Colour: Visual Perception and Eyes.

Sighted humans, along with other sighted mammals, use vision and colour identification for survival. Though in most modern human societies colour perception isn’t a life or death matter it certainly has been over the centuries.

​Colour Confusion​

The First Battle of Bull Run (also known as First Manassas) is a great demonstration of the importance of colour. During the American Civil War the uniforms of the Union and Confederate armies were quite similar colours, grey, blue and blue-grey.

During the battle one of the Union leaders, Major Barry, mistook a marching troop coming towards his men, as his own side. His failure to identify the Confederate troops meant that what had been looking like a certain bet for the Union side, became a Confederate victory. This was not the only instance in which confused colours caused problems during the American Civil War and later uniforms became increasingly more distinct in colour.

 

 

Eyes

The reason that we, and several other animals, can distinguish between different colours is thanks to rods and cones.

The retina is the part of the eye onto which images are projected. This image is translated by the brain. Rods and cones are cells within the retina which have responsibility for photo reception, i.e. they receive the light projection for the brain to translate.
The cone cells are what help us distinguish colour differences. These are less sensitive, and thus not especially helpful when light is poor.

In humans there is a higher concentration of them at a point on the retina called the fovea. This point is where your daytime vision is most accurate. This is the point where most light should hit your retina.

 The rod cells are better able to cope with poor lighting conditions, but are less able to distinguish between different colours. The differences in these two cell types mean that animals adapted for various environments will have different amounts of either.

For example fish that live in deep marine environments don’t require especially efficient colour vision, but they do need to be able to see well in murky waters so tend to have more rod cells.
 

Colour blindness

 

Of course it’s possible that colour might not have helped Major Barry, had he suffered from colour-blindness. T

his is a genetic condition is most commonly caused by cone cells to failing to develop properly. As a man Major Barry had a reasonable chance of having colour vision problems, as around about 9% of men have colour blindness.

Whilst less than 0.5% of women do.
 

The reason for this is that the genes which code for, i.e. make, the cone cells are located on the X chromosome. Males only have one X chromosome, so if their cone code is faulty then they may suffer from a type of colour blindness. Whereas females have two X chromosomes, so if one code is wrong, the second, functioning gene is there to correct this problem.

The most common type of colour blindness is Anomalous Trichromatic Deuteranomaly, and this is when the person finds that green based colours look more like reds to them. People with this kind of colour blindness may also find that dark greens look black. 
 

Most people with colour blindness have some kind of colour confusion rather than a complete absence of all or any colours. However, there are two types of colour blindness that do cause this.
People with Blue Cone Monochromacy for example see the world as various shades of blue because they lack both red and green cones. They often have generally poor eyesight and may have problems with eye movements.
 Whereas people with Achromatopsia have no cone cells at all. This condition is generally rare, but on the island of Pingelap around 10% of the population see everything in black and white. Artist Neil Harbisson  uses an eyeborg to hear the colours that he cannot naturally see, as he was born with achromatopsia. The cybernetic attachment translates colours into wavelengths, which themselves map to musical notes. Harbisson accordingly has renamed his condition sonochromatopsia, as colours now make a sound for him.



Next Infrared and Ultraviolet​​