Researchers have shown that a startling optical illusion can trick the brain into believing that a stationary black hole is expanding.
The “widening gap” illusion, which is new to science, was created by Professor Akiyoshi Kitaoka, a psychologist at Ritsumeikan University in Kobe, Japan.
In tests, 86 percent of volunteers saw the central black hole expand, as if it were moving into a dark environment like a tunnel, or falling into a hole. The image is so good at tricking our brain that it induces pupils to dilate, just as it would if we really were. We move to a dark area.
Take a look at this picture. Do you realize that the central black hole is expanding, as if you were moving through a dark environment, or falling into a hole? Researchers say the ‘widening gap’ is a new illusion for science
How does the illusion work?
The “widening aperture illusion” shows the expansion of a central black hole, as if the viewer were moving into a dark environment, or falling into a hole.
A circular central black hole evokes an impression of optical flow – a test of motion through what we see.
According to the researchers, when people see the image, the pupil tends to dilate (enlarge) as a way to let in more light.
This happens when we realize that we are regarding to enter a dark place, such as when we are in a car regarding 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.
Professor Bruno Linge, who conducted the experiments in the Department of Psychology at the University of Oslo, said the “widening gap” is a very dynamic illusion.
The circular smear or shadow gradient of a central black hole evokes a clear impression of optical flow, as if the observer is heading forward toward a pit or tunnel.
Professor Kitaoka, who created the image, is known as the creator of optical illusions, including the famous spinning snakes illusion and the “Asahi” brightness illusion. The Asahi illusion has a central area that appears brighter than its white background, although it is 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 were shown the image, as well as several variations of the image in different colors, for a few seconds on a computer screen.
The infrared eye tracker recorded pupil dilation and contractions while viewing different images. For each one, participants were asked to subjectively rate how strong their perception of the illusion was.
As controls, participants were also shown “mixed” versions of images of the dilated apertures, with equal lighting and color, but without any pattern.
The researchers found that the illusion was most effective when the hole was black – only 14 percent of the participants did not perceive the illusion in this condition.
Meanwhile, a slightly higher percentage didn’t see the hole if it was colored – 20 percent for all colours, on average.
The researchers also found that black holes promoted strong reflexive dilation of the participants’ pupils, while colored holes caused their pupils to constrict.
For black holes, but not for colored holes, the more robust individual participants subjectively rated their illusion perception, the greater the diameter of their pupil change.
Among those who recognized the expansion, the intrinsic strength of the illusion differed, although it is uncertain what exactly caused this.
It is possible that other species of vertebrates, or even invertebrate animals with “camera-type” eyes such as octopuses, might perceive the same delusion.
Octopus eyes focus through movement, like the lens of a camera or telescope, rather than changing shape like the lens in the human eye.
The study results were published in Frontiers in Human Neuroscience.
