How to cheat on your next eye test

Next time your at the Department of Motor Vehicles renewing your driver's license, don't be surprised if you see people in the lobby staring into spinning spirals just before they take their eye test.

Why? It turns out an old favorite illusion, referred to as the "expanding motion effect," can induce increased visual acuity. This illusion is demonstrated in the Exploratorium's "Depth Spinner" Science Snack. It's a perennial favorite among visitors to our ExploratoRio Open House event.

In any case, researchers at the Universities of Glasgow and York incorporated use of the illusion with eye chart tests.

The team discovered that visual acuity—the ability to see fine detail—can be enhanced by an illusion known as the ‘expanding motion aftereffect’. While under its spell, viewers can read letters that are too small for them to read normally.

When participants stare at the center of a spinning pattern that spirals inward for about 30 seconds, shifting their view to a stationary object will induce the illusion that the static object is expanding.

Participants who started with normal visual acuity and saw [inward spinning] spirals ... showed improved visual acuity.

It's as it they were looking through a camera and zooming in on the smallest letters in the eye chart.

It is important that the spiral is spinning inward. Staring at an outward spinning spiral induces a shrinking effect.

Those who saw [outward spinning] spirals ... actually performed worse after exposure to the spirals.

Anyone who's enjoyed this illusion knows the effect is temporary.

But don’t throw out your eyeglasses just yet: the researchers note that the overall boost to visual acuity is small and fleeting.

I would not have expected this outcome. Hat tip to Richard Wiseman's appearance on Skeptics' Guide to the Universe. The Sun ran an article with the obligatory animated spinner.