The illusion tracks back to 1913 when Mario Ponzo demonstrated for the first time that the perception of an element's size depends on the background behind it. Converging lines create the illusion of depth, and our brains deduce that the rectangle that is farther away from us must be larger — while in fact, both rectangles are the same.

Curiously, people from rural and non-Western regions are less susceptible to the illusion, as well as individuals with the larger size of the primary visual cortex — the area in our brain that processes visual information.^[1]