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Bilingualism 101: Biological Basis of Bilingualism


Child bilingualism constitutes a significant global phenomenon which implies many societies worldwide to be multilingual. Thus, children encounter many languages which in turn play a crucial role into shaping their thought and mind. If on one hand children may hear two (or more) languages from birth, on the other they could also be reared bilingually despite not living in a bilingual family. This series of articles is therefore focused on bilinguals’ development and the mechanisms involved in the mastery of a plurality of linguistic codes.

The Bilingualism 101 series will be divided into the following chapters of content:

  1. Bilingualism 101: Bilingualism in Early Childhood

  2. Bilingualism 101: Biological Basis of Bilingualism

  3. Bilingualism 101: The Bilingual Brain

  4. Bilingualism 101: Bilingualism and Society

  5. Bilingualism 101: Bilingualism in Immigrants

  6. Bilingualism 101: Language Delay in Bilingualism

Biological Basis of Bilingualism

Within the context of second language acquisition the critical period hypothesis represents a highly debated topic. According to the definition given by Lenneberg (1967), this “automatic acquisition of a language” only occurs during a critical period (age 2 to puberty) after which language learning proceeds more slowly and proves less successful. The biological account as proposed by Lenneberg attributes the critical period to brain maturation and lateralisation of its functions in adults. Later literature provided some counterevidence to this biological account of the critical period (e.g., lateralisation in children happens earlier than the supposed end of the critical period proposed by Lenneberg). Moreover, Johnson and Newport (1989) formulated a “less-is-more” hypothesis, according to which language learning ability slows down due to the increase of other cognitive abilities. Whether the less-is-more hypothesis or any other theory about language learning (which holds true for second language acquisition as well) is accepted, there are necessary cognitive changes that happen. Those cognitive changes can be confirmed by the different neurological representation in language learners of different ages of acquisition (AoA).

Second language acquisition is a long-lasting learning process, by Stephen Andrews.

The common “younger is better” belief regarding bilinguals and their ability to learn more than one language is based on the AoA differences. The ongoing debate on this subject originated with Penfield and Roberts’ book Speech and Brain Mechanisms (1959) which proposed the early immersion education as the best solution for language learning. In 1967, Lenneberg used the term critical period hypothesis (CPH) for the first time in the context of language acquisition in his book. Subsequently, CPH, referring to the time of “automatic acquisition from mere exposure” in Lenneberg’s terms, rapidly gained importance. The article by Oyama (1978) describes it as a “sensitive” period in which “a certain type of developmental phenomenon” takes place. This work also focuses on further specifying the relation between the sensitive period and the psychological stage of the language learner, or as Kagan (1971, p. 998) expressed it:

”Biology has prepared the child for a change in cognitive structure, motivation, affect or behaviour, with experience playing the role of inducer. Exquisite, time-locked mechanisms alter the individual’s psychic competence so that he is able to react to evens in a new way”.

Moreover, as we can read in Hinde (1970, p. 556) “it is a useful working assumption that no particular case of learning would occur with equal facility at all stages of the life cycle […], the problem of sensitive periods for learning is the problem of ontogeny of behaviour itself”. It should be noted that the hypothesis holds true for both first and second language acquisition. The work by Emmorey, Bellugi, Friederici & Horn (1995) shows that the AoA effect (when the scarcity of input is not burdened with social deprivation) is crucial to the ultimate attainment in terms of language acquisition.

Language learning in bilingual children is a building process, by Cottonbro.

Since the late 1970s, a large amount of evidence confirms the robust negative correlation between AoA and L2 proficiency. The most common instrument for L2 proficiency assessment has been grammaticality judgements of auditory stimuli (i.e., oral task). Nonetheless, some researchers have used a picture-sentence matching test (Lee and Schachter, 1997) or a listening comprehension test with varying levels of white noise (Oyama, 1978); an inverse proportionality between AoA and L2 proficiency was still found, regardless of the assessment technique. As for phonological evidence of the effects of the critical period in language acquisition, many studies like the one by Neufeld (1988) have examined the pronunciation of subjects which differed in their age of first exposure to L2 via phonological competence measurement. The study in question demonstrated that being “accent free” in an L2 is statistically more probable for earlier AoA. Neurological data were used as well to confirm the age effects on language learning in bilinguals. For instance, the study by Kim, Relkin, Lee and Hirsch (1997) considered 12 highly proficient English L2 speakers of several L1 backgrounds who were engaged in a silent narration task. The study recorded the subjects’ brain activities in narrowly defined segments of Broca’s and Wernicke’s areas which revealed a significant difference in the location of the strongest activity within Broca’s area with respect to the age of first exposure to L2 (infancy and early adulthood were considered). So, AoA and ultimate attainment in terms of language proficiency seem to have a negative correlation, which is not caused by the amount of input and practice, sociopsychological variables, or other maturational issues. It seems more probable that a qualitative change in language learning capacity happens between 4 and 18 years.

