Mind's eye

Look: This black hole illusion reveals an innate evolutionary instinct

Akiyoshi Kitaoka

Take a close look at the black hole in the center of this image.

Akiyoshi Kitaoka

Did the hole seem to expand as you gazed at it?

For most people, this illusion shows an ever-growing void and invokes a feeling that you may be about to enter a tunnel.

Akiyoshi Kitaoka

Shutterstock

But the image isn’t actually moving at all.

Instead, it’s playing a trick on your eyes, causing them to physically adjust to take in what they’re seeing.

In a report published last month in Frontiers in Human Neuroscience, researchers from Norway and Japan studied the effects of this illusion on 50 participants.

Akiyoshi Kitaoka

They presented several variations of the image to see which ones produced the strongest illusion.

Akiyoshi Kitaoka

For example, here’s the hole on a cyan background. Does the black hole effect seem more intense here than on the white background?

Akiyoshi Kitaoka

How about on a magenta background?

Akiyoshi Kitaoka

Unexpectedly, the magenta background created the strongest illusion for most people.

Jonathan Knowles/Photodisc/Getty Images

Overall, the participant’s pupils consistently dilated when they saw the black hole against any lighter-colored background.

Akiyoshi Kitaoka

For an inverted version with holes of lighter colors, the opposite is true: The pupils shrank to take in less light.

A similar phenomenon was observed in previous research on the Asahi illusion, where pupils shrank in response to the bright hole in the center.

Akiyoshi Kitaoka/Frontiers in Human Neuroscience

So why do the pupils respond to still images like this?

It might be due to an evolutionary instinct that prevents our eyes from becoming overwhelmed by a sudden influx of light or darkness, the researchers write.

Erik Von Weber/The Image Bank/Getty Images

Akiyoshi Kitaoka

Though the holes are not actually getting larger, the brain thinks they are and tries to prepare itself to not get caught off guard by what could be a sudden change in light.

But if you can’t see the holes expanding at all, don’t fret — 14 percent of the study participants couldn’t, either.

Akiyoshi Kitaoka

Akiyoshi Kitaoka

Study co-author Bruno Laeng told The New York Times that this could be due to the fact that some perceive the illusion as two dimensional, based on their past experiences.