Saturday, March 11, 2006

Marcus on cognitive descent with modification   posted by agnostic @ 3/11/2006 09:24:00 AM

On a note related to the "math on the brain" post, Gary Marcus will have a new paper out in Cognition (pdf here), in which he puts forward a "descent with modification" (DwM) view of mental modularity. The gist is that we know from double dissociations (where one system is impaired but not some other, and vice versa) that there must be some degree of modularity. However, we also know that other diseases can affect several systems at once, and psychometrics shows that individuals who excel or struggle in one area usually so in others also, so to some extent the diverse modules must share some of their architecture at the neural and/or genetic level as well. He contrasts this DwM view, where mental systems can be variations on a common source, with the conventional sui generis view, where the systems are too unique to spring from a common source. Furthermore, if two mental systems were variations on a common theme, it would require fewer genes to build them and less time for natural selection to design them, vs. having to build the two systems largely de novo.

He discusses the example of language, "the canonical putative module." Though distinct from other systems and a more recent adaptation, it seems to have modified pre-existing features from the following other human systems: memory, spatial & temporal representation, and our more general "who did what to whom" hierarchical encoding of relationships. Perhaps this is how to best interpret Chomsky, Fitch, and Hauser's universally perplexing (pdf) concepts of the Broad and Narrow faculties of language, FLB and FLN -- that is, FLB includes the common sources from which FLN has devised novel variations (FLN also includes de novo inventions).

Marcus is the author of The Birth of the Mind, which examines how we get from genes to brains, and The Algebraic Mind, which is not about math but about the debate in cognitive science over rule-governed symbol manipulation vs. statistics-driven parallel distributed processing. He also co-authored a recent review of the genetics and evolution of human language (pdf here, ctrl F "eloquent").