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July 4 2022 3:23 PM ˚
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This optical illusion has a revelation about your brain and eyes

4.1 SCI OPTICAL ILLUSION
An optical illusion from a study published in Frontiers in Human Neuroscience. Researchers found the illusion’s effect varied against different colors and was strongest when the black hole was atop a magenta background. (Photos: NYTimes)
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Do not be alarmed.

The hole you see is not really moving, growing, or expanding. The darkness will not swallow you.

This image is actually static and has much to teach us about how our brains and eyes see the world. In a study published May 30 in the journal Frontiers in Human Neuroscience, psychologists tested this illusion on 50 men and women with normal vision, and, using an infrared eye tracker, found that the greater a participant’s response to the illusion, the stronger the pupil dilation response. They also discovered that some people — perhaps even you — cannot see it.اضافة اعلان

In your eyes, the pupils subconsciously adjust to the light in your surroundings, dilating when it is dark to try to capture more light, and constricting when it is bright to prevent overexposure. When you look at this illusion, the hole is not darkening. But the perception that it darkened was enough to make your pupils respond.

“There is no reason, per se, that the pupil should change in this situation because nothing is changing in the world,” said Bruno Laeng, a psychology professor at the University of Oslo and an author of the study. “But something clearly has changed inside the mind.”

The researchers hypothesize that the illusion works because the gradient on the central hole makes it look as if the viewer is entering a dark hole or tunnel, prompting the participants’ pupils to dilate. They also found the illusion’s effect varied against different colors and was strongest when the black hole was atop a magenta background.

But not all participants were taken in by the illusion, so if you have no idea what is going on in these images, you are not alone: 14 percent of participants in the study did not report seeing it. Laeng proposes that a minority may, perhaps based on past experience, see the image in only two dimensions.

These latest results comport with a 2012 study in which Laeng and his colleagues found that the Asahi illusion, which resembles the growing glare of sunlight partly obstructed by trees or clouds, also caused people’s pupils to constrict.

The new study was “clever” for showing “a physiological indication of the response to the perceived expansion of the dark,” said Dr Dale Purves, a neurobiologist and professor emeritus who studies visual perception at Duke University. However, he said, “there are much more striking effects” that could have been used to demonstrate the pupillary response.

But this study gets at a fundamental problem all animals, including humans, deal with, Purves said. While a camera can directly measure the amount of light it is picking up, he said, “we don’t have that physical apparatus, we have no measurement of the world.”

Instead we have “an eye with a brain attached,” Laeng said. When the eye is confronted with a scene, your brain “is analyzing what it’s seeing and building up, constructing a possible scenario and adapting to it,” he said.

Another famous example is the Dress, a viral photograph that inspired spirited debates in 2015 as to whether an item of clothing was white and gold or blue and black. Laeng thinks it “is probably the greatest experiment ever in human history, so far at least.”

“The information we get from the world is quite indeterminate,” Laeng said. “The brain goes into a constant guessing mode, we have to sort of come up with the best solution, but there are several possibilities for the same type of input.”

Illusions such as the expanding hole feed into the debate over whether all perception is, fundamentally, an illusion.

“Everything we perceive is inconsistent with the physical reality of the world,” Purves said. “Everything we see, whether it’s line length, color, brightness, you name it.”

So, you are not really being tricked; instead, visual illusions help reveal what our mind’s eye is up to by showcasing mismatches between what we see and what is really out there.


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