I’m a Tetrachromat – And Other Tales of Bad Science

I have some wonderful news, readers – my amazing skill at being able to see both colours in the dress is down to the fact I’m a tetrachromat – a marketer says so.

Firstly I’ve always known I was special. When everyone else said I had poor colour vision, I just knew I was discerning subtle differences in colours that they couldn’t even perceive. When people said how much they loved spring green, I knew how tasteless they truly were. When nobody believed in me, I would look at the glorious colours that surrounded me and quietly comforted myself in their glory.

A rainbow of colour nuances . . . apparently

 

The LinkedIn article discusses some truly groundbreaking new research. View the above rainbow, seemingly created by Professor Diana Derval who’s an expert in neuromarketing. Crazily enough, she uses something very like Articulate Storyline to build her website – we are clearly bound by fate! Derval asks you to count how many colour nuances you see in this rainbow. I see 36 on this screen, 38 on my phone and 34 on my screen at work. Let’s take an average of 36.

If you see less than 20 colours, Derval suggests you are a dichromat, like dogs, which would be red-green colour blind typically. You would struggle to see the ’57’ in this image.

If you see between 21 and 32 colours, Derval suggests you at trichromat, like . . .well . . . the majority of humans.

If you see between 33 and 39 colors, Derval calls you a tetrachromat. Still not as cool as a mantis shrimp, but apparently you’re more able to see purple (?) and you’ll be irritated by yellow. I’m irritated by spring green tinged yellows, and lemon yellows wash out my skin tone, but a golden yellows are everywhere in my wardrobe because I fricking love yellow.

In her article, Derval points to a paper by Jameson et al (2001) which investigated the genes linked to tetrachromaticity and colour perception in 64 people (38 women and 26 men, all based in California if that influences your thinking any).

First Jameson et al investigate the genetic sequence that’s responsible for the light-sensitive parts inside our eyes. First for a short physics lesson: the rainbow is made up of what we call a spectrum of light, and each colour has its own wavelength. We say humans are trichromats because we have cells in our eyes that can pick up three broad wavelength bands: red, green and blue. Because light is a wave (at least for the purposes of this blog post)  – we can see the rainbow as its the overlapping wavelengths. We can see orange because it sits in the overlap of red and green.

 

The parts of the human genetic code that make all the light sensitive parts of the eyes are complicated. Our genetics hold more possibilities than our eyes actually come out with – which makes figuring out how people see very complicated!

If a human has two different amino acids  (amino acids are basically important things the help the body do its body stuff) coded on a particular gene – there’s a possibility they could be tetrachromat. That is to say that as well as the three light wave frequencies ‘normal’ humans can see, they have another which is sensitive to a fourth.

Of the 64 subjects they had 23 women had these two amino acids on the gene (possibly genetically tetrachromat), 37 people who were trichromats (or ‘normally’ sighted), and 4 men who were dichromat (or red-green colourblind).

After checking the genes, the researchers investigated what these 64 people saw. To do this, they didn’t use a computer screen. Instead they shone a light through a prism, like the old school experiment, and asked the subjects to draw lines demarking where they saw ‘colour partitions’.

What’s different between this methodology and the LinkedIn article? Firstly – no computer screens, or monitors of any type. The subjects were looking at pure light – light scattered through a prism – which is different from a computer attempting to display colours based on RGB numbers (or worse, html). The computer also has to be told what colours to display, there are only 39 colours in Derval’s rainbow (each one a fixed width apart so we ‘know’ where a colour demarkation should be, even if we observe it as a broader band. This is very poor design as well, you could at least randomise colour band width to stop people from assuming they should see a colour difference. For the record, I’m positive this is why I’m scoring so highly because my colour vision really is poor), and so we’re not really choosing what colours we see – not like the subjects were in Jameson’s experiment.

So what were the results? The genetic tetrachromat women (n = 23) saw on average 10 spectral delineations, the 15 trichromat women saw 7.6 on average. This was significantly different at the P<0.01 level, though it’s very important to recognise the small sample sizes and also that the tetrachromat women were very variable (e.g. one tetrachromat woman might see 7, another might see 13). The trichromat people in general (n=37) saw 7.3 delineations on average, and dichromat men (n=4) saw 5.3. This was also significantly different.

Jameson et al concluded these results demonstrated that their rainbow test was a good, non invasive indicator of whether someone is tetrachromat or trichromat. They also suggested that we aren’t very good at detecting tetrachromats with our traditional colour testing, which I more than agree with.

I disagree, strongly, that Derval’s method has any chance of trying to identify who these people are. The methodology is not sufficient. But more than anything else, Derval suggests that tetrachromats are not tricked by the dress. This tells me that not only is a professor of marketing cashing in on a phenomenon to plug her book (and more power to her – I use search engine optimisation to do the exact same thing), but that she doesn’t understand how the Dress illusion works because it has nothing to do with how good your colour vision and everything to do with how your brain is primed to interpret images.

These kind of internet tests are fun – but for heavens’ sakes, don’t trust them! They are as precious as the paper they’re printed on.

 

And I promise I will stop talking about the dress.

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One thought on “I’m a Tetrachromat – And Other Tales of Bad Science

  1. Pingback: FluffySciences in 2016 – fluffysciences

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