Hierarchical Reinforcement Learning (HRL) is a promising approach to solving long-horizon problems with sparse and delayed rewards. Many existing HRL algorithms either use pre-trained low-level skills that are unadaptable, or require domain-specific information to define low-level rewards. In this paper, we aim to adapt low-level skills to downstream tasks while maintaining the generality of reward design. We propose an HRL framework which sets auxiliary rewards for low-level skill training based on the advantage function of the high-level policy. This auxiliary reward enables efficient, simultaneous learning of the high-level policy and low-level skills without using task-specific knowledge. In addition, we also theoretically prove that optimizing low-level skills with this auxiliary reward will increase the task return for the joint policy. Experimental results show that our algorithm dramatically outperforms other state-of-the-art HRL methods in Mujoco domains. We also find both low-level and high-level policies trained by our algorithm transferable.

This is an interesting approach and seems novel in the context of options, although it looks to have some similarities to potential based reward shaping, e.g. (Devlin and Kudenko, 2012). The main advantages claimed for HAAR are (loosely) those of improved performance under sparse rewards and the learning of skills appropriate for transfer. These claims could be made more explicit, and that might help to justify the experimental section. The authors define advantage as: A_h(s_t h,a_t h) E[r_t h \gamma_h V_h(s_{t k} h) - V_h(s_{t} h)] The meaning of this is a little ambiguous and I would prefer this to be clarified.

The paper presents HAAR - a hierarchical reinforcement learning approach that is based on the idea of using the advantage / temporal difference error of the high-level controler provide the reward signal for the lower layer. The reviewers judged this approach to be novel, and empirical results are promising. Analytical results provide improvement guarantees similar to a base algorithm like TRPO. Several areas for improvement were mentioned, and many of these were addressed in the rebuttal. For example, the reviewers were pleased to see the additional experiment showing performance from random skill initialization.

Hierarchical Reinforcement Learning (HRL) is a promising approach to solving long-horizon problems with sparse and delayed rewards. Many existing HRL algorithms either use pre-trained low-level skills that are unadaptable, or require domain-specific information to define low-level rewards. In this paper, we aim to adapt low-level skills to downstream tasks while maintaining the generality of reward design. We propose an HRL framework which sets auxiliary rewards for low-level skill training based on the advantage function of the high-level policy. This auxiliary reward enables efficient, simultaneous learning of the high-level policy and low-level skills without using task-specific knowledge.

Hierarchical Reinforcement Learning (HRL) is a promising approach to solving long-horizon problems with sparse and delayed rewards. Many existing HRL algorithms either use pre-trained low-level skills that are unadaptable, or require domain-specific information to define low-level rewards. In this paper, we aim to adapt low-level skills to downstream tasks while maintaining the generality of reward design. We propose an HRL framework which sets auxiliary rewards for low-level skill training based on the advantage function of the high-level policy. This auxiliary reward enables efficient, simultaneous learning of the high-level policy and low-level skills without using task-specific knowledge.