Keeping Your Distance: Solving Sparse Reward Tasks Using Self-Balancing Shaped Rewards

TL;DR

This paper presents a simple, model-free method that uses auxiliary distance-based rewards to improve exploration and solve sparse reward tasks effectively without additional reward engineering.

Contribution

It introduces a novel auxiliary reward mechanism based on pairs of rollouts that prevents local optima and enhances learning in sparse reward environments.

Findings

Successfully solves maze navigation and 3D construction tasks.

Outperforms intrinsic curiosity and reward relabeling strategies.

Does not require domain-specific reward engineering.

Abstract

While using shaped rewards can be beneficial when solving sparse reward tasks, their successful application often requires careful engineering and is problem specific. For instance, in tasks where the agent must achieve some goal state, simple distance-to-goal reward shaping often fails, as it renders learning vulnerable to local optima. We introduce a simple and effective model-free method to learn from shaped distance-to-goal rewards on tasks where success depends on reaching a goal state. Our method introduces an auxiliary distance-based reward based on pairs of rollouts to encourage diverse exploration. This approach effectively prevents learning dynamics from stabilizing around local optima induced by the naive distance-to-goal reward shaping and enables policies to efficiently solve sparse reward tasks. Our augmented objective does not require any additional reward engineering or domain expertise to implement and converges to the original sparse objective as the agent learns to solve the task. We demonstrate that our method successfully solves a variety of hard-exploration tasks (including maze navigation and 3D construction in a Minecraft environment), where naive distance-based reward shaping otherwise fails, and intrinsic curiosity and reward relabeling strategies exhibit poor performance.