While there is still some controversy concerning the acceptability of the idea of a serial sequence of processing stages in human information processing as opposed to a holistic, integrated, unified process, few viable alternative theories have been forthcoming to the sequence-of-stages approach. Even those scholars who appreciate some of the problems associated with serial processes (e.g., van de Grind, 1984) and who cite in passing such alternatives as the direct, ecological perception approach of Gibson (1966, 1979), usually revert to a model that is implicitly serial when they become specific about the details of their own cognitive theories. While this may be due to the limits of contemporary theorizing, it is, however, also true that the anatomy and physiology of the nervous system, as we currently understand it, is strongly suggestive of a series of anatomical, if not functional, stages. Whether they deal with “observers” or “primal sketches” and no matter how parallel the mechanism underlying an individual stage may be, some of the most up-to-date models (e.g., Bennett, Hoffman, & Prakash, 1989; Marr, 1982) still consider the visual system to function as a series of processing stages conceptually comparable to the anatomic stages of neural information processing. Observers pass information sequentially to other observers; the primal sketch passes the outputs of its transformation to other, more central, levels for further processing and subsequent transformation into a 2 https://www.w3.org/1998/Math/MathML"> 1 2 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315807065/8cb3f661-d31c-4056-8763-98fc22b2269c/content/inline-math_1_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> D and then 3D representation.