Figure-Ground illusion

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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)