Tricks of the Eye

Try out these games of illusions and misperceptions on two Duke faculty websites

Tuesday, February 26, 2008

Durham, NC -- What’s in an optical illusion?

For Duke neuroscientist Dale Purves, illusions assist researchers in developing a theory of vision that explains differences between what we actually see and the visual stimuli that affect the brain. For Fuqua behavioral economist Dan Ariely, the illusions tell us about how perception affects behavior and physiology.

Both have been in the news recently: Purves, George B. Geller Professor of Neurobiology and Psychological & Brain Sciences and director of the Center for Cognitive Neuroscience, for his award-winning website and Ariely for his new book Predictably Irrational. Both approach optical illusions with different focus, but both also make it part of their research to bring their work to the general public.

They come from different disciplines, but both researchers explore the limits to the rationality of our bodies and behavior. Purves “challenges the cherished belief that our visual brains are logically organized,” according to a Duke Magazine report. His theory is that perception is “generated probabilistically, representing the most frequently observed real-world sources of the stimuli confronting the observer in the past.” In other words, when we see a tree, we see it not just because it is there, but because the visual clues we receive from it most closely fits the visual data we received from seeing other trees in the past.

Similarly, Ariely argues as an economist that we think we are making rational choices, but in fact we don’t understand the forces that affect our decision-making. Indeed, he says, we are prone to falling into perceptual traps in regular and predictable ways.

Lines and Angles

Lines and angles are another source of illusion and are part of Dale Purves' research. To find out which angles are the same, go to Purves's See For Yourself website.

Visitors to their websites are invited to play a few visual games, and here at Duke Today we thought we’d highlight those games for our readers to play. Purves’ illusions can be found here. On his “See for Yourself” website, the games he posts concerns brightness, color, lines and angles and other sensory cues. Each is accompanied by an empirical explanation for the illusion.

ariely

This Koffka ring tricks the viewer on Dan Ariely's website

Ariely’s visual illusions can be found here. He uses checkerboards and Koffka rings to also explore perception and the tricks of the eye. In his case, he’s interested in how the gap between perception and reality affects behavior. His website also invites viewers to test themselves on The Door Game, which asks gameplayers to make choices based on keeping their options open.

New York Times columnist John Tierney played the Door Game and then invited his readers to try as well.

After you challenged these tests, let us know what you think. And be prepared – these games are not what you think.