Measuring second language proficiency with EEG synchronization: how functional cortical networks and hemispheric involvement differ as a function of proficiency level in second language speakers

This article examines the question of whether university-based high-level foreign language and linguistic training can influence brain activation and whether different L2 proficiency groups have different brain activation in terms of lateralization and hemispheric involvement. The traditional and prevailing theory of hemispheric involvement in bilingual language processing states that bilingual and second language processing is always at least in some form connected to the right hemisphere (RH), when compared to monolingual first language processing, the classical left-hemispheric language-processing domain. A widely held specification of this traditional theory claims that especially bilinguals or second language learners in their initial phases and/or bilinguals with poor fluency and less experience rely more on RH areas when processing their L2. We investigated this neurolinguistic hypothesis with differently proficient Austrian learners of English as a second language. Two groups of L2 speakers (all Austrian German native speakers), differing in their L2 (English) language performance, were recorded on electroencephalography (EEG) during the processing of spoken English language. A short comprehension interview followed each task. The `high proficiency group' consisted of English language students who were about to complete their master's degree for English language and linguistics, while the `low proficiency group' was composed of non-language students who had only school level performance and less training in English. The age of onset of L2 learning was kept constant: 9 years for both groups. To look for cooperative network activity in the brain, EEG coherence and synchronization measures were analysed for a high EEG frequency range (gamma band). Results showed the most significant group differences in synchronization patterns within the lower gamma frequency range, with more RH involvement (extensive right-hemisphere networks) for the low proficiency group, especially when processing their L2. The results can be interpreted in favour of RH theories of second language processing since, once again, we found evidence of more RH involvement in (late) second language learners with less experience and less training in the L2. The study shows that second language training (and resulting proficiency) and/or differences in ability or state of linguistic alertness can be made visible by brain imaging using newly developed EEG-synchronization techniques as a measure.