Cognitive Development 24 (2009) 387–400 Contents lists available at ScienceDirect Cognitive Development Numerical distance effect in developmental dyscalculia Sarit Ashkenazi ∗ , Nitza Mark-Zigdon, Avishai Henik Department of Psychology and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel article info Keywords: Distance effect Magnitude Two-digit number comparison Developmental dyscalculia Development abstract 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 prob- lem 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. © 2009 Elsevier Inc. All rights reserved. In the case of single-digit comparisons, the larger the numerical difference between two digits, the shorter the time required to decide which is larger, as first reported by Moyer and Landauer (1967). For example, it takes longer to decide that 8 is larger than 6 than to decide that 8 is larger than 1. This distance effect has since been reported in numerous studies (Banks, Mermelstein, & Yu, 1982; Dehaene, 1989; Dehaene, Dupoux, & Mehler, 1990; Duncan & McFarland, 1980; Henik & Tzelgov, 1982; Link, 1990; Moyer, 1973; Moyer & Bayer, 1976; Parkman, 1971; Schwarz & Heinze, 1998; Tzelgov, Meyer, & Henik, 1992). Moyer and Landauer (1967) suggested that people convert written or auditory numbers into analog magnitudes. The digits (representing external magnitude) automatically arouse an internal array of magnitudes, which has become known as the “mental num- ber line” (Dehaene, 1992). The comparison between these magnitudes is made in much the same way that comparisons are made between physical stimuli such as lengths of lines. It has been postulated that the source of the distance effect is the overlap between representations of numbers on the mental number line. ∗ Corresponding author. Tel.: +972 8 6477209; fax: +972 8 6472072. E-mail address: ashkenas@bgu.ac.il (S. Ashkenazi). 0885-2014/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.cogdev.2009.09.006