The vision of David Marr.

Marr proposed a computational paradigm for studying the visual system, wherein aspects of vision would be amenable to study with what might be regarded a computational-reductionist approach. First, vision would be cleaved into separable 'computational theories', in which the visual system is characterized in terms of its computational goals and the strategies by which they are carried out. Each such computational theory could then be investigated in increasingly concrete terms, from symbols and measurements, to representations and algorithms, to processes and neural implementations. This paradigm rests on some general expectations of a symbolic information processing system, including his stated principles of explicit naming, modular design, least commitment, and graceful degradation. In retrospect, the computational framework also tacitly rests on additional assumptions about the nature of biological information processing: (1) separability of computational strategies, (2) separability of representations, (3) a pipeline nature of information processing, and that (4) the representations employ primitives of low dimensionality. These assumptions are discussed in this retrospective.