Release Message:  Set of ambiguous or bi-stable (i.e., reversing) two-dimensional forms developed around 1915 by Edgar Rubin.

Description:  Set of ambiguous or bi-stable (i.e., reversing) two-dimensional forms developed around 1915 Rubin explained the illusion as follows: One can then state as a 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.