A controlled study of processing of semantic and syntactic information in Alzheimer's disease.

Several previous studies have suggested a possible dissociation in the ability of patients with Alzheimer's Disease (AD) to utilize syntactic versus semantic information. This report describes a controlled experimental investigation of AD subjects' ability to process syntactic and semantic information. Thirteen mildly and moderately impaired AD patients were compared with 17 age- and education-matched elderly controls. Two tasks required subjects to identify and correct sentential errors; a third was a homophone spelling task. Results of the first task indicated that AD subjects were equivalent to controls in their ability to detect various types of sentential errors. When performing the second task, AD subjects were impaired in their ability to correct both types of errors, although there was a tendency for better performance with syntactically-based corrections. The third (homophone-spelling) task did not reveal a statistically significant differential sensitivity of AD subjects to syntactic versus semantic information. However, there was again a tendency for the former to be more easily processed. Results are discussed in terms of possible mechanisms which may underlie variations in the language-related performance of AD subjects.