcement Learning, among which, exploration and diversity. Nevertheless, the two areas of study have seldom met. Many intrinsic rewards have been proposed to address the hard exploration problem by reducing the uncertainty of states/environment. Other intrinsic rewards were proposed to favor the agent's behavioral diversity, providing benefits of robustness, fast adaptation, and solving hierarchical tasks. We aim to investigate whether pushing for behavioral diversity can also be a way to favor exploration in sparse reward environments. The goal of this paper is to reinterpret the intrinsic reward approaches proposed in the literature, providing a new taxonomy based on the diversity level they impose on the exploration behavior, and complement it with an empirical study. Specifically, we define two main categories of exploration: "Where to explore'' and "How to explore''. The former favors exploration by imposing diversity on the states or state transitions (state and state + dynamics levels). The latter ("How to explore'') rather pushes the agent to discover diverse policies that can elicit diverse behaviors (policy and skill levels). In the literature, it is unclear how the second category behaves compared to the first category. Thus, we conduct an initial study on MiniGrid environment to compare the impact of selected intrinsic rewards imposing different diversity levels on a variety of tasks.