Wednesday, October 27, 2010


Partly because I am quite maladroit at Spanish, and partly because Jared Diamond is on my list of 'Famous' Folks [October 3, 2010], I am posting an interesting article by Professor Diamond from the journal Science:

The Benefits of Multilingualism

Jared Diamond

Geography Department, University of California Los Angeles, Los Angeles, CA 90095-1524, USA.

Multilingualism—the ability to understand and speak several languages—is exceptional in the United States but common elsewhere, especially in small-scale traditional societies. For instance, once while I was camped with some New Guinea Highlanders conversing simultaneously in several local languages, I asked each man to name each language in which he could converse. It turned out that everyone present spoke at least 5 languages, and the champion was a man who spoke 15. What are the cognitive effects of such multilingualism? Recent studies (1–5) show that children raised bilingually develop a specific type of cognitive benefit during infancy, and that bilingualism offers some protection against symptoms of Alzheimer's dementia in old people.

Bilingual education is politically controversial in the United States. Even immigrants whose native language is not English often believe that their children should learn only English and will be confused by learning two languages simultaneously. Until the 1960s, research appeared to show that bilingual children acquired language more slowly than monolingual children and achieved smaller vocabularies. But other variables correlated with bilingualism in those early studies, such as schooling and parental socioeconomic status, confounded their interpretation. More recent studies, comparing subjects matched for those other variables, have found bilinguals and monolinguals to be largely similar in cognition and language processing (6–8).

The clearest difference identified by these studies involves an advantage that bilinguals have over monolinguals, rather than a disadvantage. Our minds are assaulted by varied sights, sounds, and other external sensory inputs, plus thoughts and proprioreceptive sensations (which make us aware of the relative positions of our own body parts) (see the figure). To succeed in doing anything at all, we must temporarily inhibit 99% of those inputs and attend to just 1% of them, and the appropriate choice varies with the circumstances. That selective attention involves a set of processes, termed executive function, that reside in the prefrontal cortex and develop especially over the first 5 years of life (9).

Multilingual people have a special challenge involving executive function. Monolinguals hearing a word need only compare it with their single stock of arbitrary phoneme (sound) and meaning rules, and when uttering a word they draw it from that single stock. But multilinguals must keep several stocks separate. For instance, on hearing the phonemes b-u-rr-o, a Spanish/Italian bilingual instantly interprets them to mean either "donkey," if the context is Spanish, or "butter," if the context is Italian. Multilinguals participating in a multilingual conversation, like my New Guinea Highland friends or shop assistants in Scandinavian department stores, switch frequently and unpredictably between their stocks of phoneme/meaning rules. As a result, multilinguals have constant unconscious practice in using the executive function system.

Recent studies assess this ability by assigning to subjects game-like tasks designed to be confusing, either because the task rules change unpredictably, or because the task presents misleading cues that must be ignored (1–3, 7, 8). For instance, children are shown cards depicting either a rabbit or a boat, colored either red or blue, with or without a star. If the card has a star, the children must sort cards by color; if a star is absent, they must instead sort cards by the object depicted. It turns out that monolingual and bilingual subjects are equally successful if the rule remains the same from trial to trial (e.g., "sort by color"), but monolinguals have more difficulty than bilinguals at accommodating to a switch in rules. Although success at these games won't by itself make one rich or happy, our lives are full of other misleading information and rule changes. If bilinguals' advantage over monolinguals in these games also applies to real-life situations, that could be useful for bilinguals.

While this superior executive function has been reported for bilinguals of all ages, results for the youngest and the oldest subjects are of particular interest. Kovács and Mehler (4, 5) tested confusing game tasks on "monolingual" infants and "crib bilingual" infants—i.e., infants reared from birth to hear and eventually to speak two languages, because mother and father speak to the infant in different languages. It might seem meaningless to describe infants who cannot speak as monolingual or bilingual. Actually, infants learn to discriminate the sounds of the language or languages heard around them and to ignore sound distinctions not heard around them. For instance, Japanese infants lose, and English infants retain, the ability to discriminate the liquid consonants l and r, which the Japanese language does not distinguish.

