Highly proficient bilinguals compensate language dominance effects with differential attentional resource allocation: Insights from pupillometry

Previous research using cued language switching paradigms has shown a reversed language dominance effect in highly proficient bilinguals, wherein the dominant language is most inhibited. This study investigated cued language switching in highly proficient Spanish–Basque bilinguals (N = 50) using pupillometry, a novel measure of switching cost that tracks cognitive load via pupil size. Response times during cued picture-naming showed faster responses on non-switch than switch trials and faster responses in Basque than in Spanish. These findings suggest balanced proficiency across languages, with Spanish showing overall slowed responses, indicating a reversed dominance effect. Pupil data revealed larger pupil responses for Basque, the less dominant language, suggesting greater cognitive load despite faster naming. This indicates more attentional allocation or activation of the non-dominant language during cued language switching. These results provide insights into the cognitive processes involved in bilingual switching and highlight the value of using pupillometry to explore bilingual language processing.