Scientists create mind-blowing ‘black hole’ optical illusion

A stunning optical illusion can trick the brain into thinking a static black hole is expanding, researchers have shown.

This “expanding hole” illusion, new to science, was created by Professor Akiyoshi Kitaoka, a psychologist at Ritsumeikan University in Kobe, Japan.

During the tests, 86% of the volunteers perceived that the central black hole grew larger, as if it moved through a dark environment such as a tunnel, or fell into a hole.

The image is so good at tricking our brains that it causes the pupils to dilate, as would happen if we really moved through a dark area.

According to the researchers, when people see the image, the pupil tends to dilate (widen) to let in more light.

It happens when we become aware that we are about to enter a dark space, like when we are in a car that is about to enter a dark tunnel.

The illusion also occurs regardless of the size of the image, even if it is very small, and also if it is of a different color.

“The ‘expanding hole’ is a highly dynamic illusion,” said Professor Bruno Laeng, who led the experiments at the University of Oslo’s Department of Psychology.

“The circular smear or gradient shadow of the central black hole evokes a strong sense of optical flow, as if the viewer is heading toward a hole or tunnel.”

Professor Kitaoka, who created the image, is well known as a creator of optical illusions, including the famous spinning snakes illusion and the ‘Asahi’ illusion of light.

The Asahi illusion has a central region that looks brighter than its white background, even though it’s the same white all over.

To test the effectiveness of the new image, the researchers recruited 50 people with healthy vision between the ages of 18 and 41.

All volunteers viewed the image, as well as several variations of the image with different colors, for a few seconds on a computer screen.

An infrared eye tracker recorded the constrictions and dilations of the pupils as the different images were presented.

For each, participants were asked to subjectively rate how well they perceived the illusion.

As controls, the participants also received “blurred” versions of the expanding hole images, with equal luminance and color, but without any pattern.

The researchers found that the illusion was more effective when the hole was black – only 14% of participants did not see the illusion in this case.

Meanwhile, a slightly higher percentage didn’t see the hole if it was in color – 20% for all colors, on average.

The researchers also found that the black holes promoted strong reflex dilations of the participants’ pupils, while the colored holes caused their pupils to constrict.

For black holes, but not colored holes, the more individual participants subjectively rated their perception of the illusion, the more their pupil diameter tended to change.

Among those who perceived an expansion, the subjective strength of the illusion differed, although it is unclear why exactly.

It’s possible that other vertebrate species, or even non-vertebrate animals with camera-like eyes, such as octopuses, perceive the same illusion.

Octopus eyes focus through movement, much like the lens of a camera or telescope, rather than changing shape like the lens of the human eye.

The results of the study have been published in the journal Frontiers of Human Neuroscience.