The contribution of early language exposure to the cortical tracking of speech

Despite the relevance of the cortical tracking of speech for the development of speech perception skills, no study to date has explored whether and how it is shaped by language experience and exposure. In this study we expand the current theories of cortex-speech tracking by showing that the cortical tracking of speech in unbalanced bilingual children is modulated by language exposure. We recorded electroencephalography in 35 Basque-Spanish bilingual children (6 y.o.) with a markedly unbalanced bilingual profile (>70 % exposure to Basque; <30 % to Spanish) while they listened to continuous speech in each of their languages. We assessed their cortical tracking of speech at the acoustic temporal (speech envelope), lexical (lexical frequency), and semantic (sentence-level semantic distance) levels. Phase alignment between the speech envelope and the EEG activity (speech-brain coherence) in the delta frequency band (0.5 – 1.5 Hz) was significant and similar in both languages. Interestingly, mTRF modeling showed that the cortical encoding of the speech envelope in the language with the least exposure was the most robust. Moreover, mTRF modeling showed that children had a more sensitive cortical tracking of semantic information in their most experienced language. Lastly, only for the language with dominant exposure, the cortex-speech tracking of the envelope was linked to the phonological abilities, while their cortical tracking of lexico-semantic information predicted their vocabulary knowledge. Our findings inform the developmental theories by showing that the cortical tracking of acoustic temporal and lexico-semantic speech features depends on the accumulated experience within a language during the early years of language acquisition.