Production of complex syntax in normal ageing and alzheimer's disease

Abstract

Word-finding difficulties are among the earliest symptoms of Alzheimer's disease (AD), but most AD patients retain the ability to produce well-formed sentences until the late stages of their disease. This dissociation has been used to argue for a modular distinction between grammar and the lexicon. In this paper, we offer an alternative view. First, we show that grammatical production is impaired in AD patients when grammar is assessed under highly constrained conditions in a film description task. Furthermore, these grammatical deficits are comparable in some respects to the patterns of lexical impairment observed in this and other studies of AD; specifically, patients do not produce frank lexical or grammatical errors, but they do find it difficult to access the “best fit” between meaning and form. We propose that differences in the onset time for lexical and grammatical symptoms in AD are due not to a disconnection between modules, but to fundamental differences in the automaticity and/or accessibility of content words and grammatical structures within a unified lexicon that breaks down gradually across the course of this disease.