Marr: an appreciation.

The following is based largely on sections of our two recent books: Frisby and Stone (2010, Seeing MIT Press), and Stone (2012, Vision and Brain MIT Press). Those books are aimed at student/ novice audiences, and so we have eliminated material of a wholly introductory nature for this special issue of Perception. However, various debates we have had at vision conferences recently suggest to us that going over basic material on Marr could be useful to many current vision researchers who have had little contact with his work, so we have left in some content of that kind.