Tetrachromacy: Do you have superhuman vision?
19 January 2021
A world of 100 million different colours
We’ve all heard of some people being colour blind and how the condition impedes your colour vision, but how many of us have heard of tetrachromacy? This is a condition affecting your colour vision which enables you to see around 100 million shades of colours. To put this into perspective, the average person with standard colour vision sees approximately 1 million different hues, while somebody who is colour blind may see as few as 10,000 colours.
How do we see colour?
The retina is at the back of the eye and is the part responsible for forming images from visual signals. Your retina contains two types of light-detecting cells: rods and cones. There are around 100 million rods in your retina, and between 6 and 7 million cones. Rods detect light and dark, although they cannot distinguish between different colours. Your cones are responsible for colour vision and perceive either red, green or blue shades. Your colour vision relies on all three types of cones working effectively, and colour blindness occurs when one cone colour isn’t functioning properly. A person with fully functioning colour vision has a small degree of overlapping of their cones, but a person with colour blindness has cones which overlap too much, limiting their perception of colour. This means that you may see the colour differently to the way you should, or get it confused with another shade.
What is tetrachromacy?
Tetrachromacy is a condition where a person has four cone types in their retina, rather than the standard three that most people have. It occurs as a result of a genetic mutation and can only occur in women. This is because the gene for our red and green cone types is on the X chromosome (women have two X chromosomes, while men have one X chromosome and one Y chromosome). This means that, very occasionally, women can receive two different versions of the gene, “each encoding for a cone that is sensitive to slightly different parts of the spectrum”. If a man has a genetic mutation on the X chromosome (as he only has one X chromosome) it would result in him being colour blind, rather than tetrachromatic.
How do you know if you’re tetrachromatic?
It is unknown how many tetrachromats there are worldwide. It’s thought that around 12% of women have a fourth cone in their retina, but having an extra cone doesn’t necessarily mean that you have superhuman colour vision. Tetrachromats are so rare that when a new person comes forwards with extraordinary colour vision, it usually makes the news. Concetta Antico, an Australian artist, realised she was tetrachromatic when one of her former art students sent her an article about studies into tetrachromacy. Antico had always told her students she could see colours in their work or in their surroundings on field trips, which they couldn’t identify. She believed that she simply could see more as a trained artist, and didn’t realise it was because of a genetic mutation giving her a fourth cone and revealing 100 times more colours to her! She underwent genetic analysis in 2012 which confirmed the presence of a fourth cone.
There are different tests to establish whether someone is tetrachromatic, one of which involves creating coloured discs with different combinations of pigment in them. Using one base colour, the researcher adds a small amount of pigment which most people would not be able to detect. However, true tetrachromats can quickly identify which colour has been added to each disc (e.g. noting that one has more red tones, while another has hints of blue), while a person with three retinal cones would see no difference at all.
Another test to determine whether or not someone is a tetrachromat is to ask them to arrange 10 seemingly identical colours in order of how closely the hues match. Again, somebody with standard colour vision would see no difference between any of the colours, so minimal is the variation. This test is then repeated, and true tetrachromats should then arrange the 10 colours in exactly the same order the second time around as the first time.
What is it like to be tetrachromatic?
Simply put by artist Concetta Antico, “I see colours in other colours... other people might just see white light, but I see orange and yellow and pink and green... so white is not white; white is all varieties of white”. She likens the condition to a “more intense” version of seeing all the colours on a paint chart which, at times, can be quite overwhelming. Places which have lots of colours close together, such as supermarkets or clothes shops, can also be rather intense environments for tetrachromats.
There’s no denying, however, that tetrachromacy is particularly beneficial for Antico’s work as an artist. She believes that her colour recognition has improved due to the fact she relies on it on a daily basis, and has been able to hone her abilities through painting. Her pieces of art might provide an indication of the range of shades which she and other tetrachromats see, where most of us see just a block of colour.
Antico also notes that she can detect when someone is ill due to the colour of their skin, and also noticed when her baby daughter was jaundiced due to a yellow tinge to her skin, even before doctors had realised she was suffering with it!
Tetrachromacy truly is a fascinating condition and more research is being conducted on it all the time. The more we can find out about the colour vision of people with a fourth cone in their retina, the more we will discover about vision altogether. If you’ve ever noticed that you can differentiate easily between different shades, or are always seeing colours within other colours, you might well be a tetrachromat!
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