Before I start I’m going to give you a couple of references to some relevant posts I have already made/reblogged:
The causes of sensation – very relevant to this post
If anyone still wants to they can vote in the poll on the sidebar!
OK let’s get started.
Vision is complicated. Not because it’s really sciencey and there are lots of long words that you have to learn. (There are some long words, like retinal ganglion cell, but they are pretty understandable when explained). It’s complicated just because it is a very extreme sense and a lot is happening to make it work.
It also happens to be what I’m studying right now, so I might be a little biased!
So starting with the first recommended post: transduction.
Inside the eye there is a layer of cells that detect light, this layer is called the retina. Light hits a cell in the retina (a retinal ganglion cell). This cell has a special chemical (called rhodopsin) inside of it that breaks down when hit by light and causes a chemical reaction. This reaction produces electricity and thus we have that special transduction of light energy into electrical energy.
Brilliant so we have succeeded in allowing light to enter the brain in an electrical form. What is the next bit? Well that’s to do with the last post: Maps (explained using the skin).
We see the world much in the same way that we see a computer screen. If you look really closely at a computer screen, you will probably see all the little pixels that make up the screen. In the same way, if you looked really closely at a retina, you’d see the individual cells. These cells are like our pixels, except there are so many of them that it all looks like one solid picture.
However it has been proven that our eyes are so sensitive that if you were to fire a single ray of light at one single cell in the eye, we would still be able to see it.
The problem with us having so many cells (millions) that detect light and make up the picture that we see (which is essentially a map of the visual world), is that we have to keep them in order.
Imagine having a massive and immaculately detailed puzzle. You come across it already made for you. If you want to move it somewhere else (like we move our interpretation of light from the eye to the brain), you would want to keep it in the same place. It might be easier to just scramble it up and pack it up, but when you want to make it again, it would be a lot of hard work. The brain avoids this by keeping the map together all the way until it gets to the visual cortex in the brain (where we start to interpret what we see).
So light enters the eye. It hits Rhodopsin which is inside a Retinal Ganglion Cell, which is in the retina. Rhodopsin breaks down and causes electricity to be produced. This electricity is carried off to the visual cortex. As there are millions of these retinal ganglion cells we have to make sure everything stays in the same order. This way we can have a reliable picture (or map) of what we see in the brain.
I’m going to stop the post here for now. It might not be really long, but it will get a lot longer if I keep on going. Instead I’m going to carry this over a few posts. So the next post is going to be about some of the weirder goings on in the visual system, how we perceive colour, and why we pay more attention to moving things than things standing still.
If all goes to plan the post after should be about the even weirder stuff like optical illusions and blind spots!