  A key challenge in training generally-capable agents is the design of
training tasks that facilitate broad generalization and robustness to
environment variations. This challenge motivates the problem setting of
Unsupervised Environment Design (UED), whereby a student agent trains on an
adaptive distribution of tasks proposed by a teacher agent. A pioneering
approach for UED is PAIRED, which uses reinforcement learning (RL) to train a
teacher policy to design tasks from scratch, making it possible to directly
generate tasks that are adapted to the agent's current capabilities. Despite
its strong theoretical backing, PAIRED suffers from a variety of challenges
that hinder its practical performance. Thus, state-of-the-art methods currently
rely on curation and mutation rather than generation of new tasks. In this
work, we investigate several key shortcomings of PAIRED and propose solutions
for each shortcoming. As a result, we make it possible for PAIRED to match or
exceed state-of-the-art methods, producing robust agents in several established
challenging procedurally-generated environments, including a partially-observed
maze navigation task and a continuous-control car racing environment. We
believe this work motivates a renewed emphasis on UED methods based on learned
models that directly generate challenging environments, potentially unlocking
more open-ended RL training and, as a result, more general agents.
