The morphosyntax interface in patients with Alzheimer's disease.

This paper investigates the morphological competence of Italian-speaking patients diagnosed with Alzheimer’s Disease (AD). More specifically, we test whether and how AD patients can apply the morphological operations involved in complex word formation, i.e., conversion and affixation. The aims are twofold: (i) to detect whether morphological operations are impaired in this population and (ii) to determine whether word formation rules can be a useful marker in AD diagnosis. Previous studies on AD have reported that patients are impaired in various linguistic domains, but little is known about whether and how morphology is affected. This study reports the results of a picture-supported sentence completion task administered to 20 AD patients (MMSE score 0-24) and 20 neurologically age- matched healthy subjects. We found that AD patients’ performance differed from that of neurologically age-matched healthy participants in both the rate of accuracy and the morphological processes exploited to create complex words. While AD patients apply both conversion and affixation, the former operation was selectively applied to create complex verbs derived from nouns and the latter was applied to compose complex nouns from verbs. We conclude that both the low rate of accuracy and the selective application of the two morphological processes distinguish AD patients from neurologically age-matched healthy subjects and can thus be taken as markers in AD diagnosis. From a theoretical viewpoint, our results may suggest that conversion is a form of affixation, as proposed in various studies, e.g., Bauer (2008).