ABSTRACT
The lexico-semantic model has been used by researchers to describe most types of bilinguals. This chapter explores the respective effects of age of acquisition and language proficiency on developing concept mediation. The findings reveal heritage speakers' response times generally match the predictions of the concept mediation model irrespective of proficiency, with the exception of extremely low proficiency speakers. The concept mediation model, however, predicts little or no difference between picture prompts and L1-word prompts when the task is to produce the L2. For heritage speakers, acquisition of the first language either halts or regresses, and the L2 becomes the dominant language. The findings reveal heritage speakers' response times generally match the predictions of the concept mediation model irrespective of proficiency, with the exception of extremely low proficiency speakers. The pedagogical implications are far-reaching for both heritage language learners and language teachers, especially those who teach heritage learners.
