Referential communication in Alzheimer's type dementia

This paper investigates factors that underlie reduced informative content and lack of reference in the discourse of patients with Alzheimer's Type Dementia (DAT). Patients with DAT, fluent aphasics and normal controls were given a referential communication task structured to assess lexical encoding of information, pragmatic/conceptual elaboration of information and effectiveness in establishing reference. The subjects also received standardised aphasia tests (CADL, Holland, 1980; and Cookie Theft Picture Description, Nicholas and Brookshire, 1993). Comparable reduction of lexical encoding of information was found in the discourse of aphasic and DAT participants both on the referential communication task measures and on the standardised evaluation with the Cookie Theft Picture Description test. However, the DAT subjects' discourse on the referential communication task was less efficient in establishing reference than that of the aphasics since the former presented more misunderstandings and required more explicit prompts from the listener. Furthermore, the DAT language on the referential communication task contained confounding and irrelevant information; also, the number of these errors correlated negatively with their referring abilities. Results of the CADL test confirmed that the DAT participants had less communicative effectiveness than their lexical deficit alone predicted. Finally, examination of the performance of individual DAT subjects showed that lexical encoding of information could dissociate from effectiveness in making reference. These findings support the view that difficulty in pragmatic/conceptual elaboration of discourse information content plays a substantial role in the development of reduced information content and lack of reference of DAT "empty speech". These results are discussed in the framework of the hypothesis of early attentional/executive impairment in DAT (Perry and Hodges, 1999).