Numerical distance effect in developmental dyscalculia

Children in third and fourth grades suffering from developmental dyscalculia (DD) and typically developing children were asked to compare numbers to a standard. In two separate blocks, they were asked to compare a number between 1 and 9 to 5, or a two-digit number between 10 and 99 to 55. In the single-digit comparisons, DD children were comparable to the control group in reaction time but showed a difference in error rates. In the two-digit number comparisons, DD children presented a larger distance effect than the controls. In addition, they were more influenced by the problem size than controls were. Assuming an analog representation of quantities, this suggests that quantities are less differentiated in those with DD than in typically developing children. (C) 2009 Elsevier Inc. All rights reserved.