Different languages in one brain: an ERP study on simultaneous interpreters

The aim of the present study was to investigate the neurofunctional mechanisms of orthographic analysis and lexical access in multilingual people. Professional simultaneous interpreters took part to the experiment. In order to distinguish the role played by the age of acquisition and proficiency of a certain language, we selected fifteen Italian native speakers with an excellent proficiency in English (L2) and an intermediate knowledge of German (L3). 780 linguistic stimuli were created. They consisted of words (balanced in terms of imageability and frequency of use) and legal pseudo-words in 3 different languages (Italian, English and German). All stimuli were balanced in terms of length and position of target letter (beginning, middle or end of stimulus). The task consisted in responding to the appearance of given target letter. EEG was recorded from 30 scalp sites at a sampling rate of 512 Hz. ERPs were time-locked to stimulus onset. Both reaction times (RTs) and electrophysiological data indicated that the difference between words and legal pseudo-words (the so called "word superiority effect") was modulated by language age of acquisition and proficiency. Words were discriminated from pseudo-words as early as 150 ms with larger N1 responses to words over the left inferior posterior occipital area, possibly indexing the activity of the so-called VWFA, only in the native language (L1). At later processing stages (since 250 ms), corresponding to deeper linguistic processing, we observed a clear difference in the brain response to languages mastered with a different degree of proficiency (namely English vs. German), both at posterior (N2 and N3 component) and anterior (LPN component) electrode sites areas. These data show how ERPs can dissociate age of acquisition from proficiency, and be predictive of a person linguistic competence.