Profound developmental dyscalculia: evidence for a cardinal/ordinal skills acquisition device.

This article presents an analysis of a form of dysfunctional mathematical development. A child of normal intelligence was unable to acquire basic cardinal numerical skills, despite relatively intact ordinal number use. These findings provide evidence for an innate "cardinal/ordinal skills acquisition device" (COSAD). It is argued that if this COSAD is lacking, ordinal number use may be compensated for by linguistic logic and visual skills. Cardinal number skills, however, remain limited as these demand an innate internal representation of quantity, which cannot be compensated for. The findings are discussed in terms of different approaches to number development. Copyright 1997 Academic Press.