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Grotesque face illusion
http://www.youtube.com/watch?v=wM6lGNhPujE
If you view a rapid sequence of faces they begin to look more and more grotesque. The reasons behind this shocking illusion are not well known yet, but appear to be a case of adaptation to the mean, so that small differences from the mean become exaggerated. See Tangen, J. M., Murphy, S. C., & Thompson, M. B. (2011). Flashed face distortion effect: Grotesque faces from relative spaces. Perception, 40, 628-630
Prosopagnosia
http://www.youtube.com/watch?v=vwCrxomPbtY&feature=related
A short, but moving, film showing a lady who suffers from prosopagnosia.