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Monday, February 10, 2025

Hearing bilingual: how babies sort out language

by

20111015

Once, ex­perts feared that young chil­dren ex­posed to more than one lan­guage would suf­fer "lan­guage con­fu­sion," which might de­lay their speech de­vel­op­ment. To­day, par­ents of­ten are urged to cap­i­talise on that ear­ly knack for ac­quir­ing lan­guage.As the rel­a­tive­ly new sci­ence of bilin­gual­ism push­es back to the ori­gins of speech and lan­guage, sci­en­tists are teas­ing out the ear­li­est dif­fer­ences be­tween brains ex­posed to one lan­guage and brains ex­posed to two.Re­searchers have found ways to analyse in­fant be­hav­iour, where ba­bies turn their gazes, how long they pay at­ten­tion, to help fig­ure out in­fant per­cep­tions of sounds and words and lan­guages, of what is fa­mil­iar and what is un­fa­mil­iar to them.

Now, analysing the neu­ro­log­ic ac­tiv­i­ty of ba­bies' brains as they hear lan­guage, and then com­par­ing those ear­ly re­spons­es with the words that those chil­dren learn as they get old­er, is help­ing ex­plain not just how the ear­ly brain lis­tens to lan­guage, but how lis­ten­ing shapes the ear­ly brain.Re­cent­ly, re­searchers at the Uni­ver­si­ty of Wash­ing­ton used mea­sures of elec­tri­cal brain re­spons­es to com­pare so-called mono­lin­gual in­fants, from homes in which one lan­guage was spo­ken, to bilin­gual in­fants ex­posed to two lan­guages.Of course, since the sub­jects of the study, adorable in their in­fant-size EEG caps, ranged from six months to 12 months of age, they weren't pro­duc­ing many words in any lan­guage.Still, the re­searchers found that at six months, the mono­lin­gual in­fants could dis­crim­i­nate be­tween pho­net­ic sounds, whether they were ut­tered in the lan­guage they were used to hear­ing or in an­oth­er lan­guage not spo­ken in their homes. By ten to 12 months, how­ev­er, mono­lin­gual ba­bies were no longer de­tect­ing sounds in the sec­ond lan­guage, on­ly in the lan­guage they usu­al­ly heard.

The re­searchers sug­gest­ed that this rep­re­sents a process of "neur­al com­mit­ment," in which the in­fant brain wires it­self to un­der­stand one lan­guage and its sounds.In con­trast, the bilin­gual in­fants fol­lowed a dif­fer­ent de­vel­op­men­tal tra­jec­to­ry. At six to nine months, they did not de­tect dif­fer­ences in pho­net­ic sounds in ei­ther lan­guage, but when they were old­er, ten to 12 months, they were able to dis­crim­i­nate sounds in both."What the study demon­strates is that the vari­abil­i­ty in bilin­gual ba­bies' ex­pe­ri­ence keeps them open," said Dr Pa­tri­cia Kuhl, co-di­rec­tor of the In­sti­tute for Learn­ing and Brain Sci­ences at the Uni­ver­si­ty of Wash­ing­ton and one of the au­thors of the study.The learn­ing of lan­guage, and the ef­fects on the brain of the lan­guage we hear, may be­gin even ear­li­er than six months of age.Janet Werk­er, a pro­fes­sor of psy­chol­o­gy at the Uni­ver­si­ty of British Co­lum­bia, stud­ies how ba­bies per­ceive lan­guage and how that shapes their learn­ing. Even in the womb, she said, ba­bies are ex­posed to the rhythms and sounds of lan­guage, and new­borns have been shown to pre­fer lan­guages rhyth­mi­cal­ly sim­i­lar to the one they've heard dur­ing fe­tal de­vel­op­ment.In one re­cent study, Dr Werk­er and her col­lab­o­ra­tors showed that ba­bies born to bilin­gual moth­ers not on­ly pre­fer both of those lan­guages over oth­ers, but are al­so able to reg­is­ter that the two lan­guages are dif­fer­ent.In ad­di­tion to this abil­i­ty to use rhyth­mic sound to dis­crim­i­nate be­tween lan­guages, Dr Werk­er has stud­ied oth­er strate­gies that in­fants use as they grow, show­ing how their brains use dif­fer­ent kinds of per­cep­tion to learn lan­guages, and al­so to keep them sep­a­rate.

In a study of old­er in­fants shown silent video­tapes of adults speak­ing, four-month-olds could dis­tin­guish dif­fer­ent lan­guages vi­su­al­ly by watch­ing mouth and fa­cial mo­tions and re­spond­ed with in­ter­est when the lan­guage changed.By eight months, though, the mono­lin­gual in­fants were no longer re­spond­ing to the dif­fer­ence in lan­guages in these silent movies, while the bilin­gual in­fants con­tin­ued to be en­gaged.Dr Kuhl calls bilin­gual ba­bies "more cog­ni­tive­ly flex­i­ble" than mono­lin­gual in­fants. Her re­search group is ex­am­in­ing in­fant brains with an even new­er imag­ing de­vice, mag­ne­toen­cephalog­ra­phy, or MEG, which com­bines an MRI scan with a record­ing of mag­net­ic field changes as the brain trans­mits in­for­ma­tion.Pre­vi­ous re­search by her group showed that ex­pos­ing Eng­lish-lan­guage in­fants in Seat­tle to some­one speak­ing to them in Man­darin helped those ba­bies pre­serve the abil­i­ty to dis­crim­i­nate Chi­nese lan­guage sounds, but when the same "dose" of Man­darin was de­liv­ered by a tele­vi­sion pro­gramme or an au­dio­tape, the ba­bies learned noth­ing. (New York Times)


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