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How do you see?

How do you see?
Joe Lyons from Swansea (Age 5-14)

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One Response

  1. All of the organs in our body are made up of cells of different types that have different functions. In our eyes we have cells that can receive light called photoreceptors.

    What we see is light that is reflected off everything. White light (which is made up of all the colours) comes from the sun and shines on the things around us. Those things might absorb some parts of the light and reflect the rest. For example, grass is green because all the other colours are absorbed into the grass but it doesn’t use the green light so that is reflected out to be seen.

    So it is light that comes into our eyes and it makes proteins in the photoreceptor cells at the back of our eyes change shape in a way that matches the colour they have received. The changing protein shape leads to a sort of chain reaction in the cell that sends a signal to the brain. The brain knows that this particular signal means there is a certain colour being seen in each single photoreceptor and pieces together all the signals, a bit like a jigsaw puzzle or the pixels on your computer monitor, so that the whole picture can be understood in your brain. That picture is whatever it is you are looking at.

    This happens very very fast of course and all the time so we have continuous vision.

    By having two eyes instead of just one we get slightly different images in each (close one of your eyes and look at something in front of you then without moving your head, close the other eye instead and the thing will appear to have moved a bit to one side). The brain pieces together the images from each eye and uses it to give a 3 dimensional picture so that we can perceive depth, that is how far away things are from us.

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