The present investigation explored the relation between the amount of language input and neural responses in English monolingual (N = 18) and Spanish-English bilingual (N = 19) infants. We examined the mismatch negativity (MMN); both the positive mismatch response (pMMR) and the negative mismatch response (nMMR), and identify a relationship between amount of language input and brain measures of speech discrimination for native and non-native speech sounds (i.e., Spanish, English and Chinese). Brain responses differed as a function of language input for native speech sounds in both monolinguals and bilinguals. Monolingual infants with high language input showed nMMRs to their native English contrast. Bilingual infants with high language input in Spanish and English showed pMMRs to both their native contrasts. The non-native speech contrast showed different patterns of brain activation for monolinguals and bilinguals regardless of amount of language input. Our results indicate that phonological representations of non-native speech sounds in bilingual infants are dependent on the phonetic similarities between their native languages.