Neuroscientists have long observed that learning a language presents a different set of opportunities and challenges for adults and children。

Adults easily grasp the vocabulary needed to navigate a grocery store or order food in a restaurant, but children have an innate ability to pick up on subtle nuances of language that often elude adults。

For example, within months of living in a foreign country, a young child may speak a second language like a native speaker。

Experts believe that brain structure plays an important role in this “sensitive period” for learning language, which is believed to end around adolescence。

The young brain is equipped with neural circuits that can analyze sounds and build a coherent set of rules for constructing words and sentences out of those sounds。

Once these language structures are established, it’s difficult to build another one for a new language。

長期以來，神經(jīng)學(xué)家一直認(rèn)為語言的學(xué)習(xí)對成年人和孩子來說有著不同的機(jī)遇與挑戰(zhàn)。

成年人很容易地掌握雜貨店或餐館必備詞匯，孩子就有與生俱來能力，辨別語言中細(xì)微的差別，而這些差別經(jīng)常會把成年人難住。

比方說，孩子只要在國外生活幾個(gè)月，就可以像外國人一樣說外語。

一些專家認(rèn)為大腦結(jié)構(gòu)會影響人們語言學(xué)習(xí)的敏感期，而敏感期止于青春期。

孩子的大腦含有神經(jīng)回路，能夠分析聲音，建立起一套連貫的規(guī)則，從而利用這些聲音組詞造句。

這些語言結(jié)構(gòu)建立完成，大腦就很難形成新的結(jié)構(gòu)，學(xué)習(xí)新一門語言。

In a new study, a team of neuroscientists and psychologists from Massachusetts Institute of Technology (MIT) discovered another factor that contributes to adults’ language difficulties: When learning certain elements of language, adults’ more highly developed cognitive skills actually get in the way。

The researchers discovered that the harder adults tried to learn an artificial language, the worse they were at deciphering the language’s morphology —the structure and deployment of linguistic units such as root words, suffixes, and prefixes。

“We found that effort helps you in most situations, for things like figuring out what the units of language that you need to know are, and basic ordering of elements. But when trying to learn morphology, at least in this artificial language we created, it’s actually worse when you try,” said Amy Flynn a postdoc at MIT’s McGovern Institute for Brain Research。

Finn and colleagues from the University of California at Santa Barbara, Stanford University, and the University of British Columbia describe their findings in journalPLOS ONE。

Linguists have known for decades that children are skilled at absorbing certain tricky elements of language, such as irregular past participles (examples of which, in English, include “gone” and “been”) or complicated verb tenses like the subjunctive。

“Children will ultimately perform better than adults in terms of their command of the grammar and the structural components of language —some of the more idiosyncratic, difficult-to-articulate aspects of language that even most native speakers don’t have conscious awareness of,” Finn says。

In 1990, linguist Elissa Newport hypothesized that adults have trouble learning those nuances because they try to analyze too much information at once. Adults have a much more highly developed prefrontal cortex than children, and they tend to throw all of that brainpower at learning a second language。

This high-powered processing may actually interfere with certain elements of learning language。

“It’s an idea that’s been around for a long time, but there hasn’t been any data that experimentally show that it’s true,” Finn says。

Finn and her colleagues designed an experiment to test whether exerting more effort would help or hinder success。

在一項(xiàng)研究中，由來自麻省理工學(xué)院(MIT)神經(jīng)學(xué)家及心理學(xué)家組成的研究團(tuán)隊(duì)發(fā)現(xiàn)另一種因素，可以解釋成年人學(xué)習(xí)語言的難點(diǎn)：在學(xué)習(xí)語言的某一方面時(shí)，成年人高度發(fā)達(dá)的認(rèn)知技能實(shí)際上阻礙了語言的學(xué)習(xí)。

研究人員發(fā)現(xiàn)，成年人在學(xué)習(xí)人造語言的過程中越努力，那么他們在學(xué)習(xí)語言形態(tài)學(xué)方面表現(xiàn)就越糟糕。(形態(tài)學(xué)指的是詞根、后綴及前綴等語言單位的結(jié)構(gòu)及組合。)

“研究發(fā)現(xiàn)，多數(shù)情況下，努力有所作用，比如，你想要解出你需要知道的是那種語言單位及基礎(chǔ)的成分順序安排。但是，當(dāng)你想要學(xué)習(xí)形態(tài)學(xué)的時(shí)候，學(xué)習(xí)我們自己創(chuàng)造的語言時(shí)，越努力，效果越差。”麻省理工學(xué)院麥戈文人腦研究所的博士后艾米·弗林(Amy Flynn)表示。

來自加州圣巴巴拉大學(xué)、斯坦福大學(xué)及英屬哥倫比亞大學(xué)的芬恩(Finn)及同事在《公共科學(xué)圖書館·綜合》雜志上發(fā)表了他們的研究成果。

幾十年來，語言學(xué)家都知道孩子善于消化吸收語言學(xué)習(xí)中的難點(diǎn)問題，像是不規(guī)則過去分詞(英語中的例子，比如“gone”和“been”)或是虛擬語氣中復(fù)雜的動(dòng)詞時(shí)態(tài)。

“對于語法及句式結(jié)構(gòu)，孩子總會比成年人掌握地更好，比如，即便是說母語的人大[微博]多也沒有意識到的一些比較特殊、發(fā)音困難的問題等。”芬恩說。

1990年，語言學(xué)家愛麗莎·紐波特(Elissa Newport)提出一個(gè)假設(shè)，成年人理解這類細(xì)微差別有困難是因?yàn)樗麄冊噲D同時(shí)分析過量的信息。成年人的前額皮質(zhì)比起孩子，更加高度發(fā)達(dá)，他們往往會絞盡腦汁去學(xué)習(xí)第二門語言。

