>
These trippy optical illusions baffle the best of us, as they seem to completely transform the color of an object.
But scientists have now revealed the truth about so-called ‘simultaneous contrast’ illusions – and it turns out they may not be as complicated as we originally thought.
New evidence from the University of Exeter suggests the mind-bending puzzles are a result of our limited nervous system.
This follows years of back and forth as experts have debated whether illusions stem from neural processing in the brain, the eyes or even a psychological phenomenon.
“Our eyes send messages to the brain by making neurons fire faster or slower,” says Dr Jolyon Troscianko, who co-led the study.
Experts reveal that dizzying illusions are the result of our limited neural networks. Pictured: The gray bar is a consistent shade of gray, but appears darker on the right and lighter on the left
“However, there is a limit to how fast they can fire, and previous research has not considered how the limit might affect the way we see color.”
Researchers investigated a series of illusions that appear to change the color of objects.
One image shows a gray bar against a black-to-white gradient background.
Even though the rectangular bar is a gray block color, it appears lighter on the left and darker on the right because of the gradient in the background.
This is called simultaneous contrast, where a dark environment makes targets appear brighter, and vice versa.
This phenomenon is also depicted in another image, with two rectangles over a background of black and white stripes.
Although both rectangles have the same shade of gray, they appear different, which is purely due to their position in the image.
Illusions like this demonstrate “color constancy,” which refers to our ability to perceive colors.
Scientists believe that our “limited bandwidth” of human perception can confuse color if overwhelmed by too much at once.
This is also shown in another illusion of two Rubik’s Cubes that both have what appear to be yellow and blue tiles on their top surfaces.
The ones that look yellow on the left are actually a gray color identical to the blue tiles on the right.
Taking these limits into account, experts developed a model that they believe simulates our experience of looking at patterns.
This device, known as the Spatiochromatic Bandwidth Limited (SBL) model, successfully predicted how humans perceive illusions in 35 cases.
Both rectangles appear to be different shades of gray, but they are actually the same color. This is the result of ‘simultaneous contrast’, an illusion created by a mix of contradictory colours
This is also shown in another illusion of two Rubik’s Cubes that both have what appear to be yellow and blue tiles on their top surfaces. The ones that look yellow on the left are actually a gray color identical to the blue tiles on the right
“This throws into the air a lot of long-standing assumptions about how visual illusions work,” said Dr Troscianko.
‘Our model shows how neurons with such limited contrast bandwidth can combine their signals to allow us to see these enormous contrasts, but the information is “compressed” – resulting in visual illusions.
‘The model shows exactly how our neurons have evolved to use every bit of capacity.
‘Some neurons, for example, are sensitive to very small differences in gray values at medium scales, but are quickly overwhelmed by high contrasts.
“Meanwhile, neurons encoding larger- or smaller-scale contrasts are much less sensitive, but can act across a much wider range of contrasts, creating deep black-and-white differences.”
Dr. Troscianko believes these findings shed light on the popularity of high-definition televisions.
He explained that contrasts found outdoors are most easily perceived by our brains and therefore less trippy.
“Modern high dynamic range televisions create bright white areas that are more than 10,000 times brighter than their darkest blacks, approximating the contrast levels of natural scenes,” he said.
“How our eyes and brains can handle this contrast is a mystery, because tests have shown that the highest contrasts we humans can see on a single spatial scale are around 200:1,” he said.
Now the model could be used to further explore human and animal perception, with some species varying wildly in their ‘bandwidth’ of color.
“Apart from predicting color rendering, the SBL model highlights relatively unexplored compromises in visual systems,” the authors wrote in their study, published in PLoS Computational Biology.