The picture I’ve put up is one of a mouse retina. The green dots are cells that have been stained with a fluorescent dye. I’m showing you this partly to show you how many cells there are in a retina (only some of the cells are stained, and humans have even more than mice). It’s also partly to complain about how I’ve been given the honourable job of having to COUNT every single one.
Anyway this is a continuation from the previous post. I finished off by talking about how we transfer what we see from the eye to the brain. Now I want to talk a little bit about what the brain sees.
The honest answer is a lot.
When you get to the brain you find cells that don’t just see a small point in space, you find cells that see different colours in that space, cells that see things pointing in specific directions and some cells that see things moving in specific directions. That is probably a very basic breakdown of the different types of things you see when separated into broad categories.
I’m going to make a small mention about the direction type cells in one of my next posts as you can do some weird things with them. But for now I’m going to concentrate on the colour ones as it might be a bit more relateable!
These are the three scientific primary colours, Blue, Green and Red. You might know them from TV input cables called ‘RGB’. For some reason artists consider the three primary colours to be blue, yellow and red. I don’t know why, can someone please tell me why?
So why are scientists right? It’s simply because we have only three types of cells that detect colour. One detects red, one detects green and one detects blue. These cells are represented by the white lines in the picture above. Together they are known as cone cells. Mix those three colours together and you get all of the colours you could ever imagine. See here for more thoughts on this.
It is more or less the same throughout the visual system. You have a group of cells that are specific for certain things (e.g. certain directions) and what you actually see is a mix of these working together. For example if you had a cell that only saw stuff moving left, and one that saw stuff moving upwards. If both of them were active you would assume you would assume you were seeing something moving diagonally. But if you looked at a specific cell you would realise they are really limited.
In fact some people are much more limited than others. In fact we are pretty limited in general. These are generally all of the colours that most humans can see:
However many humans can’t see all of those and are in fact partly colour blind. So below is what a dog can see (famous for being colour blind). It’s one for dogs as the picture was easier to find, no insult intended!:
The reasons why dogs can’t see as many colours is because they only have two cells that see different colours. It can be the same case in humans, but more commonly it is because they have two cells that see colours very close to each other. Imagine M and L lines in the picture above to be much closer to each other. There would barely be a difference!
There are also some people who have ‘monochromatic colour blindness’. This means that they can only ever see one colour. Imagine a world that is perpetually coloured in shades of red. It would probably look a bit like the film Sin City. But that is what they are stuck with.
On the other end of the spectrum there are animals such as the one below that can see in over 12 different primary colours. Imagine how vibrant that must be!
The concluding point of this post is that we have huge amounts of cells in our retina. By the time these cells reach the brain, they aren’t just seeing spots of light, they are analysing the colour of things, the direction they are moving in and even their orientation. It’s a huge amount of information to take in. So one of the next posts is going to be dedicated to how the brain copes with this amount of information, giving us things like optical illusions.