In a fraction of a second humans are able to comprehend novel images of objects and scenes. Indeed, the human represents the only existence proof that a general shape recognizer is even possible. Geon theory offers an account of this phenomenon characterized by four general assumptions: a) Objects are represented as an arrangement of simple convex or singly concave parts (geons), b) The geons can be distinguished by binary contrasts (differences) in viewpoint invariant properties, such as

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... ht vs. curved, rather than metric properties such as degree of curvature, c) The relations among the geons are explicit, such as PERPENDICULAR-TO or TOP-OF, as part of a structural description, rather than implicit in a coordinate space, and d) A relatively small number of geons is sufficient. Recent research evaluating these assumptions is reviewed.