Ultra-Rapid and Automatic Interplay Between L1 and L2 Semantics in Late Bilinguals: EEG Evidence
Background: Converging behavioral and neuroimaging evidence shows that bilinguals activate both their native (L1) and second (L2) language during linguistic processing, suggesting that L1 and L2 may share neural lexicon. Previous studies have typically reported the modulation of the N400, an ERP component related to semantic access, as a neural correlate of such L1-L2 interplay, indicating a shared activation of conceptual memory representations. Such a late effect (~400 ms post-stimulus onset) likely reflects controlled and post-lexical processes, in contrast to earlier modulations (<100 ms), found in monolinguals and indicative of fast and automatic lexico-semantic L1 access.
Methods: The present EEG study examined early neurophysiological crosslinguistic activation during bilingual word access. A 128-channel EEG system was used to record brain signals from 17 late bilinguals during a masked-priming crosslinguistic task in which L1 (Russian) words were presented as subliminal primes for 50 ms before L2 (English) target words. Participants read the targets silently and occasionally responded to catch stimuli. Critically, prime-target L1-L2 pairs overlapped only phonologically, only semantically, both phonologically and semantically, or did not overlap. Cluster-based random permutation analyses were implemented to examine the effects of both semantic and phonological crosslinguistic similarity at two long ERP segments, corresponding to early (20 – 200 ms) and late (300 – 500 ms) stages of word access.
Results: Analyses on the early temporal segment revealed a significant cluster for the main effect of semantic similarity (p=0.033) at 40–60 ms over centro-posterior scalp sites, reflecting a more positive amplitude for semantic dissimilarity than for semantic similarity. Importantly, neural source reconstruction at this latency revealed activations within a left-hemispheric network including middle temporal gyrus (BA 21), primary auditory cortex (BA 41), and angular gyrus (BA 39) as the most likely neural substrate of the early semantic effect. Furthermore, analyses carried out at the late temporal segment revealed significant clusters over frontocentral sites for the main effect of semantic (p=0.048) and phonological similarity (p=0.006), at 312–356 and 380–444 ms respectively, thus replicating previous N400 crosslinguistic effects.
Conclusions: Our findings confirm the existence of an integrated brain network for bilingual lexicon and reveal the earliest (~50 ms) crosslinguistic effect reported so far, suggesting fast and automatic L1-L2 interplay during semantic word access. This study has been supported by a Russian Science Foundation Grant (№19–18-00550) awarded to HSE University.