In the race to build computers that can think like humans, the proving ground is one version of the Turing test — the Loebner Prize, an annual battle between the world’s most advanced artificial-intelligence programs and ordinary people.

The objective? To find out whether a computer can act “more human” than a person. In his own quest to beat the machines, author Brian Christian, serving as a judge at the contest, discovers that the march of technology isn’t just changing how we live, it’s raising new questions about what it means to be human.