How can one test responses to speech by those preverbal infants? Kovács and Mehler (4, 5) devised a clever protocol in which infants looked for pictures of a puppet appearing on the left side of a computer screen. The infants were conditioned to anticipate the puppet by first hearing a nonsense trisyllable (e.g., "lo-lo-vu"). Within nine trials, both monolingual and bilingual infants learned to look toward the screen's left side when they heard that trisyllable. But when Kovács and Mehler changed the rules and made the puppet appear on the screen's right side after broadcasting a different trisyllable, the "bilingual" infants unlearned their previous lesson and learned the new response within six more trials. In contrast, the "monolingual" infants couldn't learn the new response even after nine trials. Evidently, shifting frequently and unpredictably between hearing two parental languages made "bilingual" infants better able to cope with other unpredictable rule changes.

Do these findings suggest that bilinguals have an advantage over monolinguals in negotiating our confusing world of changing rules, and not merely in the task of discriminating lo-lo-vu from lo-vu-lo? You readers may demand evidence of more tangible benefits before you commit yourselves to babbling in two different languages to your infant children. Hence, you may be more impressed by recent results suggesting a protective effect of lifelong bilingualism against symptoms of Alzheimer's disease (10). Among hundreds of elderly Canadian patients with a probable Alzheimer's diagnosis, bilingual patients showed their first symptoms at an age 5 years older than did monolingual patients matched in other respects. Canadian life expectancy is 79, hence a 5-year delay for people in their 70's translates into a 47% decreased probability that they will develop Alzheimer's symptoms at all before they die.

How might this be? A short answer is the aphorism, "Use it or lose it." Exercising body systems improves their function; not exercising them lets their function deteriorate. That's why athletes and musicians practice. It's also why Alzheimer's patients are encouraged to play brain-challenging games like bridge or to solve Sudoku puzzles. But bilingualism is arguably the most constant practice possible for the brain. Whereas even a Sudoku fanatic can spend only a fraction of a day on Sudoku puzzles, bilinguals impose extra exercise on their brain every minute of their waking hours. Consciously or unconsciously, the bilingual brain constantly has to decide: Shall I think, speak, or interpret sounds spoken to me according to the arbitrary rules of language A or language B?

There are other unanswered questions. If one extra language offers some protection, do two extra languages offer more protection? If so, is the relationship between protection and number of extra languages linear, sublinear, or supralinear? For example, if bilinguals get 5 years of protection from their one extra language, do Scandinavian shop assistants speaking five languages also get just 5 years of protection, or do they get 5 x 4 = 20 years of protection? If you, alas, were not raised as a crib bilingual, will learning a second language in school let you catch up? Do bilinguals' advantages in coping with rule changes and confusing cues extend beyond trivial game tasks to real-life situations, such as school success and understanding other peoples' mental states? What neural mechanisms underlie bilingualism's reported protection against Alzheimer's symptoms? These questions will be of theoretical interest to linguists, and of practical interest to parents wondering how best to raise their children.


· 1. E. Bialystok, Dev. Psychol. 46, 93 (2010). [CrossRef] [Web of Science] [Medline]
· 2. E. Bialystok, X. Feng, Brain Lang. 109, 93 (2009). [CrossRef] [Web of Science] [Medline]
· 3. E. Bialystok, M. Viswanathan, Cognition 112, 494 (2009). [CrossRef] [Web of Science] [Medline]
· 4. A. M. Kovács, J. Mehler, Science 325, 611 (2009).[Abstract/Free Full Text]
· 5. A. M. Kovács, J. Mehler, Proc. Natl. Acad. Sci. U.S.A. 106, 6556 (2009).[Abstract/Free Full Text]
· 6. E. Bialystok, Bilingualism and Development (Cambridge Univ. Press, New York, 2001).
· 7. S. M. Carlson, A. N. Meltzoff, Dev. Sci. 11, 282 (2008). [CrossRef] [Web of Science] [Medline]
· 8. A. Costa, M. Hernández, N. Sebastián-Gallés, Cognition 106, 59 (2008). [CrossRef] [Web of Science] [Medline]
· 9. T. Shallice, From Neuropsychology to Mental Structure (Cambridge Univ. Press, Cambridge, 1988)
· 10. E. Bialystok, F. I. Craik, M. Freedman, Neuropsychologia 45, 459 (2007). [CrossRef] [Web of Science] [Medline]

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