Colour #4: Perception

At the end of Through the Language Glass, Guy Deutscher points out that colour, like beauty, lies in the eye of the beholder. As is well known, the eye has rods and cones. Colour perception is because of the cones. In humans, we have 3 different types of cones which can detect 3 separate colours – red, blue and green (RGB). Only those three, nothing else. How then do we “see” so many other colours?

 

Well, if light happens to activate both red and green cones with equal intensity, it gets interpreted as yellow. Put differently, we are not capable of detecting if a light is “truly” yellow or just a combo of equal intensity red and green! So all those non-RGB colours we are able to see? It’s just a combo of those three colours we can detect (RGB) combined in different intensities (ratios).

 

In fact, colour TV’s use just this point. They (like our eye) only support 3 different colours (RGB). By varying the intensities of those three colours at each pixel on the screen, they produce the illusion of multiple colours.

 

Colour blindness is when one (or more) of the cone types don’t work. Depending on which type of cone is not functioning, the individual loses the ability to see certain colours (remember, they don’t just fail to see the one colour corresponding to the cone; they also lose all colours formed by a combo that includes the faulty cone’s colour).

 

Wait, there is more. The brain is not a passive computer that crunches the data coming from the eye. It adds its own, er, inputs to the signals. Why? Because we live in an environment where the background lighting changes (shadows, dawn, bright sunlight, dim, bright etc). Once the brain has associated certain objects with certain colours (over time), it will go out of its way to assign the same colour to that object the next time, and adjusts for background lighting differences. If the brain just took in the signal received, we would perceive an apple (and everything else) as a different colour depending on the lighting. That would be very confusing, hence the evolution of the brain to compensate.

 

Wondering how/if this can be proved? Well, they showed people a yellow coloured square on a computer. They then changed its colour gradually. The task was to press a button when the colour became grey. Say, the individual clicked for grey after X time. Next, they repeated the same steps, except this time the square was replaced with a banana. This time, people took longer than X time to state that the colour had become grey. Why? Because the brain expected the banana to be yellow, so it had turn a lot more grey than before the brain finally “accepted” that its colour had become grey!

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