The blind spot test
Close your left eye or cover it with your hand. Stare at the cross with your right eye, never looking away from it, then slowly move your face toward the screen, or away from it.
The experiment starts as soon as the page has loaded (JavaScript is required).
Try the experiment: your result will appear here, next to what most people do.
What just happened (read it after the experiment)
What most people do: For almost everyone, the dot disappears about a foot from the screen, depending on its size.
Where the optic nerve leaves the eye, the retina has no light sensors at all: this is the blind spot, about a millimeter and a half wide. When the image of the black dot falls on it, the dot no longer exists for you.
Why do you never see this hole? Because your brain constantly fills it in with whatever surrounds it. It doesn’t show you the world: it shows you its best guess about the world.
Edme Mariotte discovered it around 1660. He is said to have amused King Charles II of England by teaching him to make his courtiers’ heads “disappear.”
More experiments
Sources
- Edme Mariotte, Nouvelle découverte touchant la veüe, 1668.