Procedural Dyscalculia and Number Fact Dyscalculia: Double Dissociation in Developmental Dyscalculia

Abstract

Traditional developmental models describe a series of sequenced stages and interpret developmental disorders in terms of arrested development. Two different cases of developmental dyscalculia are described which cannot both be explained against the same stage model of the development of arithmetical skill. In both cases accurate number processing skills have developed. SW has also acquired accurate number facts and tables but has selective difficulty with the procedures of calculation. HM shows the reverse pattern with normal mastery of calculation procedures but selective difficulty in the mastery of arithmetical tables. The arithmetical modules involved in tables and procedures develop in a semi-independent fashion, neither being an essential precursor of the other. This study demonstrates that there are individual differences in the developmental dyscalculias consistent with individual differences in the developmental pathways to the adult calculation system. It also-demonstrates that the developmental dyscalculias are anala-gous to the acquired dyscalculias.