Optimization and simplicity: Computational vision and biological explanation

David Marr's theory of vision has been a rich source of inspiration, fascination and confusion. I will suggest that some of this confusion can be traced to discrepancies between the way Marr developed his theory in practice and the way he suggested such a theory ought to be developed in his explicit metatheoretical remarks. I will address claims that Marr's theory may be seen as an optimizing theory, along with the attendant suggestion that optimizing assumptions may be inappropriate for cognitive mechanisms just as anti-adaptationists have argued they are inappropriate for other physiological mechanisms. I will discuss the nature of optimizing assumptions and theories. Considering various difficulties in identifying and assessing optimizing assumptions, I will suggest that Marr's theory is not purely an optimizing theory and that reaction to Marr on this issue prompts interesting considerations for the development of inter-disciplinary constraints in the cognitive and brain sciences.Thanks are due to Ron McClamrock for his comments on previous drafts of this material. Also, early versions of some of the material in this paper were presented at LMPS '91 and at a Cognitive Studies Colloquium at Penn State University in 1992. Thanks to those in attendance, especially to Rich Carlson and Mark Detweiler, for their comments. Thanks, too, to an anonymous referee for suggesting several useful references.