Age-related effects on lexical, but not syntactic, processes during sentence production

We investigated the effect of healthy ageing on the lexical and syntactic processes involved in sentence production. Young and older adults completed a semantic interference sentence production task: we manipulated whether the target picture and distractor word were semantically related or unrelated and whether they fell within the same phrase (“the watch and the clock/hippo move apart”) or different phrases (“the watch moves above the clock/hippo”). Both age groups were slower to initiate sentences containing a larger, compared to a smaller, initial phrase, indicating a similar phrasal scope of advanced planning. However, older adults displayed significantly larger semantic interference effects (slower to initiate sentences when the target picture and distractor word were related) than young adults, indicating an age-related increase in lexical competition. Thus, while syntactic planning is preserved with age, older speakers encounter problems managing the temporal co-activation of competing lexical items during sentence production.