by STEPHEN L. MACKNIK and SUSANA MARTINEZ-CONDE
As both the midget in the country of Brobdingnag and the giant on the island of Lilliput, Lemuel Gulliver—the protagonist of Jonathan Swift’s Gulliver’s Travels—experienced firsthand that size is relative. As we cast a neuroscientific light on this classic book, it seems 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 German psychologist Hermann Ebbinghaus. Social and psychological context also causes us to misperceive size. Recent 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. In this article, we present a collection of illusions that will expand your horizons and shrink your confidence in what is real. Try them out for size!
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Full Moon
The full moon rising on the horizon appears to be massive. Hours later, when the moon is high overhead, it looks much smaller. Yet the disk that falls on your retina is not smaller for the overhead moon than it is for the rising moon. So why does the overhead moon seem smaller? One answer is that your brain infers the larger size of the rising moon because you see it next to trees, hills or other objects on the horizon. Your brain literally enlarges the moon to fit the context. Look for this effect the next time you see the moon in real life.
Scientific American for more