Each of your eyes receives a different picture from the other. And the brain collects each of the pictures received by the 2 eyes and merges them into single 3 dimension picture which you see.
What happens if you receive only one picture?
Try this: I think you are in front of the computer about 50 cm. Close your right eye and concentrate on the cross mark in the picture below you see it and the black ball.
Now move slowly towards the screen and observe.
You will notice that at about 30 cm the black ball disappears.
Now what happens?
Each eye has a blind spot in the retina (The retina is a thin layer of cells at the back of the eyeball). This blind spot contains no photoreceptors (cells which receive the light).Thus, preventing the complete picture from getting to the brain.
So, Why is the Blind spot ?
This design allows a good blood supply close to the retina to both nourish the photoreceptors and help metabolize debris that accumulates there.
The other eye fill this black spot in most cases and even if the other eye doesn’t provide useful information the brain has mechanisms to fill in the hole. This filling in is why you see the white background.
Thanks god for great creation.
Read more:
http://serendip.brynmawr.edu/bb/blindspot1.html
http://serendip.brynmawr.edu/bb/blindspot2.html
http://www.exploratorium.edu/snacks/cheshire_cat.html
http://en.wikipedia.org/wiki/Blind_spot_(vision)
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