Abstract

The interface between the approximate system and the exact system of quantity processing was examine in 30 children with typical development of arithmetical skills (TD) and 24 children with Developmental Dyscalculia (DD). Both groups were assessing with a non-calibrated estimation task in which the children were asked to estimate the numerosity of dot sets presented briefly. Subsequently, they were evaluating with a calibrated estimation task in which an inductor was systematically presented at the beginning of each block of the stimuli. The inductor consisted in an Arabic number (30.) presented simultaneously with the corresponding set of dots. There were not significant differences between TD and DD children in the non-calibrated task. Both groups showed a tendency to subestimate the numerosities and the property of scalar variability was also observed in the estimation responses in both groups. However, the TD group exhibited more adjusted estimations in the calibrated task respect to the non-calibrated task. Consequently, in the TD group the Weber Fraction -a measure of acuity of mental representation of quantities- improved significantly in the calibrated task respect to non-calibrated task. These effects were not systematically found in the DD group. We conclude that the estimation processing in the typical and atypical development follows the same principles and laws than the estimation in the adult. Therefore, in the DD the approximate system of quantities processing seems to be preserved but a failure occurs in the interface between both systems (approximated and verbal).