SELECTIVE IMPAIRMENT AS EVIDENCE FOR MENTAL ORGANIZATION OF ARITHMETICAL FACTS - BB, A CASE OF PRESERVED SUBTRACTION

We report here the case of a patient (BE), suffering from a precocious evolving dementia with impaired arithmetic performance, who showed sp ecific and theoretical pertinent dissociations in basic mental arithme tic. First, in a task involving production of answers to simple arithm etic problems, a strong dissociation was found among operations: while multiplication was severely impaired, addition was, moderately and su btraction only slightly impaired. A second dissociation was found betw een problems potentially solvable by rules and the others, with the fo rmer being better preserved. Finally, in multiplication verification t asks, the rate and distribution of errors among problems were not diff erent from those observed in the multiplication production task. This pattern of performance like the one presented by the patient RG (Dagen bach and McCloskey, 1992), suggests first that stored arithmetical fac t representations are segregated by arithmetic operation and second th at a distinction has to be drawn between arithmetical rules and arithm etical: facts. Last, the parallelism of performance observed here in v erification and production tasks suggests that the same deficit(s) is (are) responsible for errors in both tasks.