Tetrachromates

27 June, 2006

While ferreting around on the previous post I found reference to the fact that some women may actually be tetrachromates, seeing four basic colours rather than 3 for normal people or two and a bit like me.

There doesn’t seem to be an awful lot published on the issue, a few papers like this one but not a vast literature from what I can find.

The idea is interesting. There is even the suggestion that it could be expressed in the mothers of colour blind boys, which would have an impact I imagine about whether colourblindness genes were a net negative or positive selection criteria.

For years now, scientists have known that some fraction of women have four different cone photopigments in their retinas. The question still remains, however, whether any of these females have the neural circuitry that enables them to enjoy a different — surely richer — visual experience than the common run of humanity sees. “If we could identify these tetrachromats, it would speak directly to the ability of the brain to organize itself to take advantage of novel stimuli,” says Dr. Neitz. “It would make us a lot more optimistic about doing a gene therapy for color blindness.”
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Colour blindness again

27 June, 2006

Interestingly, my previous post about my colour blindness seems to be getting me the most search hits. Hopefully it has helped direct people to some of the things they are interested in. If not here are some other places to look.

For those of you who are interested in reading about this, don’t miss Colorblindor a blog mostly about the experience of being colourblind. This post also discusses the experience.

This blog has a post about the troubles someone in practice may have reading the website (ie. not many but some).

This site has some facts and a short self test, plus some links, as does this one and this one.

Update: Some scientific papers on colour blindness.

  • Defective Colour Vision and its Inheritance (scanned pdf)
  • Impact of congenital colour vision deficiency on education and unintentional injuries: findings from the 1958 British birth cohort which has some responses
  • Colour vision deficiency in the medical profession. (pdf)
  • New aspects of an old theme: the genetic basis of human color vision. (pdf)
  • Doctors and the assessment of clinical photographs–does colour blindness matter? (pdf)

  • Colour Blindness

    12 June, 2006

    I am colour blind. As was my brother, both my mother’s brothers, and my great grandmother. It runs in the family. More specifically I am red-green colour blind, and even more specifically appear to be suffering from Protanopia, an absence or at least weakening of the red portion of the spectrum. Most colour blindness, particularly red-green colour blindness is due to a recessive genetic condition on the X chromosome. Men, with only the short Y chromosome, have no way of masking the recessive gene and so are much more likely to express the condition. Colour blindness in some form is quite common. Around 8% of the male population in Australia has some form of colourblindness with Red-Green being far and away the most common, although some may have it mildly enough not to realise it until made do a screening test. Colour blindness was first described scientifically in 1794 by the chemist John Dalton who diagnosed himself and published the paper Extraordinary facts relating to the vision of colours. For a long time afterwards colour blindness was known as Daltonism.

    When I tell people I’m colour blind, you usually get the same set of questions. What colour is the grass, the sky etc. These questions are annoying but I guess understandable. My answer always is that the sky is blue and the grass is green and that these are basically definitional to most peoples conception of colour. The issue with colour blindness is distinguishing between colours, in my case any colour involving red. Thus green, brown and red can all look very much the same, particularly when there is either not strong light, or there is only a small amount of the colour.
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