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A definition of developmental dyscalculia, stressing the hereditary or congenital affection of the brain substrate of mathematical functions, is put forth. This disorder is clearly distinguished from other forms of disturbed mathematical abilities. A classification of developmental dyscalculia is then outlined, distinguishing the following forms: verbal, practognostic, lexical, graphical, ideognostical and operational developmental dyscalculia. Finally an investigation is presented of mathematical abilities and disabilities in eleven-year-old pupils from normal schools in Bratislava, Czechoslovakia. A number of tests measuring symbolic functions were applied to 66 suspected dyscalculics with normal IQs who had neurological examinations. The tests are characterized and the results briefly described; some examples of concrete pathological solutions to test items are given. This investigation suggests that nearly 6% of children of the so-called normal population can be justifiably expected to have symptoms of developmental dyscalculia as defined in this study.
Ladislav Košč (Fri,) studied this question.