Numerosity discrimination in children with Down syndrome

To understand the difficulties in mathematics exhibited by children with Down syndrome (DS), this study evaluated the core knowledge of numerosities with a discrimination task adapted from Xu and Spelke (2000). Although continuous variables varying with numerosity were controlled, children with DS discriminated the numerosity 8 from 16, but not from 12. Moreover, their performance did not differ from typically developing children matched either on chronological or mental age. Thus, the approximate numerosity system that recruits parietal lobes (Dehaene, Spelke, Pinel, Stanescu, & Tsivkin, 1999) is efficient in children with DS. These findings point at language-based systems as the source of their difficulties.