ABSTRACT
The interpretation of two-dimensional retinal images in terms of a threedimensional world is a fundamental problem of vision, which, through evolution and experience, has shaped the neural processing mechanisms in our visual system. An example is the tendency to perceive contrast borders as part of one of the adjacent regions, as if they were contours of objects in three-dimensional space. Rubin’s famous vase figure demonstrates this compulsion of the visual system (Fig. 8.1). The borders are perceived either as the contours of a vase or as the contours of two faces. Each border is perceived as belonging to one or the other side but rarely to both. In the case of a simple figure, such as the light square of Fig. 8.2A, the contrast borders are of course perceived as the contours of the square; they seem to belong to the enclosed light-textured region. The surrounding gray does not own the borders; therefore, it is perceived as extending behind the square, and hence is called the background. This tendency of perception was first described by the Gestalt psychologists (Koffka, 1935) and was termed the law of the interior (Metzger, 1953).
