Abstract
Recent research has shown that extensive training in and exposure to a second language can modify the language organization in the brain by causing both structural and functional changes. However it is not yet known how these changes are manifested by the dynamic brain oscillations and synchronization patterns subserving the language networks. In search for synchronization correlates of proficiency and expertise in second language acquisition, multivariate EEG signals were recorded from 44 high and low proficiency bilinguals during processing of natural language in their first and second languages. Gamma band (30–45 Hz) phase synchronization (PS) was calculated mainly by two recently developed methods: coarse-graining of Markov chains (estimating global phase synchrony, measuring the degree of PS between one electrode and all other electrodes), and phase lag index (PLI; estimating bivariate phase synchrony, measuring the degree of PS between a pair of electrodes). On comparing second versus first language processing, global PS by coarse-graining Markov chains indicated that processing of the second language needs significantly higher synchronization strength than first language. On comparing the proficiency groups, bivariate PS measure (i.e., PLI) revealed that during second language processing the low proficiency group showed stronger and broader network patterns than the high proficiency group, with interconnectivities between a left fronto-parietal network. Mean phase coherence analysis also indicated that the network activity was globally stronger in the low proficiency group during second language processing.
Highlights
Most brain imaging studies on bilinguals/multilinguals have been conducted with either positron emission tomography (PET) or functional magnetic resonance imaging with a pure emphasis on localizing brain activities
EEG SYNCHRONIZATION RESULTS First we could differentiate first language (L1) from second language (L2) processing by gamma band global synchronization clustering patterns (CGMC) but on a more subtle scale, high proficiency (HP) and low proficiency group” (LP) bilinguals could further be significantly differentiated by bivariate gamma band synchronization measures predominantly, or, almost exclusively when processing L2
In the LP group one can see a marked increase in the left temporo-parietal/central region while listening to L2 English whereas the increase is much lower and right temporal for the listening of German (Figure 5). According to this result for the L1 we can assume that an increase up to 20% is within the statistical fluctuation, so that an increase of 25% or above might be considered significant
Summary
Most brain imaging studies on bilinguals/multilinguals have been conducted with either positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) with a pure emphasis on localizing brain activities (e.g., see De Bot, 2008 for review). They have not investigated the functional connectivity between different and distributed brain areas, yet one of the most discussed hypotheses – the influence of second language proficiency level on the extent and distribution of brain activation – would call for a method analyzing functional cooperation and interactions of brain areas. The second connectivity study (Majerus et al, 2008), albeit not investigating language or bilingual language processing per se but STM processing instead, could differentiate high from low proficiency bilinguals by www.frontiersin.org
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