Dyscalculia: Impaired ability in numerical concepts. These inabilities arise as a result of primary neurological lesion, are syndromic (e.g., GERSTMANN SYNDROME ) or acquired due to brain damage.Learning Disorders: Conditions characterized by a significant discrepancy between an individual's perceived level of intellect and their ability to acquire new language and other cognitive skills. These disorders may result from organic or psychological conditions. Relatively common subtypes include DYSLEXIA, DYSCALCULIA, and DYSGRAPHIA.Trail Making Test: The subject's ability to connect 25 numbered and lettered circles in sequence in a specific length of time. A score of 12 or below is suggestive of organic brain damage.Serbia: A republic located south of HUNGARY, west of ROMANIA and BULGARIA, and part of the former YUGOSLAVIA. The capital is Belgrade.Stroop Test: Timed test in which the subject must read a list of words or identify colors presented with varying instructions and different degrees of distraction. (Campbell's Psychiatric Dictionary. 8th ed.)Mathematics: The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Size Perception: The sensory interpretation of the dimensions of objects.Developmental Disabilities: Disorders in which there is a delay in development based on that expected for a given age level or stage of development. These impairments or disabilities originate before age 18, may be expected to continue indefinitely, and constitute a substantial impairment. Biological and nonbiological factors are involved in these disorders. (From American Psychiatric Glossary, 6th ed)Neuropsychological Tests: Tests designed to assess neurological function associated with certain behaviors. They are used in diagnosing brain dysfunction or damage and central nervous system disorders or injury.Reaction Time: The time from the onset of a stimulus until a response is observed.Attention: Focusing on certain aspects of current experience to the exclusion of others. It is the act of heeding or taking notice or concentrating.