Comprehension of long distance number agreement in probable Alzheimer's disease

Abstract

Two cross-modal naming experiments examined the role of working memory in processing sentences and discourses of various lengths. In Experiment 1, 10 memory impaired patients with probable Alzheimer's disease (AD) and 10 healthy elderly control participants showed similar sensitivity to violations of subject-verb number agreement in a short sentence condition and similar degradation to this sensitivity in a long sentence condition. Performance in neither length condition correlated with performance on working memory tasks, suggesting that the processes involved in interpreting a grammatical dependency between adjacent and nonadjacent elements are different from those required in the working memory tasks. In Experiment 2, the same 10 AD patients were less sensitive than the 10 control participants to pronounantecedent number agreement violations in a short discourse condition, but neither group was affected by additional length. In this experiment, performance in both the short and long conditions correlated with working memory performance. These results show that grammatical and discourse dependencies pose different memory and processing demands, and that these differences are not simply due to differences in the amount of intervening material between dependent words. The results also suggest that while the working memory deficits characteristic of AD do not interfere with on-line grammatical processing within sentences, they do compromise on-line discourse processing across sentences. Two cross-modal naming experiments examined the role of working memory in processing sentences and discourses of various lengths. In Experiment 1, 10 memory impaired patients with probable Alzheimer's disease (AD) and 10 healthy elderly control participants showed similar sensitivity to violations of subject-verb number agreement in a short sentence condition and similar degradation to this sensitivity in a long sentence condition. Performance in neither length condition correlated with performance on working memory tasks, suggesting that the processes involved in interpreting a grammatical dependency between adjacent and nonadjacent elements are different from those required in the working memory tasks. In Experiment 2, the same 10 AD patients were less sensitive than the 10 control participants to pronounantecedent number agreement violations in a short discourse condition, but neither group was affected by additional length. In this experiment, performance in both the short and long conditions correlated with working memory performance. These results show that grammatical and discourse dependencies pose different memory and processing demands, and that these differences are not simply due to differences in the amount of intervening material between dependent words. The results also suggest that while the working memory deficits characteristic of AD do not interfere with on-line grammatical processing within sentences, they do compromise on-line discourse processing across sentences.