The effect of Alzheimer's disease and aging on conceptual combination

Alzheimer's disease (AD) subjects, healthy elderly, and young adults interpreted a series of novel noun-noun expressions composed of familiar object words. Subjects interpreted each item by selecting one of three possible definitions: a definition in which the referents of each noun were associated together in a particular context (e.g., rabbit cat: a cat that is raised by rabbits); a definition based on integrating the semantic attributes from each noun into a single referent (e.g., rabbit cat: a cat that has long ears and hops); and a semantic foil. The results show that the AD subjects selected significantly fewer integrational definitions and significantly more foils than healthy elderly subjects. Healthy elderly participants were also found to select significantly more foil definitions than the young adult subjects. These findings suggest that AD individuals have difficulty in integrating semantic features when interpreting novel noun-noun expressions and that both AD and healthy elderly individuals have morphosyntactic impairments related to the identification of the modifying and head nouns of noun-noun expressions.