  Artificial reinforcement learning (RL) is a widely used technique in
artificial intelligence that provides a general method for training agents to
perform a wide variety of behaviours. RL as used in computer science has
striking parallels to reward and punishment learning in animal and human
brains. I argue that present-day artificial RL agents have a very small but
nonzero degree of ethical importance. This is particularly plausible for views
according to which sentience comes in degrees based on the abilities and
complexities of minds, but even binary views on consciousness should assign
nonzero probability to RL programs having morally relevant experiences. While
RL programs are not a top ethical priority today, they may become more
significant in the coming decades as RL is increasingly applied to industry,
robotics, video games, and other areas. I encourage scientists, philosophers,
and citizens to begin a conversation about our ethical duties to reduce the
harm that we inflict on powerless, voiceless RL agents.
