´ ´ Agnes Melinda Kovacs1 and Jacques Mehler
Cognitive Neuroscience Sector, Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 4, 34014 Trieste, Italy Edited by Susan E. Carey, Harvard University, Cambridge, MA, and approved February 12, 2009 (received for review November 11, 2008)
Children exposed to bilingual input typically learn2 languages without obvious difﬁculties. However, it is unclear how preverbal infants cope with the inconsistent input and how bilingualism affects early development. In 3 eye-tracking studies we show that 7-month-old infants, raised with 2 languages from birth, display improved cognitive control abilities compared with matched monolinguals. Whereas both monolinguals and bilinguals learned torespond to a speech or visual cue to anticipate a reward on one side of a screen, only bilinguals succeeded in redirecting their anticipatory looks when the cue began signaling the reward on the opposite side. Bilingual infants rapidly suppressed their looks to the ﬁrst location and learned the new response. These ﬁndings show that processing representations from 2 languages leads to a domain-generalenhancement of the cognitive control system well before the onset of speech.
cognitive development early bilingualism tracking infant cognition executive functions eye-
hen I was talking to my paternal grandmother I had to speak in a manner that I later discovered was called English, and when I was talking to my mother or her parents I had to talk a language that afterward turned out to beSpanish’’ notes J. L. Borges (1). In contemporary societies many children grow up in bilingual families and are faced with similar situations. Just like the young J. L. Borges they successfully learn to cope with different languages. However, a single language milieu is still the standard model for investigating language acquisition even though a great proportion of children are raised with morethan 1 language (2). Whereas infants who have to acquire 2 languages simultaneously face an important challenge, they pass language production milestones at an age similar to monolinguals (3), and display minor differences in language processing (4, 5). The present study investigates the mechanisms that bilingual infants might employ to deal efficiently with a linguistic signal coming from 2languages. Previous studies have shown that infants process various aspects of the languages they are exposed to from very early on. Indeed, neonates can discriminate utterances from 2 languages of different rhythmic classes (6–8). Two- to four-month-olds learn to distinguish languages belonging to the same rhythmic class (4, 9). Later on, in the second half of their first year, infants showexposure-dependent changes in phonetic discrimination (10, 11). These studies suggest that well before infants start speaking they have already acquired crucial properties of their maternal language. How do bilingually raised infants, who lack the homogeneous input of monolinguals, cope with their linguistic environment? We suggest that preverbal bilinguals using their ability to differentiate utterances from2 languages already build separate representations for each of the languages. Earlier proposals have suggested that during speech production bilinguals must continuously control their 2 languages to access the linguistic representations of the target language while avoiding interference from the nontarget language (12). Thus, to efficiently manage 2 languages bilingual speakers must employ theircognitive control abilities. In fact, cognitive control or executive functions (EF) refer to mechanisms involved in conflict monitoring, planning, attentional control, and the suppression (inhibition) of habitual
6556 – 6560 PNAS April 21, 2009 vol. 106 no. 16
responses (13, 14). Previous research has shown that the habitual use of 2 languages leads to improved cognitive control in...