Diffindo! Precise language comprehension in older adulthood revealed by event-related brain potential studies of domain knowledge.

Knowledge accumulates across the lifespan, yet most research into its effects on language comprehension has focused on young adult college students. This leaves a critical gap in understanding how knowledge impacts comprehension in other populations, including healthy older adults. Older adults bring greater language experience and knowledge to comprehension tasks but also must contend with changes in cognitive factors like processing speed and working memory. We still know little about how older adults use their knowledge in real time and thus how basic comprehension abilities, which seem relatively stable across the adulthood, may arise from the use of different types of representations or processing mechanisms. To address this, we assessed levels of domain-specific knowledge (in this case, of the fictional world of Harry Potter; HP) and used event-related potentials to measure how that knowledge influenced language processing dynamics as older adults (ages 50-81 years) read HP-related sentences. For sentences ending with expected information (true HP "facts"), greater domain knowledge was associated with larger effects of contextual support on the N400, an ERP component linked to semantic access. However, older adults did not show domain knowledge-based N400 modulations to infelicitous but contextually related words, suggesting that they tended to maintain a narrower scope of semantic activation. By contrast, an analysis of trial-level back-sorted according to accuracy on a subsequent sentence-completion task revealed that when older adults could produce the correct sentence completion, domain knowledge did increase the tendency to activate broadly, possibly suggesting that high-knowledge individuals had engaged more actively in anticipatory processing. We suggest that comprehension mechanisms among older adults may capitalize on maturing semantic networks, which become functionally organized for more selective but accurate processing.