Do you see green the same way that I see green? Every now and then, we find ourselves wondering such questions, as we have all come to know and agree on the use of generic colour names like blue, yellow, green, and so on to distinguish and analyze life around us. Surely, we are all unique in the way we view colours to a degree, but at the end of the day, green is green, and so we leave it at that. But not everyone is quite like this.
After searching for more than 25 years, neuroscientists in the UK have come across a woman who has an extra type of cone cell — the receptor cells that detect colour — in her eyes. This means she can see a whopping 99 million more colours than the rest of us, and belongs to a very small group of people with super-vision called “tetrachromats.”
The majority of humans, referred to as “trichromats,” have three types of cone cells in their eyes, with each one thought to be able to distinguish around 100 shades. Together, our three cone cells can distinguish roughly 1 million different colours. Those who are colour blind, however, only have two functioning types of cone cells.
And then there’s the doctor in northern England who researchers found two years ago. Identified as cDa29, she has four cone cell types, which means she may be able to distinguish up to 100 million colours that many of us could only fantasize about.
So how do you get a fourth type of cone cell? The idea was first proposed in 1948, when Dutch scientist HL de Vries discovered something interesting about the eyes of colour blind people. He noticed that colour blind men only possessed two normal cone cells and one mutant cone that’s less sensitive to either green or red light, while the mothers and daughters of said men possessed one mutant cone and three normal cones. This means they had four types of cone cells, one of which wasn’t working like the rest.
But it wasn’t until the 1980s, when John Mollon from Cambridge University started searching for women who might have four functioning cone cells, that interest in the phenomenon started gaining traction. Mollon suggested that, if colour blind men pass this fourth cone cell onto their daughters, then around 12 percent of the female population should be tetrachromats. Nevertheless, Mollon’s tests found that the women could only perceive the same colours as the rest of us.
In 2007, however, neuroscientist Gabriele Jordan from Newcastle University in the UK took a different approach to discovering this super-vision. She observed 25 women with a fourth type of cone cell in a dark room. She had them look into a light device, with three coloured circles of light flashing before their eyes. One of the women tested, cDa29, differentiated the three different coloured circles in every test.
“I was jumping up and down,” Jordan said. “We now know tetrachromacy exists,” she continued. “But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.”
Jay Neitz, a vision researcher at the University of Washington, believes it may require practice along with specially designed hues to truly unlock the power of tetrachromats.
“Most of the things that we see as coloured are manufactured by people who are trying to make colours that work for trichromats,” he explained. “It could be that our whole world is tuned to the world of the trichromat.”
While further study is needed, and Jordan’s results must still be replicated and verified, if the existence of tetrachromats can be confirmed, it has the potential to aid scientists in creating more advanced artificial sensing devices, as well as help us figure out more about how vision works.