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.