First Sounds, Second Language: How Word Onsets Spark Language Co-Activation in 3-Year-Old Bilinguals

Adult and young bilinguals co-activate their languages to different degrees, even in entirely monolingual tasks. However, many studies use translation pairs with high phonological overlap (e.g., the English-GERMAN: "milk"-"MILCH"), making it difficult to discern the origin of the co-activation. This study examined language co-activation in Catalan-Spanish bilingual toddlers using words with minimal phonological overlap across translations. Thirty Catalan-Spanish bilingual three-year-olds (N  =  30; M_age =  36.38 months, range = 35.57-37.43) participated in a visual word paradigm conducted entirely in Catalan, searching for an absent target named in Catalan (e.g., "apple" in Catalan: "poma," Spanish: "MANZANA") among images with labels that shared the initial phoneme across languages or were unrelated. The design included three types of images: (a) direct phonologically related (e.g., Spanish "PATO" for "duck"), (b) indirect phonologically related (e.g., Catalan "mitjó" for "sock"), and (c) unrelated (e.g., "brush," "sandwich"). If bilingual toddlers co-activate languages, they should look more at phonologically related than unrelated images due to shared phonological onsets. The results supported the hypotheses and provided solid evidence that young bilinguals co-activate phonologically related words in their familiar languages. Moreover, contrasting direct and indirect (translation-mediated) competitors showed that language co-activation unfolds dynamically, with timing shaped by the number of links involved.