Transcoding zeros within complex numerals.

This paper describes a patient (LD) showing a selective syntactic deficit in the production of Arabic numerals. Unlike in previously reported cases, LD's syntactic difficulties result in deletions rather than insertions of zeros, with a reduction of the number magnitude. The pattern of errors highlighted a distinction between "lexical zeros", i.e. the zeros in tens, that are semantically derived, and "syntactic zeros" that are syntactically produced as the result of specific production rules. In LD, only syntactic zeros were affected. Furthermore, the processing of numerals with final zeros was found to be easier than the processing of numerals with internal zeros. This pattern of errors is compatible with the lexical-semantic model of Power and Dal Martello. In this model, in fact, lexical zeros originate from a numerical concept, while syntactic zeros originate from a concatenation operation, plus an overwriting operation leaving one or more intermediary zeros. Thus, lexical zeros may be easier to manipulate than syntactic zeros that merely represent a null quantity associated to a specific power of 10.