Interactive effects of explicit emergent structure: a major challenge for cognitive computational modeling.

David Marr's (1982) three-level analysis of computational cognition argues for three distinct levels of cognitive information processing-namely, the computational, representational, and implementational levels. But Marr's levels are-and were meant to be-descriptive, rather than interactive and dynamic. For this reason, we suggest that, had Marr been writing today, he might well have gone even farther in his analysis, including the emergence of structure-in particular, explicit structure at the conceptual level-from lower levels, and the effect of explicit emergent structures on the level (or levels) that gave rise to them. The message is that today's cognitive scientists need not only to understand how emergent structures-in particular, explicit emergent structures at the cognitive level-develop but also to understand how they feed back on the sub-structures from which they emerged.