  Two desiderata of reinforcement learning (RL) algorithms are the ability to
learn from relatively little experience and the ability to learn policies that
generalize to a range of problem specifications. In factored state spaces, one
approach towards achieving both goals is to learn state abstractions, which
only keep the necessary variables for learning the tasks at hand. This paper
introduces Causal Bisimulation Modeling (CBM), a method that learns the causal
relationships in the dynamics and reward functions for each task to derive a
minimal, task-specific abstraction. CBM leverages and improves implicit
modeling to train a high-fidelity causal dynamics model that can be reused for
all tasks in the same environment. Empirical validation on manipulation
environments and Deepmind Control Suite reveals that CBM's learned implicit
dynamics models identify the underlying causal relationships and state
abstractions more accurately than explicit ones. Furthermore, the derived state
abstractions allow a task learner to achieve near-oracle levels of sample
efficiency and outperform baselines on all tasks.
