Behavioral studies have shown that while young infants can discriminate many different phonetic contrasts, a shift from a language-general to a language-specific pattern of discrimination is found during the second semester of life, beginning earlier for vowels than for consonants. This age-related decline in sensitivity to perceive non-native contrasts has been generally attested in monolinguals. In order to analyze the impact of bilingual exposure on the perception of native-sound contrasts and the early building of language-specific contrastive categories, four-monthold and eight-month-old infants from Spanish monolingual, Catalan monolingual and Spanish-Catalan bilingual environments have been tested with a familiarization-preference procedure on a vowel contrast present onlyin Catalan: /e/—/E/. As expected, younger infants were all able to perceive this contrast, independently of the language of exposure. However, by eight months, only infants from Catalan monolingual environments succeeded. Although the decline in sensitivity with the monolingual Spanish group was expected, the results with the bilingual group challenge the view that mere exposure is enough to maintain the capacity to perceive a contrast. An additional experiment at 12 months of age indicated that bilinguals finally regained discrimination. Together these results suggest a specific developmental pattern of perceptual reorganization in bilingual exposure.

Previous research data indicate that soon after birth, infants from monolingual families can discriminate utterances drawn from languages that differ prosodically, but discrimination between rhythmically similar languages, such as English and Dutch, has not yet been established by 2 months of age. In the case of bilinguals, the question of how early they can distinguish between the languages of exposure remains unanswered. The goal of this study was to analyze language discrimination capacities in 4‐month‐old bilingual infants simultaneously exposed to 2 Romance languages belonging to the same rhythmic category, Spanish and Catalan. Using a familiarization‐preference procedure, 2 groups of bilingual‐to‐be infants showed a capacity to discriminate between these 2 familial languages. Moreover, when compared with 2 groups of infants from monolingual environments, the size of the observed effects was the same. These results can be taken as initial evidence of an early capacity to distinguish languages in simultaneous bilingual exposure, thus challenging the hypothesis that language discrimination capacities are delayed in bilinguals.

Infants growing up in bilingual environments succeed at learning two languages. What adaptive processes enable them to master the more complex nature of bilingual input? One possibility is that bilingual infants take greater advantage of the redundancy of the audiovisual speech that they usually experience during social interactions. Thus, we investigated whether bilingual infants’ need to keep languages apart increases their attention to the mouth as a source of redundant and reliable speech cues. We measured selective attention to talking faces in 4-, 8-, and 12-month-old Catalan and Spanish monolingual and bilingual infants. Monolinguals looked more at the eyes than the mouth at 4 months and more at the mouth than the eyes at 8 months in response to both native and nonnative speech, but they looked more at the mouth than the eyes at 12 months only in response to nonnative speech. In contrast, bilinguals looked equally at the eyes and mouth at 4 months, more at the mouth than the eyes at 8 months, and more at the mouth than the eyes at 12 months, and these patterns of responses were found for both native and nonnative speech at all ages. Thus, to support their dual-language acquisition processes, bilingual infants exploit the greater perceptual salience of redundant audiovisual speech cues at an earlier age and for a longer time than monolingual infants.