The hollow face illusion

The hollow face illusion illustrates the power of what cognitive psychologists call “top-down” (essentially, knowledge-driven) influences on perception. Our statistically salient experience with endless hordes of convex faces in daily life installs a deep expectation of convexness: an expectation that here trumps the many other visual cues that ought to be telling us that what we are seeing is a concave mask.


From
Do Thrifty Brains Make Better Minds?
By Andy Clark
http://opinionator.blogs.nytimes.com/2012/01/15/do-thrifty-brains-make-better-minds/