Relative language proficiency modulates BOLD signal change when bilinguals perform semantic judgments. Blood oxygen level dependent.

The effect of relative language proficiency on the spatial distribution and magnitude of BOLD signal change was evaluated by studying two groups of right-handed English-Mandarin bilingual participants with contrasting language proficiencies as they made semantic judgments with words and characters. Greater language proficiency corresponded to shorter response times and greater accuracy in the semantic judgment task. Within the left prefrontal and parietal regions, the change in BOLD signal was smaller in a participant's more proficient language. The least proficient performance was associated with right, in addition to left, inferior frontal activation. The results highlight the importance of taking into consideration nature of task and relative language proficiency when drawing inferences from functional imaging studies of bilinguals.