Who says science isn't fun? Visual illusions, such as the dozens you will find in this special issue, make great eye candy. But they also serve a serious purpose for researchers. How? Illusions push the mysterious and wondrous brain into revealing its secrets.

From the confusing and fragmentary inputs gathered by our senses, our brains create our seemingly fluid conscious perceptions and a sensible narrative of the world around us. Brains do not, however, talk to us about how they perform those impressive tasks. Scientists can learn a lot by using imaging equipment and by making other observations. But sometimes they also have to “trick” brains, the better to probe perception. That's where illusions come in.

“It is a fact of neuroscience that everything we experience is actually a figment of our imagination,” write Susana Martinez-Conde, director of the Laboratory of Visual Neuroscience at the Barrow Neurological Institute in Phoenix, and Stephen L. Macknik, director of the Laboratory of Behavioral Neurophysiology at Barrow, in “The Neuroscience of Illusion,” starting on page 4. “Although our sensations feel accurate and truthful, they do not necessarily reproduce the physical reality of the outside world.” Martinez-Conde and Macknik, whose articles fill this special edition, study these disconnects between reality and perception for clues about the brain's operations. On the following pages you will learn, among other things, about “impossible” figures, 3-D visualization and kinetic illusions in op art.

Want more? Martinez-Conde is president of the Neural Correlate Society, which runs the annual Best Illusion of the Year Contest, sponsored by the Mind Science Foundation and Scientific American. This year's event took place on May 10 at the Philharmonic Center for the Arts in Naples, Fla.; attendees select the winners. For full details and to see articles and illusions by past winners, go to http://illusioncontest.neuralcorrelate.com.