As both a tiny person in the country of Brobdingnag and a giant on the island of Lilliput, Lemuel Gulliver—the protagonist of Jonathan Swift’s Gulliver’s Travels—experiences firsthand that size is relative. When we cast a neuroscientific light on this classic book, it is clear to us that Swift, a satirist, essayist, and poet, knew a few things about the mind, too. Absolute size is meaningless to our brain: we gauge size by context. The same medium-sized circle will appear smaller when surrounded by large circles and bigger when surrounded by tiny ones, a phenomenon discovered by the German psychologist Hermann Ebbinghaus. Social and psychological contexts also cause us to misperceive size. Research shows that spiders appear larger to people who suffer from arachnophobia than to those who are unafraid of bugs, and that men holding weapons seem taller and stronger than men who are holding tools. Here we present a collection of illusions that will expand your horizons and shrink your confidence in what is real. Try these out for size!
DYNAMIC SIZE CONTRAST ILLUSION
BY GIDEON CAPLOVITZ AND RYAN MRUCZEK
UNIVERSITY OF NEVADA, RENO, AND SWARTHMORE COLLEGE, U.S.A.
2013 FINALIST
This illusion shows that a viewer’s perception of an object’s size radically varies as a function of background motion. When the background is growing, the object appears to shrink. Conversely, when the background is shrinking, the object appears to grow. Caplovitz and Mruczek’s discovery suggests that our visual system integrates multiple sources of sensory information to determine the perceived size of an object. For example, the brain must consider the projected size of the object’s image on the retina as well as its size relative to other objects in the scene. Extracting the information from the visual image is particularly challenging when the object is in motion, and doubly so when the observer’s eyes pursue the moving object. One reason that might help explain why the Dynamic Size Contrast Illusion is so powerful is that items that move draw our attention more forcefully than stationary ones. Our own research showed that during magic performances, spectators tend to focus their attention on fluidly moving elements, such as the magician’s hand, instead of the parts of the stage that remain still. In the Dynamic Size Contrast Illusion, our attention may focus preferentially on the moving background, maximizing our perception of the differences between the background and the object in the foreground. See a dynamic demonstration of this illusion at the Best Illusion of the Year Contest website.
THE DYNAMIC EBBINGHAUS ILLUSION
BY CHRISTOPHER BLAIR, GIDEON CAPLOVITZ, AND RYAN MRUCZEK
UNIVERSITY OF NEVADA, RENO, U.S.A.
2014 FIRST PRIZE
Earlier we mentioned the classic Ebbinghaus Illusion, in which a circle surrounded by smaller circles looks bigger than the same circle surrounded by larger circles. This perceptual phenomenon proves that our experience of an object’s size is relative to its visual context. Blair, Caplovitz, and Mruczek created an Ebbinghaus Illusion on steroids by combining it with the principles behind the Dynamic Size Contrast Illusion. The new and improved Ebbinghaus effect consists of a dynamic display with surrounding circles that expand and shrink while the central circle’s size stays constant. The authors explained that the Dynamic Ebbinghaus Illusion is at least twice as strong as the original, static Ebbinghaus Illusion.
The illusion is even more powerful when you look at it from the corner of your eye, rather than directly. The reason could be that your peripheral vision is more sensitive to motion than your central—also called foveal—vision.
Your retina has a high-resolution central area called the fovea. The fovea sees an extremely small part of our visual field—just 0.1 percent, or the size of your thumbnail at arm’s length—but its function is critical for everyday life, and particularly so for investigating fine details and small objects. Without a fovea, you wouldn’t be able to read the newspaper, watch TV, drive a car, or interpret facial expressions.
The main reason you make eye movements is to target your fovea to the right place at the right time, a necessary condition to see in detail. Many of the neural calculations that control and direct your gaze rely on information from the non-foveal 99.9 percent of your visual field: the retinal periphery.
The periphery of your retina—though it produces lower-resolution vision than the fovea—has certain special abilities that help you to decide where to look next. For example, the periphery detects motion and gross details better than the fovea, and is more sensitive to flickering light and changes in brightness and contrast. This is the reason why fluorescent lighting sometimes flickers when you see it out of the corner of your eye, but not if you look at the light fixtures directly. So it should come as no surprise that the brain circuits processing peripheral visual information are susceptible to special kinds of illusions, especially those that involve motion and other dynamic changes. See this illusion in action at the Best Illusion of the Year Contest website.
BY PETER THOMPSON
UNIVERSITY OF YORK, U.K.
2010 FINALIST
The Fat Face Thin Illusion shows two photographs that are identical, although the upside-down face appears strikingly slimmer than the right-side-up version. One possible explanation is that it is easier for the brain to recognize distinctive facial features, such as chubby cheeks, when they are viewed in the normal upright position. Research has shown that face-selective neurons of the human brain respond best to upright faces—perhaps because there has been no evolutionary pressure to recognize faces upside-down. These same neurons may encode various facial properties—like chubbiness—and be less capable of doing so accurately when faces are upside-down. If so, all upside-down faces could end up looking more similar to one another than if they were upright.
BY KAZUNORI MORIKAWA AND ERI ISHII
OSAKA UNIVERSITY, JAPAN
2012 FINALIST
The two Barack Obama portraits above are identical except that the one on the left has a wider jaw and fuller face than in reality. The top of the head appears fatter, too, but it is not. The Head Size Illusion demonstrates that the brain does not determine the size of visual stimuli in isolation from one another; it considers objects and features in relation to those nearby in the scene. The illusion occurs in everyday life, Morikawa said, and offers an opportunity for those who wish to alter their appearance. “If one part of your face or body appears wider or thinner than average, other parts appear wider or thinner, too,” he explained. “You can take advantage of such illusions to make yourself look better, using effective makeup and clothing.”
