Abstract： Poverty of stimulus is a key argument in generative linguistics， claiming that language input doesn’t accord with linguistic competence they ultimately develop， and that language acquisition has to rely on innate language knowledge. A child can learn his mother tongue easily， though he may be exposed to the language limitedly. However， the development of wolf child's language ability isn't in line with Chomsky's poverty of stimulus to a certain degree. Here I shall present my understanding on why this phenomenon occurs and factors that influence children's language acquisition.

Key Words： poverty of stimulus; wolf child; language acquisition.

1. Poverty of Stimulus

Chomsky first used the term in 1980， which means poverty of language stimulus. But children are exposed to L1 everyday， how could language input be poor？ In fact， it’s just a superficial phenomenon--Chomsky found that language input and output were skewed， and then he put forward Innateness Hypothesis. Meanwhile， Chomsky realized children could learn L1 through very limited language stimulus. In general， a child without systematic classroom learning can reach the level of adults. So， why do the asymmetry of language input and output exist？ If language needs learning， how long will it take children to speak as fluently as adults do？ But the asymmetry of language input and output does exist， so the only reasonable hypothesis is that there's a language acquisition mechanism in human brain.

2. The Development of Wolf Child's Language Ability

Two wolf children were found in Indian in 1919. One was eight， and the other was about 2. They were taken back to human world and were named Kamala and Amara. Amara can pronounce very simple syllables to express hunger or thirst， but he died in the eleventh month after he came back. Kamala could only pronounce two simple words after years’ efforts. It's a pity that Kamala couldn’t speak as fluently as others do until his death， and had the intelligence of three-year-olds. Thus here comes a question： According to Chomsky's poverty of stimulus， there exists universal grammar in wolf children's brain， but why their language ability couldn't improve after years of efforts？ And what's the cause for stabilization of their language ability？

3. Critical Period Hypothesis and Its Enlightenment on Language Acquisition

Critical period is a specific phase when learners can master a language without exterior intervention. Lenneberg proposes that the process of language acquisition is determined by biological factors. According to Krashen's language input hypothesis， language acquisition is mainly a subconscious act. However， in their childhood， wolf children lived with wolf and all they could hear is wolf's words. This explains why Chomsky's poverty of stimulus didn't work for wolf children. So we should make full use of critical period of language acquisition and increase high-quality language input within this period. Only in this way can we get best results in language acquisition.

4. Language Acquisition--A Combination of Stimulus-response and Language Innateness

Language acquisition is an important part of psycholinguistics， which is not only the simple stimulus-response or language innateness， but the combination of the two.

4.1 Stimulus-response Hypothesis ﹠Innateness Hypothesis

That gorillas can learn human language is an important fact strongly favored by behaviorists. \"Language sense\" is often mentioned in language learning， which can be obtained easily. Such psychology intuition exists even for L2 learners. However， it can't be explained by stimulus-response hypothesis. Oppositely， it can prove that there exists universal grammar in human language， which is inheren shared by human.

Innateness hypothesis proposes language evidence is a necessary condition of language acquisition. It refers to corpus learners can get in touch with. If children can't get negative evidence in their learning， they'll have to rely on universal grammar to obtain \"1 consciousness\". However， non-innateness theorists proved that language input in children's early learning is not poor， and that corpus they get in touch with is not completely right. This is the contradiction of innateness hypothesis.

4.2 Language Acquisition： the Combination of Stimulus-response and Language Innateness

From those above， it is clearly they both can't fully explain all problems in language acquisition. The example of 'wolf child' story contradicts Chomsky's innateness hypothesis and proves environmental stimulus and effect are also of great importance. According to innateness hypothesis， universal grammar also exists in wolf child's brain. But without external stimulus， they can't speak. They can only pronounce simple syllables after continuous input and stimulus. Therefore， language acquisition needs the combination of the two. At the primary learning stage， people need environmental stimulus-response. With internal information storage increasing， cerebral internal setup， association and reasoning work a lot.

5. Summary

From those above， it is clear that language acquisition is a rather complex process influenced by many factors， such as innate quality， postnatal environment， etc. None of them can separately work efficiently. Therefore， only by making full use of these factors， can they be better applied to and guide children's language acquisition.

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