  Hierarchical reinforcement learning (HRL) provides a promising solution for
complex tasks with sparse rewards of intelligent agents, which uses a
hierarchical framework that divides tasks into subgoals and completes them
sequentially. However, current methods struggle to find suitable subgoals for
ensuring a stable learning process. Without additional guidance, it is
impractical to rely solely on exploration or heuristics methods to determine
subgoals in a large goal space. To address the issue, We propose a general
hierarchical reinforcement learning framework incorporating human feedback and
dynamic distance constraints (MENTOR). MENTOR acts as a "mentor", incorporating
human feedback into high-level policy learning, to find better subgoals. As for
low-level policy, MENTOR designs a dual policy for exploration-exploitation
decoupling respectively to stabilize the training. Furthermore, although humans
can simply break down tasks into subgoals to guide the right learning
direction, subgoals that are too difficult or too easy can still hinder
downstream learning efficiency. We propose the Dynamic Distance Constraint
(DDC) mechanism dynamically adjusting the space of optional subgoals. Thus
MENTOR can generate subgoals matching the low-level policy learning process
from easy to hard. Extensive experiments demonstrate that MENTOR uses a small
amount of human feedback to achieve significant improvement in complex tasks
with sparse rewards.
