A case of impaired syntactic processing of numerals

Abstract

We report a case who frequently misplaced digits in reading or writing tasks involving numerals, and discuss his numeral processing. The case was a 58-year-old, left-handed male who suffered from right hemiplegia, mild Broca aphasia and visual-spatial perception disabilities after a left putaminal hemorrhage. Numerals have two codes : one the Arabic code using Arabic numerals, and the other a verbal code which corresponds to reading out aloud. Most numeral processing tasks entail transcoding between the two codes. The patient's basic knowledge of numerals was intact, but he commonly erred in transcoding tasks : for example, he read aloud “ three hundred forty ” for “ 34 ”, and wrote “ 2105 ” when hearing “ two hundred fifteen ”. However, there was rarely any paralexia or paragraphia for digits, which confirms the dissociation of his two processing systems. In recent research on cognitive mechanisms of numeral processing, a distinction between lexical and syntactic processing has been proposed. On the basis of that, the patient's performance suggests that his syntactic processing of numerals is impaired. We think that, in both directions, transcoding between the two codes requires orientation to the spatial representation of the decimal system, and in this case we suggest the possibility that his deficits in operations involving internal spatial representation affect his syntactic processing.