How does the bilingual experience sculpt the brain?

Abstract

The ability to speak two languages often marvels monolinguals, although bilinguals report no difficulties in achieving this feat. Here, we examine how learning and using two languages affect language acquisition and processing as well as various aspects of cognition. We do so by addressing three main questions. First, how do infants who are exposed to two languages acquire them without apparent difficulty? Second, how does language processing differ between monolingual and bilingual adults? Last, what are the collateral effects of bilingualism on the executive control system across the lifespan? Research in all three areas has not only provided some fascinating insights into bilingualism but also revealed new issues related to brain plasticity and language learning.

Figure 1. Two experiments comparing monolingual and bilingual infants’ capacities to discriminate languages

(A) A study presented 4-5 month old monolingual and bilingual Spanish-Catalan infants with English sentences (an unknown language to the infants) or with sentences of their maternal language (either Spanish or Catalan). Sentences from each language could randomly appear from the right or from the left from loudspeakers hidden behind pictures of women. Previous research with monolingual infants had established that infants orientate their gaze faster to familiar than to unfamiliar languages. Indeed, monolingual Catalan and monolingual Spanish infants displayed the expected pattern (in blue in the figure). However, Spanish-Catalan bilingual infants showed the opposite pattern, and they oriented faster to the unknown language than to the maternal one. (B) In other studies infants were familiarized with silent video-clips of individuals speaking either French or English. Infants first saw silent video clips of three different French-English bilingual speakers speaking either in French or in English and their attention to the images was measured (looking times). Once their attention declined (habituation criterion) half of the infants saw new sentences in the same language and half of the infants saw new sentences in the other language. At the test phase monolingual and bilingual infants before the age of 8 months looked longer when presented with video clips from a different language from the one in the familiarization phase, indicating that all infants were able to discriminate the languages. However, at 8 months of age, only bilingual infants seem to be able to discriminate between the silent video-clips^, . Furthermore, previous experience with the languages of the silent video-clips does not have any significant influence on the capacity of bilingual 8-month-olds to discriminate them. The capacity to visually discriminate French from English is equivalent for infants exposed to French and English and for infants exposed to Spanish and Catalan. The figure shows the results of the monolingual and bilingual infants that saw the new sentences. It is shown the increment (or decrement) in looking times between the last trials of the habituation phase and the trials in the test phase (when a language change was introduced). As it can be seen, only bilingual 8-month olds significantly increased their looking times.