First-language and second-language eye movement reading behavior in monolingual and bilingual children and adults: A focus on word age of acquisition effects

Word age of acquisition (AoA) influences many aspects of language processing, including reading. However, reading studies of word AoA effects have almost exclusively focused on monolingual young adults, leaving their influence in other age and language groups little understood. Here, we investigated how age (childhood, young adulthood) and language background (monolingual, bilingual) influence word AoA effects during first-language (L1) and second-language (L2) reading. Using eye-tracking, we observed larger L1 word AoA effects in children versus adults (across both language backgrounds). Moreover, we observed larger L2 versus L1 word AoA effects in bilinguals (across both ages), with some evidence of heightened effects in bilingual adults (for late-stage reading only). Taken together, our findings suggest that word AoA exerts a stronger influence on reading during conditions of reduced lexical entrenchment, offering critical insights into how both developing and bilingual readers acquire and maintain word representations across their known languages.