Multistable perception

Figure 6.26: (a) The Necker cube, studied in 1832 by Swiss crystallographer Louis Albert Necker. (b) The rabbit duck illusion, from the 23 October 1892 issue of Fliegende Blätter.

In some cases, our perceptual system may alternate between two or more conclusions. This is called multistable perception, for which the special case of two conclusions is called bistable perception. Figure 6.26(a) shows two well-known examples. For the Necker cube, it is ambiguous which cube face that is parallel to the viewing plane is in the foreground. It is possible to switch between both interpretations, resulting in bistable perception. Figure 6.26(b) shows another example, in which people may see a rabbit or a duck at various times. Another well-known example is called the spinning dancer illusion by Nobuyuki Kayahara. In that case, the silhouette of a rotating dancer is shown and it is possible to interpret the motion as clockwise or counterclockwise.