Necker Cube, 2012, colour pencil on paper, 30 x 21 cm
There are well-known figures which flip between a few possibilities. These are known as ‘ambiguous figures’. They are extremely important for showing the dynamics of perception, the searching for hypotheses of objects that might or might not be in the external world. Here the answer- the perception- is never decided. There are different kinds of flipping ambiguities- between shapes, depths, and different objects. The best known is the Necker Cube.
Here there is no evidence to indicate which of the large faces is the front or the black. Vision entertains alternative, roughly equally likely hypotheses. So here we see it flip between two equally likely cubes as different depth hypotheses are entertained. What is not clear, is why it is only these depth hypotheses that are entertained and seen.
(Gregory, Richard L, Eye and Brain The Psychology of Seeing, Fifth Ed. 1998)