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The contribution of early language experience to the cortical tracking of speech: evidence from bilingual children
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Poster C91 in Poster Session C, Wednesday, October 25, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Jose Pérez-Navarro1, Nicola Molinaro1, Giorgio Piazza1, Anastasia Klimovich-Gray2, Mikel Lizarazu1, Marie Lallier1; 1Basque Center on Cognition, Brain and Language (BCBL), 2University of Aberdeen
The cortical tracking of speech is the temporal alignment of continuous brain activity to the information present in the speech signal. Cumulative evidence during the past decade has shown its relevance for supporting speech comprehension, as well as its atypical maturation in developmental language disorders (e.g., dyslexia). This neurocognitive mechanism is also in place and developing during infancy and childhood. However, no studies to date have addressed the question of whether accumulated language experience shapes the cortical tracking of acoustic and linguistic information from the speech signal. This was our main goal: to test whether bilingual children with considerably unbalanced experiences within each of their languages show different strategies for the cortical tracking of speech for each language respectively. We collected EEG data from 35 Basque-Spanish bilingual children (6 y.o.) with a markedly unbalanced bilingual profile (>70 % exposure to Basque, L1 hereafter; <30 % to Spanish, L2). Children listened to continuous speech in the form of two 14-minute stories (one in each language), which allowed us to assess their cortical tracking of speech at the acoustic temporal (speech envelope), lexical (lexical frequency), and semantic (sentence-level semantic distance) levels respectively. As indexes of the cortical tracking of speech, we computed speech-brain coherence and multivariate temporal response functions (mTRF). While speech-brain coherence measures the phase alignment between two signals (speech envelope and EEG activity), mTRF models the linear mapping between speech features (speech envelope, lexical frequency and semantic distance in our case) and changes in the continuous EEG signal. Through cluster-based permutation tests, we found significant speech-brain coherence in L1 and L2 within the delta frequency band (0.5 - 1.5 Hz), which aligns with prosodic phrasing in both languages. Despite robust speech-brain coherence in both languages, there were no significant between-languages differences regardless of the markedly bigger exposure to L1 than to L2. Nonetheless, the cortical mapping (mTRF) of the speech envelope yielded a significant between-languages difference. Namely, the cortical encoding of the speech envelope in L2 was more robust than in L1. There was also a strong significant between-languages difference in the temporal response to semantic distance. In this case, children showed a more sensitive early (70-230 ms) cortical tracking of semantic information in L1 than L2. We also found that, only in L1 (Basque), the cortical tracking of speech at the envelope level predicted phonological abilities; and the cortical tracking of lexico-semantic information predicted vocabulary knowledge. Our findings initially point at a tradeoff from relying on acoustic temporal (envelope) information (L1 < L2) and on more abstract linguistic (semantic) information (L1 > L2) that is dependent on the accumulated experience within a language during the early years of life. The specific relationships between the cortical tracking of speech and different language abilities highlight the behavioral relevance of the maturation of this neurocognitive mechanism for speech comprehension. The present study can inform developmental cognitive neuroscience and neurobiology of bilingualism by bringing to context the relevance of accumulated linguistic experience for the maturation of brain processing of language during childhood.
Topic Areas: Language Development/Acquisition, Multilingualism