Here’s a cool illustration from Optical Illusions – Planet Perplex.
Our eyes have a weakness – a blind spot, so to speak. The “optic nerve” displaces the light sensitive cells at a certain spot in the back of your eye. Wikipedia summarizes it thus:
The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called “the blind spot” or the “physiological blind spot”. The optic nerve head in a normal human eye carries from 1 to 1.2 million neurons from the eye towards the brain.
Planet Perplex has a neat demonstration of the blind spot (and a lot of other cool stuff):
Let me know in the comments if this works for you!
Find your blind spot
So I just said your eyes are not perfect. Allow me to demonstrate. Look at the image below. Since the squirrel doesn’t trust the all-too-friendly smile of the boy, he wants to get out. Let’s make him disappear ! Close your left eye, then look at the boy (probably with your right eye). Slowly decrease (or increase) the distance to the screen until … the squirrel is gone !
Whoa ! Seems you DO have a blind spot, and it’s large, too ! There is a certain spot in the back of your eye where you can’t see. It’s where the optical nerves (“wiring and cables”) enter the eye.
This is also a brain illusion. Think about this : do you see a huge floating gap everywhere you look ? No ? But you just learned you have a blind spot so … your mind just guesses what should be there and shows it to you !
Your mind “guesses what should be there”, but it also blends the information from both eyes…