Different neural mechanisms for rapid acquisition of words with grammatical tone in learners from tonal and non-tonal backgrounds: ERP evidence

Initial second language acquisition proceeds surprisingly quickly. Foreign words can sometimes be used within minutes after the first exposure. Yet, it is unclear whether such rapid learning also takes place for more complex, multi-layered properties like words with complex morphosyntax and/or tonal features, and whether it is influenced by transfer from the learners' native language. To address these questions, we recorded tonal and non-tonal learners' brain responses while they acquired novel tonal words with grammatical gender and number on two consecutive days. Comparing the novel words to repeated but non-taught pseudoword controls, we found that tonal learners demonstrated a full range of early and late event-related potentials in novel tonal word processing: an early word recognition component (similar to 50 ms), an early left anterior negativity (ELAN), a left anterior negativity (LAN), and a P600. Non-tonal learners exhibited mainly late processing when accessing the meaning of the tonal words: a P600, as well as a LAN after an overnight consolidation. Yet, this group displayed correlations between pitch perception abilities and ELAN, and between acquisition accuracy and LAN, suggesting that certain features may lead to facilitated processing of tonal words in non-tonal learners. Furthermore, the two groups displayed indistinguishable performance at the behavioural level, clearly suggesting that the same learning outcome may be achieved through at least partially different neural mechanisms. Overall, the results suggest that it is possible to rapidly acquire words with grammatical tone and that transfer plays an important role even in very early second language acquisition.