Scientists stretch colour palette, identify a new, unseen hue, name it ‘olo’

The human eye can distinguish ten million shades of colour, it is believed. A huge palette indeed, but scientists now claim to have identified a new colour, unseen till now. 

The claim comes from a team of researchers in the United States who had laser pulses fired into their eyes. They claim that the laser stimulated the individual cells in the retina and pushed their perception beyond its natural limits, reports The Guardian.

The five people who took part in the study described it like blue-green, but not fully.
“We predicted from the beginning that it would look like an unprecedented colour signal but we didn’t know what the brain would do with it,” said Ren Ng, an electrical engineer at the University of California, Berkeley. “It was jaw-dropping. It’s incredibly saturated.”

The researchers shared an image of a turquoise square to give a sense of the colour, which they named ‘olo’, but stressed that it could only be seen following laser manipulation of the retina.

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“There is no way to convey that colour in an article or on a monitor,” said Austin Roorda, a vision scientist on the team. “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.”

Humans perceive the colours when light falls on cones, the colour-sensitive cells in the retina. The cones are three types: sensitive to long (L), medium (M) and short (S) wavelengths of light.

Natural light is a blend of multiple wavelengths that stimulate L, M and S cones in the retina to different extents and the variations are perceived as different colours. The red light stimulates L cones, while blue light activates S cones, but the M cones are in the middle and no natural light excites them alone.

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The team at Berkeley started working to overcome this limitation and began by mapping a small part of a human retina to pinpoint the positions of M cones. A laser was used to scan the retina and a tiny pulse of light was fired to stimulate the cell.

The result, published in Science Advances, is a colour in the field of vision about twice the size of a full moon. The colour is beyond the natural range of the eye as the M cones are stimulated almost exclusively, something that natural light cannot achieve. 
The colour was given the name ‘olo’ for a reason, as it denotes the binary 010, indicating that among the L, M, and S cones, only the M cones are switched on.

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The researchers’ claim has left one expert bemused. “It is not a new colour,” said John Barbur, a vision scientist at City St George’s, University of London. 
“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.” The work, he said, had ‘limited value’.

The researchers, however, believe that the tool, named Oz vision after the Emerald City in the L Frank Baum books, will assist them in probing basic science questions about how the brain creates visual perceptions of the world, and that it may have other applications. 

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The findings might give some insight to researchers about colour blindness or diseases like retinitis pigmentosa that affect vision.