Called a “concealed information task,” the test’s goal is ostensibly simple: identify words as they flash on a computer screen. If one of a small set of randomly selected “target” words appears, press yes. For all other words, press no. The catch, McNally said, is that while many of the words hold no meaning for the patients, a small subset of the non-target words are taken from two autobiographical questionnaires patients fill out at the start of the test — one while inhabiting one personality, the second in another.