事實(shí)上，這個(gè)高強(qiáng)度的學(xué)習(xí)過程也許會干擾某些語言學(xué)習(xí)因素。

“這個(gè)想法已存在多時(shí)，但是目前為止，沒有任何實(shí)驗(yàn)數(shù)據(jù)證明它的正確性。”芬恩說。

芬恩及同事設(shè)計(jì)了一個(gè)實(shí)驗(yàn)，測試付出更多的心力是否有助于或有礙于語言學(xué)習(xí)。

The Study

研究過程

First, they created nine nonsense words, each with two syllables. Each word fell into one of three categories (A, B, and C)， defined by the order of consonant and vowel sounds。

Study subjects listened to the artificial language for about 10 minutes. One group of subjects was told not to overanalyze what they heard, but not to tune it out either。

To help them not overthink the language, they were given the option of completing a puzzle or coloring while they listened. The other group was told to try to identify the words they were hearing。

Each group heard the same recording, which was a series of three-word sequences —first a word from category A, then one from category B, then category C —with no pauses between words。

Previous studies have shown that adults, babies, and even monkeys can parse this kind of information into word units, a task known as word segmentation。

首先，他們創(chuàng)造了九個(gè)毫無意義的詞，每個(gè)詞兩個(gè)音節(jié)。再根據(jù)輔音及原因的排列，將這些詞分為三類(A、B及C類)。

研究對象聽這些人造語言大約10分鐘。其中一組被告知不要過度分析他們聽到的內(nèi)容，也不要置若罔聞。

為了不讓他們過度分析，他們可以選擇在聽的過程中完成拼圖或給圖上色。另外一組被告知要盡量辨析他們聽到的內(nèi)容。

每個(gè)小組聽的都是同樣的內(nèi)容，三個(gè)單詞為一個(gè)單位，第一個(gè)為A類詞，第二個(gè)B類，接著C類，詞與詞中間沒有停頓，

既往研究顯示成年人、孩子，甚至是猴子都能理解這類單詞組信息，亦被稱為“詞切分”。

Subjects from both groups were successful at word segmentation, although the group that tried harder performed a little better. Both groups also performed well in a task called word ordering, which required subjects to choose between a correct word sequence (ABC) and an incorrect sequence (such as ACB) of words they had previously heard。

The final test measured skill in identifying the language’s morphology。

The researchers played a three-word sequence that included a word the subjects had not heard before, but which fit into one of the three categories。

When asked to judge whether this new word was in the correct location, the subjects who had been asked to pay closer attention to the original word stream performed much worse than those who had listened more passively。

The findings support a theory of language acquisition that suggests that some parts of language are learned through procedural memory, while others are learned through declarative memory。

Under this theory, declarative memory, which stores knowledge and facts, would be more useful for learning vocabulary and certain rules of grammar。

兩組實(shí)驗(yàn)對象都能成功地完成詞切分，雖然認(rèn)真分析的那組表現(xiàn)更好一點(diǎn)。同樣地，在詞匯順序排列的任務(wù)中，兩組也都完成得很好。第二個(gè)任務(wù)要求實(shí)驗(yàn)對象在聽過的正確次序(ABC)與錯(cuò)誤詞序(ACB)中作出選擇。

最終測試考量他們在辨別語言形態(tài)方面的技能。

研究人員播放一連串三詞組和，其中包括他們沒有聽過的詞序，但也符合分類要求。

當(dāng)為要求對新詞詞序作出判斷時(shí)，認(rèn)真分析原詞語流的那組實(shí)驗(yàn)對象表現(xiàn)比消極地聽的那組差得多。

研究結(jié)果與語言習(xí)得的一個(gè)理論相符，那就是，語言的某些部分是通過程序記憶學(xué)習(xí)來的，然而其他的一些是由陳述性記憶習(xí)得的。

在該理論體系下，陳述性記憶，用于儲存知識與事實(shí)，這種記憶在詞匯與某些語法規(guī)則的學(xué)習(xí)中作用更明顯。

Procedural memory, which guides tasks we perform without conscious awareness of how we learned them, would be more useful for learning subtle rules related to language morphology。

“It’s likely to be the procedural memory system that’s really important for learning these difficult morphological aspects of language。

“In fact, when you use the declarative memory system, it doesn’t help you, it harms you,” Finn says。

Still unresolved is the question of whether adults can overcome this language-learning obstacle. Finn says she does not have a good answer yet but she is now testing the effects of “turning off” the adult prefrontal cortex using a technique called transcranial magnetic stimulation。

Other interventions she plans to study include distracting the prefrontal cortex by forcing it to perform other tasks while language is heard, and treating subjects with drugs that impair activity in that brain region。

程序性記憶，指導(dǎo)我們在不了解學(xué)習(xí)方式的情況下完成任務(wù)，這種記憶在語言形態(tài)相關(guān)的微妙規(guī)則學(xué)習(xí)中作用更明顯。

“在較有難度的語言形態(tài)學(xué)方面的學(xué)習(xí)中，程序性以及系統(tǒng)可能發(fā)揮著更大的作用。”

“事實(shí)上，使用陳述性記憶體系，并不起作用，反而是幫倒忙。”芬恩說。

令人未解的仍是成年人是否能夠克服語言學(xué)習(xí)的障礙。芬恩說她也沒有一個(gè)合理的答案，但是現(xiàn)在她正使用叫做經(jīng)顱磁刺激的技術(shù)，測試“關(guān)閉”成年人前額皮質(zhì)的作用。

她還計(jì)劃研究其他方面的干擾，比如在聽的過程中，通過強(qiáng)制性地完成任務(wù)，干擾前額皮質(zhì)，使用藥物影響大腦特定區(qū)域的活動(dòng)等。