A BRAIN-BOGGLING optical illusion makes a static image of a black hole appear as though it's swallowing you whole, research has shown.
Nine in ten people who view the deceptive image report that the hole expands as if you're heading into a dark tunnel.
The illusion, which is new to science, was cooked up by Professor Akiyoshi Kitaoka, a psychologist at Japan's Ritsumeikan University.
Writing in a paper this week, researchers said it gives viewers "a growing sense of darkness, as if entering a space voided of light".
They added that it's likely the result of our minds being fooled into thinking we're moving into a dark area.
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As our brains the resulting loss of sight, our pupils dilate, creating the feeling that we're shifting forward or falling.
The illusion occurs regardless of the size of the image and even if it is a different colour, researchers said.
"The 'expanding hole' is a highly dynamic illusion," said Professor Bruno Laeng, who ran the experiments at the University of Oslo.
"The circular smear or shadow gradient of the central black hole evokes a marked impression of optic flow, as if the observer were heading forward into a hole or tunnel."
Professor Kitaoka is an expert in visual psychology and a well-known creator of optical illusions.
To test his latest concoction, the researchers showed it to 50 people with healthy vision between the ages of 18 and 41.
They were shown "expanding hole" images of various colours on a screen in addition to scrambled versions with no discernable pattern.
The illusion of forward motion was strongest when the pattern was black, with just 86 per cent of participants able to perceive it.
That proportion dropped to 80 per cent for coloured expanding holes.
The stronger participants rated their perception of the illusion, the more their pupils dilated during the task.
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This suggests a clear link between the illusion and the dilation of the pupils.
Optical illusions are often just a bit of fun, but they also hold real value for scientists.
The brain puzzles help researchers shed light on the inner workings of the mind and how it reacts to its surroundings.
The black hole illusion, for instance, suggests that the pupil can sometimes react to the anticipation of light as opposed to light hitting the eye.
"Here we show based on the new ‘expanding hole’ illusion that the pupil reacts to how we perceive light – even if this ‘light’ is imaginary like in the illusion – and not just to the amount of light energy that actually enters the eye," Laeng said.
"The illusion of the expanding hole prompts a corresponding dilation of the pupil, as it would happen if darkness really increased."
The research was published May 30 in Frontiers in Human Neuroscience.
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