Abstract
The paper is focused on the current status of knowledge about disorders of mathematical skills and introduces the fi ndings of the study titled "Accuracy and speed in numerosity at individuals with dyscalculia." The main goal is to describe possible causes of these diffi culties. The research compared the performances of individuals with dyscalculia and control participants on a range of number and numerosity processing tasks.
Defi cits in the processing of symbolic numbers and nonsymbolic numerosities, especially in the speed of processing, were observed in the group of dyscalculic participants. We concluded that dyscalculia is related to specific disabilities in basic numerical and numerosity processing which affects the ability to acquire simple counting and arithmetical skills.