Blind Spot

Instructions: Close your left eye and fixate your right eye on the cross in the first diagram. If your eye is about 12 inches (30 cm) away from the monitor, you should notice that the round dot disappears. This distance may vary according to the screen resolution you have set.

You may be surprised to see that the dot is replaced, not by a black region, but rather blank white space. The brain simply "fills in" the most probable stimulus (in this case, a uniform white area) where there is none.

The following example demonstrates the "filling-in" phenomenon in greater detail. Apply the same instructions as given above and you should notice the red markings each time are replaced by the most probable pattern that your brain is able to perceive.