Optical illusion - Hermann grid (1870) - geometric contrast illusion graphics by Benjamin Zierock 

Optical illusions make you doubt your own senses.
However, we often no longer really notice many of the optical illusions that we encounter in nature.
The best-known deception pictures include geometric graphics in black and white, such as the Hermann grid, named after the physiologist Ludimar Hermann.
Ludimar Hermann was one of the first to mention this graphic in 1870. When looking at a white grid on a black background, a washed-out spot appears on every white intersection, only not in the middle of the field of view. Researchers call this a contrast illusion because the contrast between black and white is not captured correctly.