Feb. 21 issue - Turhan Canli has an odd photo collection. It includes several shots of people's faces. He flashes photos of the words "death," "happiness" and others printed in various colors. He also has images of fanged snakes and snarling dogs, babies and white supremacists. Canli, a psychologist at the State University of New York at Stony Brook, recently showed several of the pictures to Robert Sheiman, 22, a theater manager from New Haven, Conn. Before viewing them, Sheiman was put in an fMRI scanner, and as each photo flashed up, he indicated his reaction—positive, negative or neutral—by pressing...