How This Illusion Makes You Think You’re Entering a Tunnel

Photo credit: Akiyoshi Kitaoka
Photo credit: Akiyoshi Kitaoka
  • Psychologists used illusions that mimic darkness and sunlight to see how viewers’ eyes reacted.

  • Most people experienced the sense of movement into darkness and their pupils dilated. Their pupils contracted while looking at the sun illusion.

  • These studies show that our brains react in anticipation of what will happen next; Our pupils expand or dilate, accordingly.


Once in a while, an optical illusion fools you in a such a sneaky way, it makes your eyes do something you’re not aware of.

Look at the image at the top of this story—a black hole surrounded by black dots. Does it feel like the blackness is expanding?

Now, let’s switch gears. How about the bright yellow image below? Does it remind you of anything?

Photo credit: Akiyoshi Kitaoka
Photo credit: Akiyoshi Kitaoka

If you were to have a friend hold a mirror close to your eyes as you view each of these images, you might notice that the yellow-and-white image causes your pupils to constrict; The black-and-white one causes them to dilate.

👁 Science is on our side. We’ll help you understand it all.

That’s because the yellow image, called the Asahi illusion, resembles the glare of sunlight surrounded by foliage. Even though the center is no brighter than the other white parts of your screen, your mind unconsciously believes it is bright like the sun, and your pupils constrict accordingly.

A similar psychological reaction is at work when you see the black hole. The gradient effect from the central darkness enhances the effect of entering a tunnel with no light.

Psychologists at the University of Oslo in Norway tested the black-hole illusion on 50 people with normal vision. Most of the men and women who reported a response to the illusion also experienced pupil dilation. With the help of an infrared eye tracker, the study authors found that people who had a stronger sense of rushing into a tunnel experienced greater pupil dilation. They published their work last month in the journal Frontiers in Human Neuroscience. This study is consistent with 2012 work from the same research team, which examined reactions to the Asahi illusion.

“If one assumes that the illusion creates an impression of moving toward a totally dark space, that would be something we are very familiar with, like entering a tunnel or a dark room. For the pupil response, this is also crucial, since moving into darkness is potentially dangerous (one cannot see),” Bruno Laeng, a psychology professor at the University of Oslo and an author of the study, tells Popular Mechanics. The study also looked at people’s responses when the black hole illusion had a colored background, even beating the white background for effectiveness.

Photo credit: Akiyoshi Kitaoka
Photo credit: Akiyoshi Kitaoka

With the perceived movement into a dark tunnel, viewers expect a change in illumination, so their pupils dilate. In everyday life, your pupils expand and contract without your knowledge, responding to different levels of brightness. In the dark, they dilate to let in more light and allow you to see better. In bright light, they contract so your eyes aren’t overexposed.

Essentially, your brain is constantly trying to anticipate what’s next, using visual cues like color and light intensity, according to the study. For example, moving into a colored space is less problematic than entering a dark, black space, since color still indicates some light by which to see, Laeng explains. But there could be a variety of factors, including past experiences, guiding our perception, according to the study.

“Perhaps the main point is that our oculomotor system controlling the eyes adjust to what we think we see, not what is really out there. In other words, they do not work as a camera, which adjusts according to a photometer, measuring light,” Laeng explains.

Don’t worry if you don’t feel a sense of movement when you stare at these illusions. The study found that these tricks don’t fool all minds. Twenty percent of the 50 study participants who viewed the black hole image didn’t have the sensation that the blackness was expanding, nor did they have a pupilary response, Laeng says. It’s possible that past experiences may influence these viewers to see the image in only two dimensions, the study authors hypothesize. But they don’t really have a specific answer yet for why these disparities exist.

“It was surprising that a sizable minority did not experience the illusion,” Laeng says. “We also did not expect that the difference between the dark holes and the colored ones would be so clear-cut, though we did predict a difference.”

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