EXPRESS: Influence of word Age-of-Acquisition (AoA), vocabulary size, formal-lexical similarity, and semantic richness of words on lexical recognition and production: A study on foreign-word training.

A distinctive feature of the lexicon is its susceptibility to the order in which words are acquired; those learned earlier are accessed and retrieved more quickly than those acquired later-a phenomenon known as the age of acquisition (AoA) effect. This study investigates how vocabulary size (i.e., word-set size), formal-lexical similarity (i.e., neighbourhood density), and semantic richness (i.e., number of meanings) influence the AoA effect in lexical recognition and production. Three experiments were conducted with Spanish-speaking participants learning Welsh words in a controlled laboratory setting. Some words ("early") were trained from the outset, while others ("late") were introduced later and interleaved with the early words. Experiment 1 (47 participants) explored the relationship between AoA and vocabulary size, showing that vocabulary size has a strengthening modulatory effect on the AoA effect in lexical decision accuracy, although the interaction was only marginally significant. Experiment 2 (27 participants) examined formal-lexical similarity, finding that AoA is unaffected by neighbourhood density. Experiment 3 (18 participants) assessed semantic richness, showing that AoA effects are modulated by the number of meanings a word possesses in a task-dependent manner: an AoA effect emerged only for two-meaning words in lexical decision, whereas it was observed only for one-meaning words in picture naming. Overall, the results provide mixed evidence for the AoA effect in word production and recognition, primarily influenced by semantic richness and task demands. While the findings mainly support the mapping hypothesis, they also challenge certain predictions derived from it, as well as from the semantic and integrated accounts.