Status-quo policy gradient in Multi-Agent Reinforcement Learning

Individual rationality, which involves maximizing expected individual returns, does not always lead to high-utility individual or group outcomes in multi-agent problems. For instance, in multi-agent social dilemmas, Reinforcement Learning (RL) agents trained to maximize individual rewards converge to a low-utility mutually harmful equilibrium. In contrast, humans evolve useful strategies in such social dilemmas. Inspired by ideas from human psychology that attribute this behavior to the status-quo bias, we present a status-quo loss (SQLoss) and the corresponding policy gradient algorithm that incorporates this bias in an RL agent. We demonstrate that agents trained with SQLoss learn high-utility policies in several social dilemma matrix games (Prisoner's Dilemma, Matching Pennies, Chicken Game). To apply SQLoss to visual input games where cooperation and defection are determined by a sequence of lower-level actions, we present GameDistill, an algorithm that reduces a visual input game to a matrix game. We empirically show how agents trained with SQLoss on GameDistill reduced versions of Coin Game and Stag Hunt learn high-utility policies. Finally, we show that SQLoss extends to a 4-agent setting by demonstrating the emergence of cooperative behavior in the popular Braess' paradox.