An example of a grammar-based strategy for second language learning, by Olya Kobruseva.

Consequently, several studies tried to argue for the underlying reason that could explain this change. Bley-Vroman (1988) argued that a fundamental change happens in the sense that children use a different kind of learning strategy which is referred to as “domain-specific”, whereas adults use a problem-solving technique. Nonetheless, Ullman (2001) brought new neurolinguistic evidence, further specifying the difference in the learning process of children and adults in terms limitations: while children use implicit/procedural learning, adults use explicit/declarative learning. Moreover, evidence coming from different studies has shown that even if adults prove to be faster learners in the early stages of an L2 learning process than children, the latter are more capable in terms of ultimate attainment (whereas adults can more easily fall short of native speaker standards).

Organisation of brain areas is a cue that indicates their functioning, by Meo.

Thus, evidence shows how a limited developmental period before adulthood is related to an ultimate native-like level in terms of second language acquisition. Out of this developmental period, a complete mastery of an L2 doesnot seem possible. This hypothesis could hold true if seen in the light of critical periods observed in the development of many species. For instance, Marler (1991) described the innate ability of song learning in several species of birds, which follows a precise time schedule. Comparably, the work by Hubel and Wiesel (1965) demonstrated the necessity of a correct visual cortex stimulation before 3 months of age to obtain a fully developed vision in cats. On the contrary, in a study regarding our species, Curtiss (1977) found a correlation between pathologically low levels of grammatical development and a delayed first language acquisition. As already mentioned, Johnson and Newport (1989) contributed to collect counterevidence against the biological account. According to the authors, the less well-developed cognitive capacity in children is advantageous as far as language learning is concerned. Consequently, young learners usually engage in gradual and implicit learning, whereas adults are more prone to use explicit analytical skills. Lastly, children merely are less overloaded with information, thus managing to keep a broader learning window in comparison to adult learners.

The age of second language learning is crucial to the ultimate attainment, by Mikhail Nilov.

In conclusion, studies have clearly demonstrated differences between child and adult learners. The age of L2 acquisition proves crucial in determining whether the learners will fall short of a native-like level in terms of language performance. It appears that there is a fundamental plasticity in language learning during early childhood for reaching a native-like performance. It is highly probable that, due to their longer attentional span and to their cognitive executive abilities (i.e., higher level cognitive skills one uses to control and coordinate behaviours), adult learners use different learning and processing strategies, regardless of the hypothesis for language learning which is assumed as true.

Bibliographical references

Bley-Vroman, R. (1988). The fundamental character of foreign language learning. Grammar and second language teaching: A book of readings, 19-30. Curtiss, A. (1977). Genie: A Linguistic Study of a Modern Day. Wild Child. Hinde, R. A. (1970). Animal Behaviour (Second Edition). McGraw Hill. Hubel, D. H., & Wiesel, T. N. (1965). Binocular interaction in striate cortex of kittens reared with artificial squint. Journal of Neurophysiology, 28(6), 1041–1059. Johnson, J. S., & Newport, E. L. (1989). Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cognitive Psychology, 21(1), 60–99. Kagan, J. (1971). A conception of early adolescence. Daedalus, 997-1012. Kim, K., Relkin, N., Lee, K. M., & Hirsch, J. (1997). Distinct cortical areas associated with native and second languages. American Journal of Ophthalmology, 124(6), 868. Kroll, J. F., & Groot, A. D. M. B. (2009). Handbook of Bilingualism: Psycholinguistic Approaches (1st ed.). Oxford University Press. Lenneberg, E. H. (1967). The biological foundations of language. Hospital Practice, 2(12), 59-67. Livingston, R. B. (1959). Speech and Brain-Mechanisms . Wilder Penfield and Lamar Roberts. Princeton University Press, Princeton, N.J., 1959. xiii+286 pp. Illus. $6. Science, 129(3365), 1731–1732. Marler, P. (1991). Song-learning behavior: The interface with neuroethology. Trends in Neurosciences, 14(5), 199–206. Neufeld, G. G. (1988). Phonological Asymmetry in Second-Language Learning and Performance. Language Learning, 38(4), 531–559. Oyama, S. (1978). The Sensitive Period and Comprehension of Speech. NABE Journal, 3(1), 25–40. Penfield, W., & Roberts, L. (2014). Speech and brain mechanisms. In Speech and Brain Mechanisms. Princeton University Press. Ullman, M. T. (2001). The neural basis of lexicon and grammar in first and second language: the declarative/procedural model. Bilingualism: Language and Cognition, 4(2), 105–122.

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Antonio Verolino

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