Abstract： Some scholars hold different ideas to the Critical Period Hypothesis， and they developed the Sensitive Period Hypothesis. This article is to analyze the theory and the studies related to it.

Key words： Critical Period Hypothesis， Second Language Acquisition， Age

1 The introduction of Sensitive Period Hypothesis

Owing to the disagreement on the Critical Period Hypothesis， many scholars turned to more research for evidence. And a much more neutral hypothesis—the Sensitive Period Hypothesis （Oyama， 1976） appeared. It was supported by M. Patkowski and F. Carroll with their investigations. This notion also derives from Lenneberg’s（1967） hypothesis concerning the existence of a critical period for the acquisition of the first language extending from about two years old to the close of puberty.

2 The distinction between CPH and SPH

Lamendella introduces the term SPH and it is now often interchangeably used with Critical Period， which refers to the notion that the age limitation is absolute. In theory， first language acquisition is not possible past the critical point. The term Critical Period also refers to the fact that the age limitation is not absolute. So， the distinction between the CPH and the Critical Period Hypothesis is whether acquisition is possible only within the definite span of age or easier within the period. Seliger's proposal is that there may be multiple critical or sensitive periods for different aspects of language. The period during which a native accent is easily acquirable appears to end earlier than the period governing the acquisition of a native grammar.

3. Neurological basis

F. Carroll provided neurological basis for the Sensitive Period Hypothesis. He carried out a test whose results implied that early exposure to second language， however little it was or even the second language was not used， was of great significance to successful achievement of second language acquisition. Early exposure can give rise to qualitatively different attainment of language acquisition even though the later language learning occurs in formal classroom environment. Carroll held the view that early exposure to second language appeared to stimulate the nerve system， thus， promoting later language acquisition.

4 Conclusion

According to the Sensitive Period Hypothesis， there seems to be an optimal age in second language acquisition. But this age is still a debating issue， and it needs further exploration in near future. What can be certain is that the view of “the younger， the better” is not convincing in the field of second language acquisition. In 1985， the Chinese National Committee of Education did an investigation into English teaching in middle schools， and the results show that adults， despite their neurological shortcomings， can also learn a second language well through individual efforts and with proper training. To learn a foreign language too early would interfere in the development of logical thinking ability. Besides age， the important factors that determine whether a learner can have a good command of a foreign language lie in the efforts that the learners make， qualified teachers and language environment.

Bibliography

[1] Larsen-Freeman， Diane amp; Michael H. Long. An Introduction to Second Language Acquisition Research. Beijing： Foreign Language Teaching and Research Press， 2000.

[2] Ellis， Rod. Second Language Acquisition. Oxford：Oxford University Press，1997.

[3] Selinker， Larry. Second Language Acquisition—An Introductory Course. London：Lawernce Erlbum Associations， 2001.