According to Daily Mail
, an ordinary person can perceive a million different hues of colors. The power to distinguish the hues comes from cells in our eyes called cones. In the average person, there are three types of cones each of which is triggered by different wavelengths of light.
explains that most people have three types of cones, and are said to be "trichromats." Color blind individuals have only two types of cones and they are said to be "dichromats." Almost all animals, including dogs and New World Monkeys are dichromats.
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However, scientists have long believed that there are people with four cones who can see a wider range of colors than most of us can detect. These persons are called "tetrachromats," and can see a hundred million colors. From the perspective of such people, the hues familiar to trichromats fracture further into more subtle shades of differences that have not been given names since most of us are trichromats who cannot see these shades and name them.
Jordan and her colleagues have for 20 years searched for people endowed with super color vision, or tetrachromatic vision. According to Discover Magazine
, Jordan found a tetrachromat two year ago. Although the person is the first tetrachromat known to science, the researchers believe there are others.
reports that Jordan and her team found many people with four types of cones but only one person passed the tests for tetrachromatic vision. The woman, identified as subject cDa29, is a doctor living in northern England. Jordan and her colleagues believe there may be other persons with tetrachromatic vision.
Jordan told Discover Magazine
that she was very excited by her discovery. It took 20 years to search for her to identify the first true tetrachromat. But a question immediately arose: Why is it that there are people with four cones who apparently do not exhibit tetrachromatic vision?
Jordan said: "We now know tetrachromacy exists. But we don't know what allows someone to become functionally tetrachromatic, when most four-coned women aren't."
The first evidence that tetrachromats might exist came in 1948, Discover Magazine
reports. A paper on color blindness written by the Dutch scientist HL de Vries, investigated color blind men who possess two normal cones and a mutant cone that is less sensitive to either green or red. This makes it difficult for such people to distinguish the two colors. De Vries incidentally tested the daughters of one of the color blind men and found that they could detect a wider range of hues of red than average persons. He found that while the color blind men had two normal cones and one mutant cone, the mothers and daughters of the color blind men had a mutant cone and three normal cones, that is, a total of four cones. He believed that the extra cone explained whey the women seemed able to distinguish a wider variety of hues of red. But De Vries did not have the opportunity to investigate the phenomenon further.
John Mollon of Cambridge University became interested in tetrachromacy in the 1980s. Jordan who was working with Mollon, concluded that since color blindness or dichromacy is common, then tetrachromacy should also be common. She estimated that about 12 percent of women are tetrachromats. The researchers selected for their study mothers of color blind men who had three normal cones and one mutant cone, and tested them for the variety of hues they could detect. But the women showed no signs of ability to detect a greater variety of colors than ordinary persons. This led to the conclusion that the fourth mutant cone was inactive in these women.
According to Discover Magazine
, in 2007, Jordan, now at Newcastle, developed more powerful methods for identifying women with tetrachromatic vision. She chose 25 women all of whom had a fourth cone and tested them for tetrachromatic vision. She identified one woman tagged cDa29, who got all questions designed to detect an extended range of color vision correct. Jordan told Discover Magazine
: “I was jumping up and down." After 20 years of search she had finally found a true tetrachomat.
reports that Jay Neitz, vision researcher at the University of Washington, believes that all women with four cones have potential for tetrachromatic vision but most need to develop or awaken the ability. Neitz said: “Most of the things that we see as colored are manufactured by people who are trying to make colors that work for trichromats. It could be that our whole world is tuned to the world of the trichromat.”
Neittz also suggested that the natural environment may not have sufficient hues of colors to harness the full potentials of tetrachromatic vision. He said that people with four cones may be helped to develop full tetrachromatic vision if they regularly visit a lab where they are exposed to vision experiences that will help then develop the cognitive skills to identify a richer variety of hues.
An intriguing question that arose was: How does cDa29 see the world? She was unable to communicate her experience to the researchers in much the same way as it is impossible to describe the experience of red to a dichromatic person. Jordan says: “This private perception is what everybody is curious about. I would love to see that.”