The effects of ageing and Alzheimer's disease on semantic and gender priming.

Normal ageing as well as age-associated pathological conditions, such as Alzheimer's disease, are associated with modifications of language processing. In particular, an impaired performance in semantic tasks, associated with relatively spared syntactic processing, has been suggested to be the hallmark of the language disorder of Alzheimer's disease. The present experiment tests semantic and syntactic aspects of language processing at the same time, using an on-line paradigm, in patients with Alzheimer's disease, compared with elderly and young controls. Normal ageing was associated with a profile of performance, which was slowed but qualitatively comparable with that of young controls. Both gender agreement and congruent sentential semantics resulted in facilitation relative to baseline in young and elderly controls, with no significant interference effects of incongruent grammatical and semantic information. In contrast, Alzheimer's disease patients presented both facilitation and interference effects. These findings suggest that interference effects are amplified by dementia, and may result from defective inhibitory processes due to Alzheimer's disease pathology.