• Question: how does the brain perceive colour !!!!

    Asked by weekeenan to Anne, Carolyn, Joe, Mariana, Nick on 25 Mar 2010 in Categories: .
    • Photo: Joseph Devlin

      Joseph Devlin answered on 25 Mar 2010:

      Hi weekeenan,

      Tough question because we only know part of the answer. In the retina in your eyes are cells called cone receptors that respond differently to different wavelengths of light. They send their signals to a brain region called the lateral geniculate nucleus (gesundheit!) via the parvocellular visual pathway. (Having fun yet?) These then reach visual cortex in the back of your brain where the visual signals start to be interpreted. In visual cortex is an area called – creatively enough – V4 (the fourth visual area — you couldn’t make this up!). V4 seems to be fairly important for seeing and recognizing colors.

      People with synaethesia see colors associated with everyday worlds (like fire might be green and the number 7 a kind of mauve, etc). These are a fascinating group of people because to them it is entirely normal but there is some evidence to think that they have additional brain connections linking area V4 to other parts of the brain more directly involved in language. My wife is a synaesthete so I get to hear what it’s really like. Makes me wish I was too!

    • Photo: Carolyn McGettigan

      Carolyn McGettigan answered on 25 Mar 2010:

      Well, there are three types of cone cells in the retina at the back of the eye that are preferentially sensitive to certain wavelengths of light. The wavelength of light is the time it takes for the wave to make one whole cycle and return to its original starting point. The S-cones are sensitive to short wavelengths (400-500nanometres), the M-cones to medium (450-630nanometres), and the L-cones to longer wavelengths (500-700nanometres). The colour of reflected light from a given object in the world will activate these three types of cone cells to different degrees, and it is this ratio of activation which is worked out in our visual cortex as combinations of blue (S-cones), green (M-cones) and yellow-red (L-cones) light that we perceive as different colours and hues. Apparently the human brain can detect millions of different hues.

      There are some interesting cultural biases, which show that colour perception happens largely in the brain rather than in the eye and is shaped by experience. So, the words green and blue refer to different colours in English, whereas in Japanese these are thought of as different shades of the same colour.

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