THE mystery behind optical illusions hides in the eyes and not deep inside the brain, according to new research.
A recent study from the University of Exeter has debunked the idea that these brain-teasers emerge from complex psychological processes.
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Instead, they’re simpler than what scientists and philosophers had initially thought.
Visual illusions are caused by limits in the way our eyes and visual neurones work, the study suggested.
In a statement, sensory evolution expert and author of the paper Dr Jolyon Troscianko said: “Our eyes send messages to the brain by making neurones fire faster or slower.
“However, there’s a limit to how quickly they can fire, and previous research hasn’t considered how the limit might affect the ways we see colour.”
Take the optical illusion above, for example.
The bar in the middle of the image is filled with just one shade of grey.
And yet, it appears lighter on the left and darker on the right due to the gradient in the background.
“This throws into the air a lot of long-held assumptions about how visual illusions work,” Troscianko said.
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But if you’re able to see through the illusion, this latest study suggests you are particularly hawk-eyed.
Troscianko added that the findings also shed light on the popularity of high-definition televisions which have become a norm in the living rooms of the 21st Century.
“Modern high dynamic range televisions create bright white regions that are over 10,000 times brighter than their darkest black, approaching the contrast levels of natural scenes,” Troscianko explained.
“How our eyes and brains can handle this contrast is a puzzle because tests show that the highest contrasts we humans can see at a single spatial scale is around 200:1.
“Even more confusingly, the neurones connecting our eyes to our brains can only handle contrasts of about 10:1.
“Our model shows how neurones 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 how our neurones are precisely evolved to use every bit of capacity.
“For example, some neurones are sensitive to very tiny differences in grey levels at medium-sized scales, but are easily overwhelmed by high contrasts.
“Meanwhile, neurones coding for contrasts at larger or smaller scales are much less sensitive, but can work over a much wider range of contrasts, giving deep black-and-white differences.
“Ultimately this shows how a system with a severely limited neural bandwidth and sensitivity can perceive contrasts larger than 10,000:1.”
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