Vision scientist Stuart Anstis of the University of California, San Diego, created this illusion in 2005 to celebrate the 25th anniversary of the Thatcher illusion. Anstis reasoned that if face-neurons prefer right-side up face-features, they should also be selective for other evolutionarily stable aspects of faces. He tested this idea by comparing positive and negative images of Tony Blair. Because we have evolved to see faces only in positive contrast, it follows that the perception of individual face-features should fail if shown in negative. As with the Thatcher illusion, manipulating the whole face (as in panel A) made it less recognizable than the normal face (in panel C). Using positive images of the mouth and eyes overlaid on a negative face doesn’t look particularly grotesque either (as in panel B). But a positive image of Blair with negative mouth and eyes is just as horrid as the upside-down mouth and eyes in the right-side up Thatcher (previous slide, lower-right).