Think you’ve seen it all?
Not so, according to a team of American researchers who say they’ve discovered a colour that’s never been seen by the human eye before.
It’s a bold claim, considering estimates that the typical human eye can distinguish around 10 million colours.
But scientists at the University of California say the new colour — which they’ve named “olo” — is a blue-green hue with an “unprecedented saturation” that sits outside the range of what the human eye can usually see, and can only be stimulated by firing laser pulses into the eye.
“There is no way to convey that colour in an article or on a monitor,” Austin Roorda, a vision scientist on the team, told The Guardian about the groundbreaking claim. “The whole point is that this is not the colour we see, it’s just not. The colour we see is a version of it, but it absolutely pales by comparison with the experience of olo.”
This image reflects the colour researchers say is the closest match to the colour seen in olo.
Ren Ng / University of California
The findings, published in the journal Science Advances on Friday, have been described by the study’s co-author, Prof. Ren Ng from the University of California, as “remarkable.”
Using an experimental technique called “Oz,” researchers say they stimulated the human retina such that people saw a brand-new colour. A laser beam was shone into the pupil of one eye of each of the study’s five participants, each who have normal colour vision. (It’s worth noting that three of the participants were also co-authors of the study.)
The human eye typically perceives colour through a combination of signals that are activated when intensities of natural light reach three types of cone cells in the eye — S, M and L cones — which are sensitive to blue, green and red light. Normal colour vision relies on the brain to interpret the signals across the retina, unlocking colour perception.
The group of researchers wondered what would happen if they could cut out the wavelengths that the L and S cones react to and exclusively activate the M cones, which are most sensitive to green.
Using the Oz system, they used laser light to only target participants’ M cone, leaving the S and L cones unaffected, and claim the five participants were treated to a colour that doesn’t exist in nature.
“By activating only the M cones, we elicited a colour beyond the natural human gamut,” the researchers wrote.
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Ng told the BBC that olo is “more saturated than any colour you can see in the real world,” and explained how a new colour could even come to be perceived.
“Let’s say you go around your whole life and you see only pink, baby pink, a pastel pink,” he said. “And then one day you go to the office and someone’s wearing a shirt, and it’s the most intense baby pink you’ve ever seen, and they say it’s a new colour and we call it ‘red.’”
Outside experts, however, have called the findings “open to argument” and a “matter of interpretation.”
Prof. John Barbur, a vision scientist at City St. George’s, University of London, explained to the BBC that “if, for example, the red cone cells (L) were stimulated in large numbers, people would ‘perceive a deep red,’ but the perceived brightness may change depending on changes to red cone sensitivity, which is not unlike what happened in this study.”
“It is not a new colour,” Barbur told The Guardian. “It’s a more saturated green that can only be produced in a subject with normal red-green chromatic mechanism when the only input comes from M cones.” He told the outlet that the American team’s findings had “limited value.”
Ng, however, says his team’s research could help them study and treat colour blindness or diseases that affect vision, but admits it’s not a colour that laypeople, en masse, will be exposed to in the near future.
“This is basic science,” said Ng. “We’re not going to see olo on any smartphone displays or any TVs any time soon. And this is very, very far beyond VR headset technology.”
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