positive and negative space

Rubin’s vase (sometimes known as the Rubin face or the figure–ground vase) is a famous set of cognitive optical illusions developed around 1915 by the Danish psychologist Edgar Rubin. They were first introduced at large in Rubin’s two-volume work, the Danish-languageSynsoplevede Figurer (“Visual Figures”), which was very well received; Rubin included a number of examples, like a Maltese cross figure in black and white, but the one that became the most famous was his vase example, perhaps because the Maltese cross one could also be easily interpreted as a black and white beachball.