An optical illusion new to science has an amazing effect on most people: watching it makes them feel like they're entering a tunnel or falling into a hole. Researchers have an explanation for the phenomenon.
A mind-boggling optical illusion developed by scientists makes viewers feel as if they are entering a tunnel or falling into a hole. The "expanding hole" illusion was invented by the Japanese Akiyoshi Kitaoka. He is a psychologist at Ritsumeikan University in Kobe. A study published in the journal Frontiers in Human Neuroscience found that the effect is felt by 86 percent of people.
"The 'expanding hole' is a highly dynamic illusion: the blurred circle or shadow progression of the central black hole gives a distinct optical flow impression, as if the observer is driving into a hole or a tunnel," explains Bruno Laeng, professor at the faculty in Psychology from the University of Oslo and first author of the study, according to the journal.
But why is this effect perceived at all? "The illusion of the 'expanding hole' causes the pupils to dilate, just as they would if the darkness were actually increasing," says Laeng. This shows that the amount of light energy that actually enters the eye is not the sole cause of the reaction of the human pupil. "Rather, the eye tunes into perceived and even imaginary light, not simply physical energy." Researchers in the field of psychosociology study optical illusions like these in order to understand the complex processes involved in the visual perception of the world.
Laeng and his colleagues also experimented with different colored holes and tested them on human subjects. It turned out that the deception was most effective when the hole was black. However, not all people seem to feel the same way: 14 percent of the participants did not perceive any illusory expansion when the hole was black, while 20 percent did not when the hole was colored. Among those who perceived expansion, the subjective strength of the deception varied widely.
The researchers don't yet know why a minority of people seem reluctant to the "expanding hole" deception. It is also unclear whether other vertebrate species, or even non-vertebrate animals with camera eyes, such as squid, perceive the same illusion as humans.