Two new face illusions.

The perception of human faces is different from that of other shapes: it has long been known that specialized mechanisms exist in the human visual system that, on the one hand, permit us to categorize and remember faces with remarkable accuracy, but that, on the other hand, necessarily involve heuristics that can lead to mistaken perceptions. Recently, two new illusions involving face perception have been discovered. The ‘Bogart illusion’, discovered by Pawan Sinha [Perception (2000) 29, 1005–1008], works best with a black-and-white photograph of someone looking sideways: if a negative of the image is made, the face seems to look in the opposite direction! This illusion shows that we have a specialized, modular mechanism for the socially crucial task of detecting gaze direction, which works on the assumption that the dark area is the iris. The knowledge that the iris is light instead of dark in a negative makes little or no difference: the illusion is cognitively impenetrable. The second illusion, the multiple faces phenomenon, discovered by Maria Lucia de Bustamente Simas [Perception (2000) 29, 1393–1396], can be experienced by fixating off the edge of a photograph in such a way that the blind spot falls on the nose (for example, by covering the right eye and looking at a point 10 cm to the right of the nose, with the photo about 40 cm away). After about a minute, many observers experience strange phenomena, such as seeing expression changes or a rapid succession of other, sometimes unfamiliar, faces. According to the author, this phenomenon demonstrates the workings of the inferotemporal cortex, where long-term memory traces of faces are stored. M.W.