Figure–ground perception An object (a figure) is always seen in relation to what surrounds it (a ground, or background). When two fields have a common border, our visual system will interpret the image as two different perceptions, A figure is what we look at and a ground is everything else that forms the background. Generally when you see one of the perceptions, the other region forms a background and is not seen. To see both percepts requires switching back and forth.
Ambiguous figure-ground perception (Figure-Ground Illusion) Figure-ground perception can be ambiguous. The best-known example of an ambiguous figure-ground display is Rubin’s vase-faces stimulus; an adaptation of the original image is shown in Figure on the right. In this display, viewers can perceive either the central white region or the surrounding black region as the figure at any moment. When the white region appears to be the figure, it has a definite shape, one that resembles a white vase or a goblet. The factors that favor seeing the white region as figure include partial symmetry, small area, closure, and enclosure. When the outer black regions appear to be the figures, they have definite shapes, ones that resemble two profiles of people facing each other. The factor of familiarity favors perceiving the black regions as figures. (Global symmetry of the black regions my also play a role.) - (Scholarpedia)
Rubin vase-face illusion
A famous optical illusion image devised by the Danish psychologist Edgar Rubin is often used to illustrate the concept of figure ground. You can see the image as either a central vase, or two faces that are looking at each other.
The “figure-ground” illusion is commonly experienced when one gazes at the illustration of a white vase, the outline of which is created by two black profiles ( see Figure 1: Rubin's vase). At any moment, one will be able to see either the white vase (in the centre area) as “figure” or the black profiles on each side (in which case the white is seen as "background").
Face vs vase
Two face vase
Vase or face?
Variant images of Rubin face-vase illusion
vase face variant
Ambiguous figure-ground illusion
Ambiguous images or reversible figures are optical illusion images which exploit graphical similarities and other properties of visual system interpretation between two or more distinct image forms. These are famous for inducing the phenomenon of multistable perception. Multistable perception is the occurrence of an image being able to provide multiple, although stable, perceptions. Classic examples of this are the rabbit/duck and the Rubin vase. Ambiguous images are important to the field of psychology because they are often research tools used in experiments.(Wikipedia: Ambiguous image)