How does the human eye percieve colours?
ACE
First, let's take a look inside the eye...
First, let's take a look inside the eye...
Cones and rods are the photoreceptors in the retina of the eye which detect colour. They are simply cells! In bright light, such as daylight, six million cones, concentrated in the middle (or fovea), in each eye are responsible for photopic, colour vision. (Cone cells are cones because they are cone-shaped) There are three types of cones: red, green and blue. Therefore, humans are called tricchromats. However, some studies show that 2 to 3% of the world’s women may have a fourth cone which increases their colour differentiation ability, like most birds, and are called tetrachromats.
Rods, well, detect light in very low light levels, giving us scotopic vision. There are over 120 million of them in each eye and highly concentrated around the edge of the retina. They are more sensitive to dim light compared to cones, which is why humans lose most colour vision when they enter a darkened area. Lubert Stryer of Stanford University explained that rhodopsin was the light-sensitive receptor protein in the disk membranes of rods which allows humans to see the tiny pulse of light in the dark.
Rods, well, detect light in very low light levels, giving us scotopic vision. There are over 120 million of them in each eye and highly concentrated around the edge of the retina. They are more sensitive to dim light compared to cones, which is why humans lose most colour vision when they enter a darkened area. Lubert Stryer of Stanford University explained that rhodopsin was the light-sensitive receptor protein in the disk membranes of rods which allows humans to see the tiny pulse of light in the dark.
Light is the origin of colour. Rods and cones simply detect the light, but the brain works together with the eye which transmits messages to the brain, and allows the brain to identify the colour. Optic nerve fibres are the carriers of these messages. Therefore, we can see that colour is not the inherent quality of an object, but what our brain defines it to be. For example, an apple does not emit red, but it reflects light which is decoded by our brain into red colour.
Here are some interesting discoveries:
- The Himba people, (20,000 to 50,000 people living in northern Namibia) can actually easily distinguish similar shades of green which, normal people can barely differentiate.
- Our eyes can perceive more types of warmer colours than cooler ones. 2/3 of the cones process the longer light wavelengths, which are warmer (reds, oranges and yellows).
- If we wish to detect a faint star at night, we should tilt our eyes slightly to the side of the star where the rods are more dominant, and can detect the star more easily. The cones in the fovea would have a hard time doing so.
Colour blindness
Simply put, colour blindness is the inability to distinguish certain colours. This condition affects more men (8% of males) than women (1%) of females). The thing is, most people with colour deficiency are unaware that perceive colour differently from normal people. The most common form of colour blindness is red/green colour blindness, where some of us get confused by red and green.Greens, oranges, pale reds and browns all appear as the same hue.
It is actually a common hereditary disease, passed on by the X chromosome as a recessive disorder. Fortunately, vision is unaffected; only colour differentiation. There is yet another rare form of colour blindness, where blues and yellows cannot be distinguished. Finally, the most unfortunate form would be the inability to identify any colour, seeing everything as black and white.
It is actually a common hereditary disease, passed on by the X chromosome as a recessive disorder. Fortunately, vision is unaffected; only colour differentiation. There is yet another rare form of colour blindness, where blues and yellows cannot be distinguished. Finally, the most unfortunate form would be the inability to identify any colour, seeing everything as black and white.
Colour blindness results from the malfunctioning of the cone cells. The X chromosome of the parent gene could have triggered colour blindness in the child. Although the parent may not have the disease, the child can have it. It is not just hereditary, but can also be caused by macular degeneration or from side effects of medicines. This condition would cause people who aspire to be pilots or work in some of the fashion/design industries to give up their dreams, as colour differentiation is important in those jobs.
There are tests to identify colour blind people. One most common one is the Ishihara test, where we have to identify the pattern/number on test plates with coloured dot patterns. Those who are colour blind would either see a different image or nothing at all on the plates.
Can it be rectified?
Sadly, there is no cure for colour blindness if it is hereditary. The consolation is- it’s harmless. There are remedies for colour blindness caused by eye disorders or medication. However, there is a system of lens to enhance colour perception. By using a tinted lens in an eye, the brain sees different colours, allowing one to fare much better in Ishihara tests.
One drawback is that someone who is completely colour blind cannot benefit from this. However, another problem surfaces- colour blind people lose colour perception in another area of the spectrum. Hence, we can conclude that colour blindness has no proper cure; and it is best to stay the way we are right now.
There are tests to identify colour blind people. One most common one is the Ishihara test, where we have to identify the pattern/number on test plates with coloured dot patterns. Those who are colour blind would either see a different image or nothing at all on the plates.
Can it be rectified?
Sadly, there is no cure for colour blindness if it is hereditary. The consolation is- it’s harmless. There are remedies for colour blindness caused by eye disorders or medication. However, there is a system of lens to enhance colour perception. By using a tinted lens in an eye, the brain sees different colours, allowing one to fare much better in Ishihara tests.
One drawback is that someone who is completely colour blind cannot benefit from this. However, another problem surfaces- colour blind people lose colour perception in another area of the spectrum. Hence, we can conclude that colour blindness has no proper cure; and it is best to stay the way we are right now.