The critical period hypothesis in language acquisition

When learning about the process of language acquisition, two approaches are normally distinguished: The behavioural approach and the nativist approach.

In this article we are going to explain the different approaches paying special attention to  the Critical Period Hypothesis.

– The Behaviouristic Approach maintains that children acquire the language through environmental components: learner imitation, practice, feedback on progress and habit formation.

-The Nativist Approach, which was raised by Noam Chomsky, holds that children are biologically programmed for language, in the same way as they are for functions, for instance, figuring out how to walk. Their inherent capacity enables them to become competent language users regardless of their learning environment. Chomsky named this innate knowledge the language acquisition device (LAD).

Noam Chomsky
  1. What is the Critical Period Hypothesis?

The Critical Period Hypothesis is the ability to acquire language biologically linked to  age. This hypothesis claims that there is a period of growth, from early childhood to adolescence, in which full native competence is possible when learning  a language.

Derived from biology, this concept was presented by Penfield and Roberts in 1959 and refined by Lenneberg in 1967. Lenneberg contended that the LAD needed to take place between age two and puberty: a period he believed to correspond with the lateralisation process of the brain. The lateralisation process of the brain is it a complex and ongoing procedure that refers to the tendency for some cognitive processes to be more dominant in one hemisphere than the other. According to Lenneberg this idea was concerned with the implicit “automatic acquisition” in immersion contexts and does not stop the possibility of learning a foreign language after adolescence, but with a lot more effort and typically less achievement. Lenneberg likewise expressed that the development of language is a result of brain maturation: equipotential hemispheres at birth, language gradually becoming lateralized in the left hemisphere.

2.  Evidence of the Existence of the Critical Period.

In October 1970, a girl nicknamed Genie was found by social workers in Los Angeles, California. Genie had been locked in a dark room alone and tied up to a chair. She had never socialized nor spoken to anyone. Her development was extremely delayed due to the abuse she experienced during her life. In fact, when the social workers found her they thought she was between five or six years old even though she was thirteen. For this reason, she could not walk correctly, eat properly, or speak in any language.

Genie was accepted into an hospital in where specialists started to try to teach her how to speak. Despite learning about one hundred individual words, in her life she was never able to use grammar correctly or put the words together to make meaningful sentences.  During her period in this hospital, some tests were done on her. These tests confirmed that she was not mentally ill and that her difficulties were created because she was mistreated since her birth. The final tests on Genie’s brain showed that the side which records language, the left side, was not working properly. Her brain looked like the ones of children whose left hemispheres had been removed since her left hemisphere had been never used until they found her, so according to the Critical Period Hypothesis, she lost her ability to learn any language.

Nowadays Genie is living in an adult foster care home in California and is 55 years old.


As a conclusion, due to the Critical Period Hypothesis, Genie mostly uses the right hemisphere of her brain because of the setback and inability to use the left hemisphere of her brain. Nevertheless, the existence of this case does not mean that this hypothesis can be held as a fact. Here it has been proved that in order to learn a language, the maturation of the brain is important but also environmental factors are important since this concrete girl did not learn how to speak because her environmental conditions were not the correct ones, so her brain could not develop properly.

by Alba Malagon Diaz


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