Language switching mechanisms in simultaneous interpreters: an ERP study.

Recent event-related potential (ERP) and neuroimaging studies suggest that bilingual individuals are able to inhibit the processing of a non-target language while speaking or reading in another language. The neural mechanisms subserving code switching still remain matter of debate. The aim of the present study was to shed some light on the neurofunctional bases of such mechanisms. ERPs were recorded in native Italian simultaneous interpreters and monolingual controls during a semantic processing task in which the subjects had to evaluate the sensibleness of final words of incomplete sentences. All participants were strictly right-handed. Interpreters knew at least four languages (from four to eight) at a professional level, from among 11 European and Asian languages, and had an excellent command of English (L2). Four hundred short sentences were presented visually; half of them had an unexpected final word, producing a semantic incongruence. Sentences could be entirely in Italian or in English (unmixed); alternatively, the body of the sentence could be in English and the final word in Italian or vice versa (mixed). ERPs were time locked to the onset of the final word. Both reaction times (RTs) and electrophysiological data indicated a lesser degree of hemispheric lateralization for linguistic function during L2 rather than L1 processing in interpreters. The first effect of lexical switching and code switching was recorded in the time window between 140 and 200 ms at left anterior sites. At N400 level, ERPs were significantly larger to L2 than to L1 words only in the mixed and not in the unmixed condition. No effect of language was observed in the unmixed condition, thus suggesting that the difference in L1/L2 processing was not related to a difference in proficiency, but rather to a different functional organization of semantic integration systems due to the later age of acquisition of L2 compared to L1. Interpreters were faster at reading and comprehending sentences in English ending with an Italian word than vice versa (L2 --> L1 switch).