Apart from seeing the missing sections of these 4 dark disks as the sides of the square (some will even perceive the square as brighter than its surroundings), as well as perceiving the vague contour lines of a square that doesn’t actually exist, this picture holds another great optical illusion. When the brain sees an image like this, it interprets depth relationships to perceive the square as set on top of black disks – as a result, the inside of the square is perceived as being closer to your eyes than its surroundings, ultimately creating visual illusion that makes you think the area within the square is enlarged! How about that? This non-existent square becomes a magnifier magnifying the text behind it. This specially works for spacings above and below each word inside the rect. See it? More similar interactive examples can be found in this Mind Lab presentation. Enjoy!