Example trials from Experiment 1. a) Trial from the pigmentation condition in which shape remains constant. The six faces have been put into the correct order, with the face that is most similar to the highlighted target face at the far left, the least similar face at the far right, and so forth in between. b) Trial from the shape condition in which pigmentation remains constant. The six faces are shown in the order that they appeared initially to the subjects, and hence have not yet been placed in the correct order. Notice that shape here refers not only to the outline of the face, but also to the shapes and locations of the internal features (eyes, eyebrows, nose, mouth).