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.
- See Beau Lotto’s site for more contextual visual illusions
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.
Tags: Colour Vision