Language exposure, input diversity and receptive vocabulary affect stop and vowel perception in Spanish-dominant Spanish-English bilingual children

Language-specific speech perception intensifies at preschool age; yet no study has examined this phenomenon in bilinguals. This study explores stop and vowel perception in English and Spanish in 74 Mexican-origin children (mean age: 50 months; 37 Spanish-English bilinguals, 24 females; 37 English monolinguals, 23 females) and examines whether language exposure, input diversity, and receptive vocabulary moderate bilinguals' perception in each language. Bilinguals' English stop—but not vowel—perception, as assessed through a forced-choice minimal-pair identification task in 2022 and 2023, was partially affected by Spanish, suggesting subtle bilingual–monolingual differences. The effect of input diversity on perception was mediated by vocabulary in English and exposure in Spanish, highlighting the complex interplay of input- and proficiency-­related variables on bilingual perception.