The kernel for Doppel came from a piece in New Scientist about interoception—the way humans can discern the internal states of the body and conceive of it as “their own.” The idea is that our sense of self is not merely a mental process that somehow envelops the body, but somehow arises from the two-way conversation between the brain and other organs. As Manos Tsakiris, the softly spoken psychologist and neuroscientist who advises Doppel, tells me, “You cannot cut off cognition from the rest of the body, and you cannot cut off the body from the rest of the world in which you interact.” By harvesting your natural response to rhythm, Doppel runs counter to the notion that the self resides in the mind alone—that the human is a creature of the will, a maker of rational decisions, a sovereign mind bossing around dumb matter.