Age-of-acquisition Effects across the Adult Lifespan: Evidence from Eye Movements in Compound Word Reading

The Age of Acquisition (AoA) effect is where words acquired during childhood are recognised more quickly than those acquired during adulthood. However, the influence of AoA on compound words and its stability across the adult lifespan remain under-investigated. We conducted two eye-tracking experiments to clarify how the AoA effect is moderated by ageing and spacing. Ninety British English adults participated across two eye-tracking experiments: 60 young adults (30 reading unspaced compounds in Experiment 1 and 30 reading spaced compounds in Experiment 2) and 30 older adults (who read both unspaced and spaced compounds across experiments). Using Bayesian linear mixed-effects models, we observed a robust AoA effect in both spaced and unspaced compound words in young adults. However, in older adults, we only observed an AoA effect in unspaced compound words. The AoA effect declined with increasing age, whereas the slope of AoA effect was shallower in spaced than unspaced compound words. These findings suggest that the functional influence of AoA is contingent upon orthographic structure and reading experience: while whole-word AoA influences processing across visual formats in younger readers, older readers shift away from whole-word lexical properties toward constituent-level strategies when orthographic structure is disrupted by spacing.