The brain-bending secret behind hundreds of optical illusions has finally been revealed (2024)

The brain-bending secret behind hundreds of optical illusions has finally been revealed (1)

Scientists armed with a new computer model have taken a step closer to unlocking the mind-bending secrets of optical illusions that trick the brain into seeing the wrong colors when it's processing images.

"Simultaneous contrast illusions" are a wide-ranging group of deceptive illustrations that trick people into thinking specific parts of an image are different colors from one another, when in reality, they're the same color. The effect rests on the illustrator altering the brightness or color in the background, in order to alter our perception of objects in the foreground. For example, in the image above, the smaller bar in the middle of the image is a single gray color but appears to be a gradient of varying shades because the background is brighter at one end and darker at the other. Another example is the Munker-White illusion, displayed in the image below, in which 12 spheres appear red, purple and green but are actually the same shade of beige.

Scientists have broadly known why these illusions work for more than a century, but in all that time, experts haven't been able to agree on exactly how they trick the brain. There are two possible explanations. The first is that the illusion is created from the bottom up, starting with low-level neural activity that requires no previous exposure to this type of illusion. The second is top-down, meaning it requires higher brain functions and plays off what your brain has previously learned about the brightness and color of light over time.

In a new study, published June 15 in the journal Computational Biology, a pair of researchers used a new computer model that mimics human vision to try to settle the debate once and for all.

Related: A new type of optical illusion tricks the brain into seeing dazzling rays

The brain-bending secret behind hundreds of optical illusions has finally been revealed (2)

The model, known as the "spatiochromatic bandwidth limited model," uses computer code to mimic how the network of brain cells, or neurons, that first receive data from the eyes starts to decipher an image before that data is sent to other, "higher-level" regions of the brain to be fully processed. The model breaks down the image into sections, measures each section's brightness and then coalesces those assessments into a single report that can be sent to the brain, similar to what happens with human vision.

The beauty of this model is that the code allows the individual sections to be processed only at the same speed as human neurons could feasibly assess them, so the model is restricted to match our own visual limitations, study co-author Jolyon Troscianko, a visual ecologist at the University of Exeter in the U.K., told Live Science. "This aspect of the model is particularly novel — no one seems to have considered the effect that limited bandwidth might have on visual processing," he added. Specifically, the new model takes into account how quickly neurons can "fire," or shoot a message to other neurons in their network.

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The researchers used their new model to analyze more than 50 simultaneous contrast illusions to see if the program would also mistakenly identify specific parts of the images as being different colors, as a human being would. (It is unclear exactly how many simultaneous contrast illusions exist, but there are likely hundreds, the report authors noted.)

During these experiments, the model was consistently fooled into identifying the wrong colors, Troscianko said. "My collaborator [Daniel Osorio] kept emailing me new illusions, saying that he didn't think it would work with this one," he added. "But to our surprise and delight, it generally predicted the illusion in almost all cases."

The brain-bending secret behind hundreds of optical illusions has finally been revealed (4)

Because the model is also "tricked" by these illusions without the equivalent complex processing power of the human brain, it suggests that neither higher-order visual processing nor past experiences are required for these illusions to work. This seems to confirm the bottom-up hypothesis that says only basic-level neural processing is responsible for the images' deception, the authors concluded.

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"In essence, many illusions that were previously thought to rely on complex visual processing, or at least visual processing that requires feedback loops, can actually be explained with something as simple as a single layer of neurons," Troscianko said.

The results support similar findings from a 2020 study in the journal Vision Research. In that study, children who were born with cataracts but underwent successful cataract removal were fooled by the images shortly after regaining their sight, despite having no past visual experiences to provide context for the images.

The brain-bending secret behind hundreds of optical illusions has finally been revealed (5)

Harry Baker

Senior Staff Writer

Harry is a U.K.-based senior staff writer at Live Science. He studied marine biology at the University of Exeter before training to become a journalist. He covers a wide range of topics including space exploration, planetary science, space weather, climate change, animal behavior, evolution and paleontology. His feature on the upcoming solar maximum was shortlisted in the "top scoop" category at the National Council for the Training of Journalists (NCTJ) Awards for Excellence in 2023.

