There’s a new optical illusion in town and people can’t seem to get enough of it. A new joint study by researchers in Japan and Norway has found that 86pc of people who stare at a new ‘expanding hole’ image are able to perceive the movement associated with the illusion.

The study, a collaboration between Ritsumeikan University in Osaka, Japan and the University of Oslo in Norway, is an example of how human perception of the world around eyes through our eyes is based on predictions made by our brains.

Published in the Frontiers in Human Neuroscience journal earlier this week, the study found that many participants who were made to stare at a black spot in the centre of an image full of black dots in a white background felt like the black spot was expanding.

Some even reported feeling like they were falling into a black hole – meaning that it was not movement in the image that they perceived, but in themselves.

Although a completely static image, the illusion prompts a viewer’s pupils to expand without any change in lighting. This shows that the illusion, and the human perception of movement in it, causes a physical reaction in the body even when the mind is aware of the image being static.

The team, led by authors Bruno Laeng, Shoaib Nabil and Akiyoshi Kitaoka, asked observers to rare the magnitudes of illusory motion or expansion of the black holes – and these predicted the degree of dilation of the pupil, measured using an eye-tracker.

When the ‘holes’ were light-emitting colours such as white, staring at the image was found to constrict the pupils. “Subjective expansions were also weaker compared with the black holes,” the study noted, meaning that physical responses were most potent with black holes.

Evolution

The study also included the ‘Asahi’ illusion in which a flower-like structure is drawn on a white background in a way that gives the impression the white in the centre of the image is brighter than the white in the surrounding areas.

Pupils of people staring into the centre of the image contracted once again, meaning that even though it is not brighter than the white in the background, our brain’s perception of brightness cause a physical reaction in the body.

“The visual system is prepared from individual experience (or that of the species) with the natural statistics of the visual world, to the specific ecological condition of seeing sunlight through leaves or clouds,” the study noted.

“In fact, brightness illusions like Asahi bear a geometric resemblance to the gradients shaped by the glare of strong sunlight when partially occluded by plant leaves or cloud formations.”

Humans have evolved to ensure that a sudden change in brightness does not incapacitate vision by involuntarily constricting pupils when light is perceived to be bright.

“Radiant energy of electromagnetic radiations from both natural and artificial light sources can lead to injuries, if strong or prolonged, to the retina or other ocular structures,” the study went on.

The black hole illusion is not the first time people have fallen for a trick using colour. An exhibit at the Serralves Museum in Porto in 2018 called Descent Into Limbo by Anish Kapoor saw a man literally fall into an 8-foot hole because the black paint made it look like the surface was flat.

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