Processing lexicality in healthy aging and Alzheimer's disease: P3 ERP amplitude as an index of lexical categorization.

To explore how processing lexicality may change with aging and in the presence of Alzheimer's disease (AD), we conducted two experiments investigating lexicality judgements using an on-line behavioural psycholinguistic methodology and electrophysiological/event-related potential (ERP) methods; oddball lexical decision tasks. Results from these lexical decision tasks showed that while those with AD show similar rates of accuracy for their lexical decision as compared older adults (OA), they are particularly slowed when making judgements for pseudowords. Our results from the ERP tasks also showed that the two groups behaved differently with regard to elicitation of the P3 ERP response, which indicates differences in how these two groups form lexical categories. The pattern of ERP responses suggests that older adults are sensitive to the orthography/phonology of the stimuli during the course of lexical processing as compared to participants with AD who show less sensitivity to orthographic/phonological cues. Additionally, the ERP P3 amplitude results suggest further linguistically related differences between healthy older adults and those with AD, and highlight the importance and usefulness of combining behavioural psycholinguistic and ERP methodologies. [ABSTRACT FROM AUTHOR]