How do we perceive colours?

Everyone perceives colours in a slightly different way. We are able to see colours thanks to two particular features of our organisms. First one are the cone cells, which are photoreceptors located in the cornea sensitive. They react differently to different colours. The second feature necessary for colour perception is the extraordinary adaptation of our brains to process the stimuli generated by the cone cells. Electrical impulses, which originate in the cones, reach the occipital visual cortex via the optic nerve. This is where the raw data is processed into colourful, three-dimensional picture.

It takes approximately 0,135 seconds before we are able to tell a colour apart. The specific colour we see is an effect of direct activation of specific group of cones – which are sensitive to blue, red or green light. There are highly specialised proteins which surround light-absorbing particles inside each cell. Shape of the protein determines the specific wavelengths that particular cell is sensitive to. When a photon of appropriate wavelength reaches the cone, the photosensitive particles generate an electric impulse which is then transmitted to the brain. Approximately 25% of the brain is involved in processing the visual input provided by the eyes. Interestingly, given colour as black when no cone cells are activated, while for it to be seen as white all three types of cones are equally stimulated.

Do you know that, despite the fact that everything seems greyish then, we can also perceive colours in half-light? The cone cells are useless in such conditions – they are not sensitive enough to be stimulated by light of low intensity. In such case rods, the second type of retinal cells, become responsible for most of what we see. They are most sensitive to green and blue light and those are the only colours which do not seem grey in half-light.
The perception of colours changes with age. The passing time has its toll on the lens – it thickens and becomes somewhat yellowish. This results in impaired perception of colours such as blue, violet and green. Blue and yellow typically seem darker than they really are and it becomes very hard to discern between hues of blue and violet.
 

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