The Critical Period Hypothesis examines questions such as: “Would I have had a better understanding of language X had I started learning it earlier on?”, or “Would a child reared in the wild be able to develop a linguistic system?”.

The Critical Period Hypothesis basically sustains that Language Acquisition would be at its best until the age of 12. After this time barrier, not only would learning a language be more challenging, but it would also be not as fruitful as one would like and never would an individual after the age of 12 grasp a language as perfectly as a native speaker.

Not to put things too pessimistically, it all boils down to simple biology. The capacity to acquire language is biologically determined, it is an integral part of a general cognitive ability. Sustaining this, it would be logical to deduce that an individual may be able to learn a language as long as there is a sort of “readiness” in the brain to receive this language.

If language acquisition is a biological utility linked directly to the left hemisphere of the brain, where linguistic functions reside, one would expect the brain to have allocated a special place to receive this utility. In the case of feral children, those who did not get the chance to live in a proper linguistic environment, this place in the brain is not developed because the brain had not been stimulated to create it.

Another example on this point is left hemisphere damage. Should the left hemisphere be subject to damage, in adults it would take it five months to recover. If not, the individual’s linguistic abilities would perish. This recovery takes a longer time in children, and it is generally full. In some extreme cases, when the child is very young, sever damage and even removal of large parts of the left hemisphere do not affect language acquisition.

It’s all about plasticity. When a child’s brain grows, and his linguistic abilities grow in parallel lines with it, language acquisition is a breeze. That moment in time gone, the brain reaching its lateralization without a matching linguistic growth,therefore losing its plasticity, language acquisition would become difficult.

Cases of feral children trying to compensate for their linguistic losses are cited from this link.

” The first case was a deaf mute child named Isabelle, who was found at the age of six and half. She spent alone in a darkened room before being found, but she succeeded in her language learning because she was at the age of six and half. Brown (1958: 192, cited in Aitchison 1989:85) recorded:

Isabelle passed through the usual stage of linguistic development at a greatly accelerated rate. She covered in two years the learning that ordinarily occupies six years. By the age of eight and one half Isabelle was not easily distinguishable from ordinary children of her age.
It is reasonable to consider that she was able to acquire her language because she started learning before the critical period came to an end.

The second case was Genie, who was found at the age of about fourteen (Curtiss, Fromkin, Krashen, Rigler, and Rigler 1974). Because she started learning a language after the critical period, her progress was slower than other children. For example, her two-word stage, at which every child goes though uttering two words at a time like ‘Want milk’ and ‘Mummy play,’ lasted much longer. Genie used this type of primitive form and its negation such as ‘No want milk’ for a longer period. Her ability to learn vocabulary was superior to other children. However, her grammatical development was much slower and unsuccessful, because her critical period had passed already. Since she started learning a language after she was already pubescent, Genie had to take quite a long time to acquire a language.

The third case was Chelsea, who started to learn language in her early thirties (Curtiss 1988). She showed poor grammatical ability like Genie, but her vocabulary was better. It was recorded that her syntax created sentences such as ‘the woman is bus the going’ and ‘banana the eat.’

All these cases of children reared in isolated environments reveal the difficulties of learning a language after the critical period”


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