The impact of language proficiency on the time course and neural basis of L2 semantic access in bilinguals

Aims: The present study aimed to explore the impact of L2 proficiency on the time course and neural basis of L2 semantic access. Methodology: Two groups of participants with either high or low L2 proficiency performed a picture-word semantic matching task (i.e. consistent vs. inconsistent), with their event-related potentials (ERP) responses being recorded. Two stimulus types, L2 words and L1 words, were investigated in two separate blocks. Here the L1 words were tested as a control condition. Data and Analysis: The ERP epochs time-locked to the onset of the word were analyzed within 300-600 ms both at the surface (i.e. mean amplitude and peak latency) and the source (i.e. source localization) level. Findings/Conclusions: In the L2, a reliable N400 effect (i.e. semantic incongruity effect) was found for both high and low L2 proficiency bilinguals. However, the difference waves showed that the N400 peak latency was much shorter and the mean amplitude within 300-600 ms was much larger in bilinguals with higher L2 proficiency. Source localization analysis found left insula cortex (Brodmann area 13, Low > High) to be responsible for this proficiency effect (i.e. a decrease in the activation of left insula at a higher proficiency level). In the L1, a reliable N400 effect was found for both participant groups, and the two groups were matched in the N400 peak latency and amplitude, and its neural source. Originality: This study provides further evidence for the neural substrates underlying the modulation of L2 proficiency in semantic access by using a more sensitive task (i.e. picture-word matching task), and the current results revealed the engagement of left insula for the first time.