Meanings within words: How Chinese bilingualism shapes the neural basis of English morphological processing in preschoolers.

Preschool is a crucial developmental period during which children advance their spoken language skills that prepare them for later reading acquisition. During this period of rapid growth, bilingual experience fosters cross-linguistic interactions that shape distinctive neural architecture for language. This study explored cross-linguistic transfer by probing the developing bilingual brain basis for morphological processing, which emerges during the preschool years and supports reading development. While neural activation was measured with fNIRS, Chinese-English bilingual and English monolingual children (N = 155, ages 3-5) completed an English morphological word processing task that captures word roots (e.g., in compound words like 'gold-fish') and affixes (e.g., in inflectional and derivational words like 'walk-ing', 'farm-er'). When processing word roots, bilinguals exhibited greater activation in the left middle temporal region, indicating enhanced semantic sensitivity compared to monolinguals. In contrast, when processing affix-based words, bilinguals showed greater left frontal activation, indicating enhanced morpho-analytical processing. Moreover, the brain-behaviour associations aligned with bilingual children's experience with Chinese, a language characterized by semantically transparent compound structures and the relatively limited derivational morphology. Higher Chinese proficiency was associated with decreased left inferior frontal activation for English word roots, suggesting that Chinese experience facilitates access to word roots. In contrast, higher Chinese proficiency was associated with increased left inferior frontal activation for English affixes, suggesting that Chinese experience yields enhanced analytical demands for affixes. These results strengthen evidence of cross-linguistic transfer in the preschool years, and highlight how spoken language experience sculpts the brain for later language and literacy development.