The secret to training AI might be knowing how to say "good job"

It's tough to appreciate how efficient at learning humans really are. From just a few experiences, we can figure out complex tasks like learning to walk or becoming pros at the office coffee machine (roughly of equal importance). But we haven't been able to give machines that same gift. Reinforcement learning, a promising sector of AI research where algorithms test different ways to accomplish a task until they can reliably get it right, is one method used to get machines to learn by doing. The field's biggest problem: What's the best way to tell AI it has done something right?