From the app to the lexicon: Neurocognitive markers of word integration in a second language

The consolidation of newly learned vocabulary into semantic memory networks is a critical process in word learning, including second-language (L2) acquisition. However, most neurocognitive studies of lexical-semantic integration rely on short, artificial learning paradigms, leaving open the question of whether naturalistic, app-based learning produces comparable neural outcomes. In this study, we combined an ecological learning environment with controlled electrophysiological testing to examine whether vocabulary learned through Duolingo shows neural signatures of semantic integration. Native Spanish speakers studied Guarani vocabulary for five weeks and subsequently completed a semantic decision task during EEG recording that included both L1 (Spanish) and L2 (Guarani) word pairs. Critically, L2 targets were classified as remote (learned earlier during the five-week training and not practiced in the final stage) or recent (learned in the final training stage and tested approximately 10 days later), allowing us to assess consolidation-related differences. Behaviorally, participants responded more accurately and faster to L1 than L2 words, and accuracy for related items was higher for remotely than recently learned items, consistent with consolidation-related strengthening. Electrophysiologically, robust N400 priming effects emerged for remotely learned words—whereas no facilitation was observed for recent words. This graded pattern suggests that only words with extended consolidation time exhibited neural markers of lexical–semantic integration. Together, these findings demonstrate that combining real-world digital learning with controlled neural testing can reveal how naturalistic language experience shapes the neurocognitive dynamics of word learning and consolidation.