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Best Visual Illusions of 2009

from New Scientist

Every visual illusion - from the way that simple lines drawn on paper seem to form a cube, to the logic-defying labyrinths of M. C. Escher - works exactly the same way: they expose discrepancies between physical reality and our perception of that reality.

That makes visual illusions appealing objects of study for neuroscientists: they offer clues to how our brains handle the information we receive about the outside world, in particular how we process visual images. "In most cases, we don't know how they work or why they work in neural terms," says Susana Martinez-Conde, a perceptual neuroscientist at the Barrow Neurological Institute in Phoenix, Arizona.

That's why a panel of scientists - of whom Martinez-Conde is one - organise the Visual Illusion of the Year Contest. Now in its fifth year, it features dozens of illusions created by scientists, artists, computer programmers and even the occasional magician. New illusions offer potentially new insights on the workings of the human mind: but they're fun, too. You can try out some of the winning entries for yourself.