When a second language hits a native language. What ERPs (do and do not) tell us about language retrieval difficulty in bilingual language production

The accumulating evidence suggests that prior usage of a second language (L2) leads to processing costs on the subsequent production of a native language (L1). However, it is unclear what mechanism underlies this effect. It has been proposed that the L1 cost reflects inhibition of L1 representation acting during L1 production; however, previous studies exploring this issue were inconclusive. It is also unsettled whether the mechanism operates on the whole-language level or is restricted to translation equivalents in the two languages. We report a study that allowed us to address both issues behaviorally with the use of ERPs while focusing on the consequences of using L2 on the production of L1. In our experiment, native speakers of Polish (L1) and learners of English (L2) named a set of pictures in L1 following a set of pictures in either L1 or L2. Half of the pictures were repeated from the preceding block and half were new; this enabled dissociation of the effects on the level of the whole language from those specific to individual lexical items. Our results are consistent with the notion that language aftereffects operate at a whole-language level. Behaviorally, we observed a clear processing cost on the whole-language level and a small facilitation on the item-specific level. The whole-language effect was accompanied by an enhanced, fronto-centrally distributed negativity in the 250-350 ms time-window which we identified as the N300 (in contrast to previous research, which probably misidentified the effect as the N2), a component that presumably reflects retrieval difficulty of relevant language representations during picture naming. As such, unlike previous studies that reported N2 for naming pictures in L1 after L2 use, we propose that the reported ERPs (N300) indicate that prior usage of L2 hampers lexical access to names in L1. Based on the literature, the after-effects could be caused by L1 inhibition and/or L2 interference, but the ERPs so far have not been informative about the causal mechanism.