Thanks Anwar for this nice example of figure-ground shift. There are
many examples around, the most popular one being of the old woman's head
shifting to the young woman's full figure, which can be found in most
any introductory psychology textbook , usually in a chapter on
perception. There is a quite wonderful example that used to be in the
entry to the Museum of Modern Art in New York, of a sort of tree of
life, where hundreds of figures of babies were hidden among the branches
and leaves. (New Yorkers: Is it still there? Haven't visited for a
good while.) The Gestaltists used figure-ground shift as evidence of
cognition, i.e., the role of the organism in organizing perception.