Automatic processing of Arabic digits in dyscalculia

Developmental dyscalculia is characterized by difficulties to process numerical symbols. It has been hypothesized that these difficulties might result from impairments in accessing numerical magnitude from symbols. However, the exact origin remains unclear as impairments could affect any process between the recognition of the symbol and the representation of its magnitude. We addressed this issue in adults with a history of mathematical learning difficulties and performance below the norms in standardized arithmetic tests. In two independent studies, we showed that their difficulties extend to basic comparison tasks such as identifying which of two Arabic digits is larger in numerical magnitude. The first study indicated that these difficulties could not be explained by a failure to recognize symbols efficiently, as they had normal performance in a lexical decision task. The second study revealed typical stroop-like interference from irrelevant numerical cues in a physical size judgement, indicating automatic access to magnitude information. These results contradict the findings of previous studies and call for a re-examination of the cognitive processes behind the difficulties of people with dyscalculia in making sense of numerical symbols.