In the previous chapter, I specified perceptual organization as an autonomous process that enables us to perceive scenes as structured wholes consisting of objects arranged in space. Because any scene can be interpreted in numerous ways, it is amazing not only that the visual system usually has a clear preference for only one interpretation, but also that this interpretation usually is sufficiently veridical to guide us through the world. Indeed, it is true that visual illusions show that what we see is not always what we look at, but a fair degree of veridicality seems necessary — otherwise, our visual system would probably not have survived during evolution. In this chapter, expanding on van der Helm (2000), I assess what degree of veridicality vision might achieve by aiming at simplicity. To this end, I elaborate on three related issues, which I next introduce briefly.

Simplicity versus likelihood. The main issue is whether the perceptual organization process is guided by the likelihood principle (von Helmholtz, 1909/1962) or by the simplicity principle (Hochberg & McAlister, 1953). Both principles take this process as a form of unconscious inference yielding interpretations which persons subjectively believe are most likely to be true. The question, however, is what drives this unconscious inference, and as I indicate next, the two principles differ fundamentally in this respect.

The likelihood principle, on the one hand, aims explicitly at a high degree of veridicality in the external world.