Popular Science - USA (2019-10)

POPSCI.COM • WINTER 2019 109

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by Nicole Wetsman

SEEING DOUBLE

signal in

the noise

THE IMAGE ABOVE MIGHT SEEM LIKE

an arbitrary design, but amid the repeat-

ing noise is a carefully calibrated pattern.

It hides a three- dimensional object— until

it doesn’t. Hold the page close, focus as if

you’re looking through or beyond it, and

slowly move it away. What can you see?

In the 1990s, these illusions were on best-

seller lists, classroom posters, and sitcoms

like Seinfeld. But they aren’t just silly gags,

according to Jeremy Wilmer, a psychologist

at Wellesley College. The motifs are auto-

stereograms: two-dimensional pictures

that produce 3D ones thanks to our binocu-

lar vision. Each of our eyes sees a slightly

different angle on an object. When we focus

our peepers, the visual cortex fuses what

they take in and uses the differences be-

tween the views to gauge depth. Here, small

pieces of the repeating pattern are shifted

to create the so-called depth cues that give

rise to the hidden shape. At a casual glance,

the scene just looks funky. But try crossing

and uncrossing your eyes, and your noggin

will interpret parts of the image as if they’re

on different planes from one another, mak-

ing the secret figure suddenly pop out of the

page. (The answer is in the crease to the left.)

If you still can’t see it, try to relax—it could

appear when you least expect it.

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