【Abstract】This paper reviews the emergence and development about “the critical period hypothesis” of second language acquisition（hereinafter called “the hypothesis”） . The author gives the corresponding suggestions according to the hypothesis.

【Key words】Second Language Acquisition; the Critical Period Hypothesis; target language

【作者簡介】白航凡（1995.01-），女，漢族，河北定州人，河北大學(xué)外國語學(xué)院，碩士研究生在讀，研究方向：外國語言學(xué)及應(yīng)用語言學(xué)專業(yè)。

Ⅰ. Introduction

The critical period hypothesis of language acquisition was proposed by Lenneberg （1967） ， which has been widely recognized in the field of first language acquisition. However， its controversy in the field of second language（hereinafter called L2） acquisition is far from over.

Ⅱ. The Critical Period Hypothesis of the first language acquisition

The Critical Period Hypothesis believes that there is a period that is crucial to language acquisition. But domestic and foreign scholars have different views on the specific time of the critical period. Lenneberg （1967） believed that the critical period of language learning was from the age of 2 to adolescence. Krashen （1973） believes that humans peak period of language development is at 5 years old.

Ⅲ. The Critical Period Hypothesis of the second language acquisition

Some theoretical results in the field of the first language acquisition are often applied to the field of the L2 acquisition. Many linguists have used different experimental methods to prove their views.

The viewpoint of the proponents

The proponents mainly confirm the rationality of their views from three aspects： Firstly， the effect in learning L2 is more dominant in children than adults; secondly， the factor of age is important to affect L2 learning; Thirdly， a few of the adult L2 learners are able to reach the level of their own native speakers.

Through one year study， Snow&Hoefnagel-Hohle （1982） found that the initial advantages of adult learners cannot be retained for a long time. By studying L2 learners aged 4 to 42， Thompson （1991） found that learning age is the most powerful factor predicting the target language level. Through further investigations of the immigrants accent， Patkowsky （1994） concluded that 15 years of age is the end of the critical period .

The viewpoint of the opponents

The opponents put forward three reasons to argue that “there is no critical period in L2 acquisition.” Firstly， the influence of non-biological factors on the L2 acquisition effect cannot be ignored. Secondly， some experiments showed that older L2 learners can also successfully learned. Thirdly， learners of different ages have different advantages in L2 acquisition.

Flege （1999） found that there is a linear relationship between the L2 learners age and the target language pronunciation ， but there is no obvious turning point at any stages of learners age. Birdsong & Molis （2001） concluded that L2 learners after the end of puberty can reach the same level as the target language native.

Ⅳ. The problems and prospects of the critical period research in the field of second language acquisition

The controversy about the question of whether the L2 acquisition has a critical period mainly focuses on the following four aspects： first， whether there is a critical period. Second， What is the reason for the existence of the period. Third， when does the critical period start and end （Jiang Meng， Deng Xiaoyan， Ou Pingya， 2010）. Fourth， whether there is a unified critical period. This auther argues that before the study， a unified conceptual standard of the definition of “the critical period of L2 acquisition” must be formulated.

Ⅴ. Conclusion

There is no uniform standard for the learners target language level， so the hypothesis is difficult to be proved. In addition， the factors affecting second language acquisition are numerous and complex. Therefore， in the course of the experiment， we should pay attention to the control of related variables and minimize the impact of unrelated variables to increase the credibility of the experiment.

References：

[1]Birdsong， D. & M. Molis.In the Evidence for Maturational Constraints in Second Language Acquisition[J]. Journal of Memory and Language，2001（44）：235-249.

[2]Flege. J. E. Age of Learning and Second Language Speech. In? D.Birdsong（ed.）. Second Language Acquisition and the Critical Period Hypothesis[C]. NJ： Lawrence Erlbaum Associates，1999：100-32.

[3]姜孟，鄧小燕，歐平亞.第二語言習(xí)得關(guān)鍵期假說五十年之爭[J].當(dāng)代外語研究，2010（9）：10-16.