Differential age effects on lexical ambiguity resolution mechanisms.

Multiple neurocognitive subsystems are involved in resolving lexical ambiguity under different circumstances. We examined how processing in these subsystems changes with normal aging by comparing ERP responses to homographs and unambiguous words completing congruent sentences (with both semantic and syntactic contextual information) or syntactic prose (syntactic information only). Like young adults in prior work, older adults elicited more negative N400s to homographs in congruent sentences, suggesting mismatch between the context and residual activation of the contextually irrelevant sense. However, the frontal negativity seen in young adults to homographs in syntactically well-defined but semantically neutral contexts was absent in older adults as a group, suggesting a decline in recruiting additional neural resources to aid difficult semantic selection. A subset of older adults with high verbal fluency maintained a young-like effect pattern.