Let’s get this straight from the off. You don’t see nearly as much as you think you do. In fact you barely see anything. You may think this is an exaggeration but I’m being serious. And I’ll explain why.
Before we start you should read the first post in this series.
Firstly you don’t see smooth motions in the world around you. The neurons in your eyes can’t work that fast. They have their own frame/refresh rate at which they have to work, similar to a TV. In fact a TV has a higher frame rate than your eyes do, which is why your TV shows look so smooth.
So why doesn’t normal vision look jerky, and why can’t we see the individual frames (like with an old flash animation, or a strobe light)? It’s the same reason as to why we don’t notice our blind spot. Our brain fills in the gaps. It blurs the frames together to make a smooth motion.
So not only does our brain fill in the blind spot, but it fills in gaps in time between each individual frame of vision. It does this in real time, as we are seeing. It’s essentially the fastest movie editor ever created.
Even so, in my opinion, that is not the most extreme example of the brain filling in gaps. For me what was probably the weirdest thing is the amount of the world you can actually see in one go.
Stretch your arms out to the side until they are right on the edge of the field of your vision. Move your fingers to make sure you can actually see them.
Most people would probably say that’s how much they can see. And it’s true, that is the size of their field of vision. But lets be honest, if someone asked you to read something from that position, you wouldn’t have a hope in hell.
No, instead give the laptop a thumbs up, holding your arm as far in front of you as you can.
The nail on the end of your thumb, at about this distance, is all you can really see in any detail.
There is a small place near the blind spot called the ‘fovea’. It’s directly opposite your pupil and holds about 50% of the neurons in the retina that can see light. That’s a huge amount of neurons in a tiny amount of space, and all it can see is your thumbnail.
Look at the word marked out in bold in this paragraph. Try to see how many words surrounding it that you can read while only looking at the word in bold. Now read the rest of this paragraph. Most likely you could only read words a centimetre or two away from the word in bold. Anything further than that and you could make a guess, but you probably couldn’t read it. Outside of this small area your ability to see becomes drastically worse, and your ability to read is seriously damaged.
That’s because the other 50% of neurons in the retina have to be spread out over a wide area. The more spread out these neurons are, the harder it is to see.
Here’s a couple of pics from wiki to help you understand:
This graph shows how well the fovea see’s in comparison to the rest. The peak is the fovea, with the drops on either side being everything else:
The fact that we can only really see a tiny bit of our visual field isn’t much of a problem, especially when you consider that most of the time we look at what’s directly in front of us. On the other hand we only really pay attention to things in our peripheral vision when something moves, which we only need a few cells to do. In fact there is so little need for detail in peripheral vision that we can’t really see colour outside of the fovea.
If your asking: Why then do I see everything in colour?
My answer is: You don’t, but guess what. Your brain fills the colour in!
We have way more cells in the eye that detect black and white than we do colour. And most of the ones that detect colour are in the fovea, as we need the detail there. However the brain still feels the need to colour the world in for us so that we get a more complete picture.
The way we do this is by constantly moving our eyes around, or ‘foveating’. We do it without realising but it allows the brain to collect bits of information from the whole area. with that information it can colour in the world for us.
Want to test this?
Buy loads of different coloured paper. Or coloured pens, or something that is in loads of different colours.
Get a friend.
Ask them to go behind you with the paper or other coloured items.
They have to choose one at random and hold it just on the edge of your visual field without you seeing it outright.
Guess the colours.
On the edge of your vision you should have trouble guessing which colours they are, especially with objects of a similar colour. Allow them to bring the object closer to you field of vision, slowly, and eventually you will be able to see which colour it is.
Bright and fluorescent colours are much easier to see however, even on the edge of your vision.
What this post and the last have been trying to say is that a huge amount of what we see is actually the brain filling in gaps to make this world look a lot smoother and more continuous. This is just part of the way that the brain interprets the data it receives from the eyes.
And it’s the way the brain interprets this world that leads to optical illusions. Which I’ll explain in the next post.