Rubin vase

Rubin's vase (sometimes known as the Rubin face or the figure–ground vase) is a famous example of ambiguous or bi-stable (i.e., reversing) two-dimensional forms developed around 1915 by the Danish psychologist Edgar Rubin.

The depicted version of Rubin's vase can be seen as the black profiles of two people looking towards each other or as a white vase, but not both.

Another example of a bistable figure Rubin included in his Danish-language, two-volume book was the Maltese cross.

Rubin presented in his doctoral thesis (1915) a detailed description of the visual figure-ground relationship, an outgrowth of the visual perception and memory work in the laboratory of his mentor, Georg Elias Müller. One element of Rubin's research may be summarized in the fundamental principle, "When two fields have a common border, and one is seen as figure and the other as ground, the immediate perceptual experience is characterized by a shaping effect which emerges from the common border of the fields and which operates only on one field or operates more strongly on one than on the other".