In visual perception, data reduction takes place in two respects: establishment of true parts and assignment of features and feature values, which are treated in Chapter 2. The assignment of parts has variously been called organizing, parsing, chunking (Miller, 1956), categorizing (Rosch, 1973b), and schematizing (Bartlett, 1932; Neisser, 1976; Norman & Bobrow, 1976). Wertheimer (1923) thought of the assignment of parts as structuring and considered features as gestalt qualities. His studies were extended by his students, notably Gottschaldt (1926, 1929), Temus (1926), Kopferman (1930), Goldmeier (193611972), and Metzger. Some of their results are described by Kolers (1968a) and Rock (1975). The most comprehensive and authoritative account is Metzger's Gesetze des Sehens (1975), which unfortunately is to date not available in English.