Continual Task Allocation in Meta-Policy Network via Sparse Prompting

How to train a generalizable meta-policy by continually learning a sequence of tasks? It is a natural human skill yet challenging to achieve by current reinforcement learning: the agent is expected to quickly adapt to new tasks (plasticity) meanwhile retaining the common knowledge from previous tasks (stability). We address it by "Continual Task Allocation via Sparse Prompting (CoTASP)", which learns over-complete dictionaries to produce sparse masks as prompts extracting a sub-network for each task from a meta-policy network. By optimizing the sub-network and prompts alternatively, CoTASP updates the meta-policy via training a task-specific policy. The dictionary is then updated to align the optimized prompts with tasks' embedding, thereby capturing their semantic correlations. Hence, relevant tasks share more neurons in the meta-policy network via similar prompts while cross-task interference causing forgetting is effectively restrained. Given a trained meta-policy with updated dictionaries, new task adaptation reduces to highly efficient sparse prompting and sub-network finetuning. In experiments, CoTASP achieves a promising plasticity-stability trade-off without storing or replaying any past tasks' experiences and outperforms existing continual and multi-task RL methods on all seen tasks, forgetting reduction, and generalization to unseen tasks.