Do Women see More Colors than Men?


Roses are red, violets are blue; or are they? The colors you see may not always be the same someone else sees. The average human can perceive one million different colors, but researchers suspect that a small percentage of women may be capable of seeing one hundred times that amount.

Women have always doubted this; now a new study has confirmed that men have a far higher chance of struggling to tell the difference between hues*, as one in 12 of them are color blind compared to one in 255 women. Researchers at Newcastle University also believe that some women may be able to see 99 million more colors than the average human being.

Vision is one of the most complicated senses. How the eyes perceive color is broken down by ocular cells called cones; each allows you to see around 100 shades. Individuals who are color blind, however, have only two types of cones, and are called “dichromatic”.

Each of the three standard color-detecting cones in the retina—blue, green, and red—can pick up about 100 different color gradations, Dr. Jay Neitz, a renowned color vision researcher at the Medical College of Wisconsin, estimated. However, the brain can combine those variations exponentially, he said, so that the average person can distinguish about one million different hues.

Dr. Neitz, who conducts his research with his wife Maureen, said only women have the potential for super color vision. That is because the genes for the pigments in green and red cones lie on the X chromosome, and only women have two X chromosomes, creating the opportunity for one type of red cone to be activated on one X chromosome and the other type of red cone on the other one. In a few cases, women may have two distinct green cones on either X chromosome.

It is unlikely, Dr. Neitz said, that all of the women with four types of color cones will have the potential for superior color vision, because for many, their two red cones will be so close to each other in the wavelengths they detect that they will not see things much differently than a three-color person does. He estimated that 2% to 3% of the world's women may have the kind of fourth cone that lies between the standard red and green cones, which could give them a colossal range.

Finding tetrachromats through genetic screening is one thing; proving they can see tens of millions of additional colors is another. One research group headed by Gabriele Jordan of Newcastle University in Great Britain has identified a true tetrachromat.

Dr. Jordan started by working backward from certain “color blind” boys to their mothers. About 8% of the world's men have color deficiency, which is the term vision researchers prefer to color blindness. Most of them inherit two red or two green cones along with the standard blue cone, making it impossible for them to distinguish between red and green.

Dr. Jordan's team used vision tests to identify more than one hundred schoolboys in the Newcastle area with that kind of color deficiency. She knew that the mothers of those boys would have either two red or two green cones, and she is now in the process of testing those women to see which of them might be “strong tetrachromats”, as she put it.

To single out such women, she came up with a clever test. Each woman looks into an optical device that shows her three tiny discs in rapid succession. Two of the discs are a pure orange wavelength, and the third is a nearly identical mixture of red and green; they are not told which is which.

Dr. Jordan reasoned that women with two distinct red cones would see the red-green disc differently than the orange discs. Of the 20 women she has tested so far, only one was able to instantly and accurately identify the red-green disc each time. She is now conducting genetic tests on the woman's saliva to verify whether she has the genes for distinct red cones.

Based on Dr. Neitz's estimates, there could be 99 million women in the world with true four-color vision. However, before they pat themselves on the back for their superior evolution, he said, it is important to note that humans are just getting back to where birds, amphibians and reptiles have been for eons.

Those creatures have long had four-color vision, but a main difference is that their fourth type of color detector is in the high-frequency ultraviolet range, beyond where humans can see. In fact, that conclusion allowed scientists to figure out recently why the males of some species of birds did not appear to have brighter plumage than the females, Dr. Neitz said.

The problem was in the observers, not the birds, he said. When those species were viewed through ultraviolet detectors, the males had markedly different feathers than the females.

In a similar way, he said, our eyes are not capable of seeing the world the way a true four-color viewer perceives it, and so we have no way of knowing how many advantages that might give to tetrachromats.

There are many things in the world that are physically different from one another that you cannot tell apart now with three-color vision, but a four-color woman presumably would see the distinctions indeed!

*Published in PSC Newsletter2nd School Semester 2012/2013 issue.


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