In 1917, working alone in a remote Swiss asylum, psychiatrist Hermann Rorschach devised an experiment to probe the human mind. For years he had grappled with the theories of Freud and Jung while also absorbing the aesthetic of a new generation of modern artists. He had come to believe that who we are is less a matter of what we say, as Freud thought, than what we see. Rorschach himself was a visual artist, and his test, a set of ten carefully designed inkblots, quickly made its way to America, where it took on a life of its own. The test was also given to millions of defendants, job applicants, parents in custody battles, workers applying for jobs, and people suffering from mental illness -- or simply trying to understand themselves better. And it is still used today. Damion Searls draws on unpublished letters and diaries, and a cache of interviews with Rorschach's family, friends, and colleagues, to tell the story of the test's creation, its controversial reinvention, and its endurance -- and what it all reveals about the power of perception.