Secondly, a research paper from Grimshaw demonstrates the status how a deaf child learned language。 This Mexican boy called E。M。 was deaf owing to congenital disease, communicating with his parents in virtue of sign languages。 It was not until 15 that he was installed a hearing aid to help him hear other talk。 Thereafter E。M。 started picking up Spanish at home。 Grimshaw et al tested him from aspects of language production and language comprehension。 It turned out that his pronunciation was still in a dilemma after his using a hearing aid for 34 months。 When asked to describe a familiar cartoon card, he could only utter one word – Gat (cat) and write down several uncomplicated words。 48 months later, his communication mainly relied on sign language as before (Grimshaw 237)。 All these signals suggested E。M。 got tiny enhancement of language acquisition over a two-year study。 In a word, Grimshaw’s investigation showed the reason that children without hearing met difficulty in language learning past puberty was more likely to be the loss of the critical period, not cognitive or emotional deficiencies。 This research further supported CPH Lenneberg raised。

Thirdly, Johnson and his partners studied the English grammar mastery of a number of immigrants whose first languages were Korean or Chinese。 The age of these testees reaching the United States varied from 3 years old to 39 years old。 In the experiment, testees were pided into 2 groups。 Members of the first group arrived at the United States before 15 years old。 The other group comprised participants who landed there after 17 years old。 Both of them had lived in the United States for averagely 9 years。 The only task for them was to judge whether a couple of oral sentences were compliant with syntax。 It was found that the earlier they got there, the better they grasped English grammar。 People who came there within 3-7 years old could speak as fluently as native Americans and test scores began to decline after 8 years old。 Overall, the later they learned the worse the mastered and the downtrend was gradually gentle (Johnson 21)。 Johnson’s survey elucidated there was a crucial age in the English grammar study。 Learners who initiated receiving English education ahead of 8 years old could score best。 Once passing certain crucial age, learners’ effectiveness of language acquisition would be relatively poor。 

In respect of the overall advantage on child second language acquisition, Littlewood gave the following four explanations。 First, children generally have more favorable learning conditions and could always contact languages in a longer period of time, which would attract native speakers of the target language, other children and elders’ close attention。 Additionally, the language that children approach is probably less complex (i。e。 simple language code or compassionate speech)。 Such type of input is prone to comprehend and handle。 Moreover, children barely hold negative attitudes toward other speech community or realize other relevant factors, causing low “social-emotional barriers”。 Last but not least, adults are apt to consciously cerebrate and analyze learning experiences, which potentially obstructs natural processing mechanism’s function of internalizing new language。 Elder learners are too dependent on “learning” while children are willing to “acquire” unaffectedly (Littlewood。W, 1984)    文献综述

On the other side, opposers of CPH cannot completely overthrow it with sufficient evidences or collected samples by now。 Their tested samples were too excellent in second language learning, whose second language level were very close to or already reached native speakers’, not universal enough。 Plus the linguistic phenomenon they studied was confined to a small sample of language, not representative enough (Harley and Wang 1997)。

In the research of language acquisition, objectors against CPH commonly don’t repudiate the statement that it is easier for children to achieve success in language acquisition, whose learning speed may be slower than adults at first but they would be the winner at last (Larsen and Long 1991)。  关键期假说实证研究(3):http://www.youerw.com/yingyu/lunwen_85070.html