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The brain-bending secret behind hundreds of optical illusions has finally been revealed (2024)

FAQs

The brain-bending secret behind hundreds of optical illusions has finally been revealed? ›

The brain-bending secret behind hundreds of optical illusions has finally been revealed. "Simultaneous contrast illusions" rely on altering the backgrounds of images to change how we perceive the colors and brightness of objects within them. Now, a computer model may have revealed exactly how they fool us.

What is the secret behind optical illusion? ›

Your senses gather information and send it to your brain. But your brain does not simply receive this information—it creates your perception of the world. This means that sometimes your brain fills in gaps when there is incomplete information, or creates an image that isn't even there!

How is your brain tricked by optical illusions? ›

By arranging a series of patterns, images, and colors strategically, or playing with the way an object is lit, the brain can be tricked into seeing something that isn't there. How you perceive proportion can also be altered depending on the known objects that are nearby. It's not magic — it's an optical illusion.

What do optical illusions reveal? ›

Optical illusions play on the brain's biases, tricking it into perceiving images differently than how they really are. And now, in mice, scientists have harnessed an optical illusion to reveal hidden insights into how the brain processes visual information.

What are the optical illusions in mice? ›

Summary: Mice are susceptible to a visual phenomenon known as neon color spreading, commonly seen as an optical illusion in humans. The study utilized both electrophysiology and optogenetics to explore how different levels of neurons contribute to the perception of brightness.

What part of the brain do optical illusions affect? ›

One possibility is that the illusion is generated in the visual cortex. Located at the back of your head, this is the part of your brain that directly processes the information coming from your eyes.

Do you see real things in an optical illusion? ›

Optical illusions occur because our brain is trying to interpret what we see and make sense of the world around us. Optical illusions simply trick our brains into seeing things which may or may not be real.

What are the 3 main optical illusions? ›

There are three major types of illusions: cognitive illusions, literal illusions, and physiological illusions. Each of these different types of illusions have their own way of tricking the brain into misunderstanding what it is seeing.

Why are we fooled by optical illusions? ›

“This theory would suggest that visual illusions exist because brains are taking advantage of statistical regularities in the world, and in that sense, these common illusions may all be instances of the same phenomenon: brains making inferences based on the typical arrangement of the visual world.”

What is the theory behind optical illusions? ›

Sometimes, our brain gets confused by what the eyes are trying to tell it. This can mean the brain thinks things are moving when actually they're still. Or you might “see” shapes, shades or colours that aren't really there.

What animal is associated with illusions? ›

Bowerbirds provide one of the most elaborate and fascinating examples of a visual illusion that may be used to manipulate size perception. Male great bowerbirds (Ptilonorhynchus nuchalis) clear court areas for displays, which they then cover with gray objects such as stones and bones.

What is the biology behind optical illusions? ›

Using MRI scans, scientists can analyze what is happening in our brains when we look at illusions. They've learned that neurons can actually compete with one another to see light and dark spots. The winning neurons influence the message your brain gets and, therefore, what you end up perceiving [source: Hogenboom].

What is the meaning behind optical illusion? ›

Optical illusions are visual experiences that play tricks on the brain's perception. Certain neurons in the brain influence the message that the brain gets, which as a result, leads to what a person perceives. Also, the brain has a need to define reality based on objects that are familiar or that it has seen before.

Why do we get tricked by optical illusions? ›

The problem is our eyes only know a handful of words to describe what they see. Sometimes, our brain gets confused by what the eyes are trying to tell it. This can mean the brain thinks things are moving when actually they're still. Or you might “see” shapes, shades or colours that aren't really there.

What is the theory of optical illusions? ›

The theory is that a stimulus follows its individual dedicated neural path in the early stages of visual processing and that intense or repetitive activity in that or interaction with active adjoining channels causes a physiological imbalance that alters perception.

What is the physics behind optical illusions? ›

Numerous optical illusions are produced by the refraction (bending) of light as it passes through one substance to another in which the speed of light is significantly different. A ray of light passing from one transparent medium (air) to another (water) is bent as it emerges.

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