The Vision of Johanna. And Jenny. And you and me

The eye on the left appears blue, but in fact it is exactly the same colour as the eye on the right.

Vision and colour are central to our perception of the world. But vision in general, and colour vision in particular, are still in 2011 subtly mysterious. I have been reminded of this several times recently and I just thought I would note three curious things about our vision system which continue to fascinate me.

The first is the variability of colour vision from person to person. At the celebratory drinks after the end of the 14th presentation, Protons for Breakfast graduate and Bob Dylan fan Joanna [pace the title] explained that she had distinctly different colour vision in each eye. The situation was such that at times she simply wasn’t able to say definitely what colour she really thought some things were! My colleague Jenny at NPL has also mentioned this but she seemed less troubled by it. But if I personally know two people with distinctly different colour vision in each eye, then how likely is it that your colour vision is the same as mine? Or that anybody’s colour vision is the same as the ‘standard’ sensitivity curve decided on by the International Commission on Illumination (CIE) in 1931?

  • Test the sensitivity of your colour discrimination here – its tricky!

And then there is the issue of the way we infer colour from context. I took the image at the start of this article from a slide show over at Scientific American. I simply didn’t believe that the two eyes were the same colour. So I downloaded the image, and sure enough in the image on the Scientific American web site, the eyes were slightly different colours. So I edited the image to make them exactly the same – that’s the image at the start of this article – and the illusion is still there. It is very unsettling to realise that our perception of a particular shade as ‘blue’ or ‘grey’ can be quite so context sensitive. In some of the images in the slide show, the author states that the explanation of the illusion is still unknown.

And finally there is the fact that even, after 150 years of careful study, we are still finding out new things about the structure of the eye itself. Scientific American this month reports on some astounding work that has uncovered additional light sensitive cells in the retina of human eye. The work is based on some very simple observations – that blind mice still responded to the daily cycle of light and dark, and still reduced pupil size in a bright light. Following on from this, the author, Ignacio Provencio, and his colleagues, uncovered previously unnoticed cells, comprising around 1% of the normal cone cells which are not part of the normal imaging system. Instead they are linked to the part of the brain which controls our daily cycle – the circadian rhythm – and also controls our pupil size.

So if we understand our visual system so little, how can we be sure that we really understand anything we see? Perhaps, the pattern of tiny pixels on my computer screen do not really indicate that it is now 45 minutes past midnight? Perhaps it is all just an illusion. Somehow, I doubt it. Goodnight.

UPDATED 7:23 a.m. 26th April 2011: Thanks to Nick Day for the comment and the additional links.


4 Responses to “The Vision of Johanna. And Jenny. And you and me”

  1. Joanna Harker Says:

    Thanks for this Michael! Can’t say how much it’s cheered me up this morning!
    I took the colour hue test and scored an utterly abysmal 95 (with 0 being the perfect score), persuading me never to work in the visual arts… although maybe I should, as I’ve heard theories that both Turner and Van Gogh had colour vision discrepancies!

  2. protonsforbreakfast Says:

    Glad it cheered. Thanks for sharing this. And today I learned that my office mate Gavin >also< had different colour vision in each eye. So that's three people I know. I also took the colour acuity test and I got 9, and my children 17 and 27 – so at least I am still good for something! Needless to say Stephanie scored 0 – perfect colour vision.

    I have a couple more things to say about this subject – so stay tuned.

    All the best


  3. More illusion confusion « Protons for Breakfast Blog Says:

    […] Protons for Breakfast Blog Making sense of science « The Vision of Johanna. And Jenny. And you and me […]

  4. Bernard Naylor Says:

    Many years ago, I attended a lecture by a man called Trevor-Roper, an eye specialist, and brother of the more famous historian, Hugh Trevor-Roper. He was putting forward the thesis that some artists’ paintings suggest that actually their view of the world was affected by specific eye defects which today are clinically recognised. I remember him saying that El Greco’s paintings suggested that he suffered from a defect which caused ‘his’ world to have that strange swirling form so familiar to us. He also said – I think I recall – that as Turner grew older, his choice of palette shifted noticeably towards the red, and that this was probably due to a specific deterioration caused by ageing. What he never tackled was why, if Turner’s view of the world was like that, he actually used a red-shifted palette. Surely – I thought – his defect would have carried across into the impact that the colours on a normal artist’s palette would have on him. So why shouldn’t we see his paintings as normal?

    But I never got to put the question, being much less assertive in them days…..

    Kind regards


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