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Critical period hypothesis in language acquisition


In this research paper I try to state paradigms that are in support of the existence of Critical Period Hypothesis like the brains of children that are craving for input which they just absorb, feral children that show no signs of hope for the acquisition of language since they were deprived of language during their critical period and the lateralization of the brain which seems to coincide with this period of language sensitivity. Furthermore, evidence of the resurrection of this critical period will be stated but which at the end confirm that nothing can substitute the years between early childhood and puberty.


Throughout the centuries, an extremely controversial issue has been lingering among scientific, linguistic circles; millions of attempts have been carried out to shape and specify why children acquire language in a -seemingly- easy way. To be more precise myself, the huge topic which millions of books and scholarly papers have been dedicated to, is the Critical Period Hypothesis. Extended argumentation exists over this theory which appears to provide us with satisfactory evidence as to why children seem to acquire their first language in an extremely different way from adults that struggle to learn a second language. Critical Period Hypothesis also seems to have an account for second language acquisition; with the age for being a limit. It shares its benefits with children who have not reached their puberty, that is their thirteen-more or less- years of age. Despite some evidential elements that go against this particular theory, Critical Period Hypothesis seems to be the factor that is always present as far as language acquisition is concerned. There has to be something special about the way we learn our mother tongue and the path we follow to catch up with as second language while being children; the shared characteristic is age and this can by no means be random.

What is the Critical Period Hypothesis

The Critical Period Hypothesis had been first introduced by Lenneberg and states that during our early years and till our puberty we are programmed to take up linguistic data and manage to build up our language system in a manner that appears to be unique. Our capacity for learning is at its extreme and our minds have no barrier; they simply receive linguistic data and progressively structure language from its rudimental parts to the more complex and difficult elements. Once that particular period ceases, this priviledge somehow shrivels, gradually stops its function and our receptivity to language appears to be at a descending level.

Critical Period Hypothesis and the Brain

Critical Period Hypothesis is highly associated or even achieves a perfect match with the mind of children. During their first years of life, children have a blank brain that is ready to accept knowledge without filtering it; that is, its receptivity is at its peak.

The advantageous point lies in the act that children's raw and empty brain allows them access the information they take till their last bit, their last aspect. Their limited knowledge about how language is formed and organized and the qualitatively poor linguistic data they are exposed to may appear to be a severe drawback but surprisingly it transforms itself and is turned to be deeply beneficial. It is incomparably easier to look up in their small storage, combine and connect the new input with the previously received data, a task that for an adult is far more complex and a lot harder. Children start with a limited store and progressively develop it, adding more and more elements and moving slowly but successfully from the simple to the more advanced level of competence. It is evident that when she or he lacks a linguistic background that already consists of a fully develops language system, the child can stay focused on one ask at a time and then move on building connections between the most recent and the older characteristics, until eventually to become fully equipped with an autonomous linguistic system.

Moving to the next stage, while the child grows, its cognitive abilities become more and more sophisticated so it is more demanding for him or her to view language acquisition as a process that just happens and is innate. They seem to, as they develop their linguistic skills, not to be in need anymore of the help of their blank brain, so the light slowly fades away and a whole new process for language learning is set in function.

This whole new way of learning is considered to have its application also on adults and, as David Birdsong puts it, "[w]hereas the attainment of full linguistic competence is the birthright of all normal children, adults vary widely in their ultimate level of attainment and linguistic competence" (p.1). The above statement can be probably enlisted in the most strong evidence for the existence of Critical Period Hypothesis, since adults find it quite intriguing just to receive unfiltered linguistic information and accept them without question. Their already existent language system and its excessive use form a burden that not only blocks the free entrance, access and establishment of linguistic information but also confuses the learners that are trapped in a continuous stage of comparing what they already know with what they are learning now.

Despite the fact that adults have to face the drawbacks of the passing of their critical period, their knowledge of language apparently supplies them with some advantages too. According to Krashen et al (as cited by David Singleton), "adults proceed through early stages of syntactic and morphological development faster than children" (p.5), a notice that can possibly be extracted from the fact that adults' know-how of language organisation provides them with assistance in order to move on more quickly to the next stage of language learning, when difficulties with linguistic acquirement seem to occur.

Critical Period Hypothesis and its extension

The possibility of the conservation of our critical period could be the ideal scenario for language learning. Unfortunately, this is not the case; at least not to its whole. Besides the obvious difficulties -like age of course! We cannot possibly move back ad fourth between two and thirteen- there is evidence that, providing that it is given food, Critical Period can be kept alive, at least to some level.

The key to that is simply never let our brain without practicing; we have to keep it alive somehow and always supply it with tasks that will demand continuous work, thinking and learning process, a state that seems to coincide with David Birdsong's view that "learning is a matter of progressively accumulating and strengthening input-output associations" (p.7). If we keep practicing our cognitive abilities, they will not atrophy, they are just in need of stimuli in order to have something to work on.

It is convincing enough the fact that people who have a passion for language learning, or learning in general, find it easier to cope with new data and seem to adapt with apparent ease to the new linguistic environment they are exposed. These people face as a less demanding task the conformity to a completely different set of rules and functions of a freshly introduced grammatical system and the common ground of them is that they never stopped learning, the process of exercising their minds never ceased. As Bever successfully states (as cited by David Birdsong), "continuous acquisition can stave off the independence of the systems, and therefore delay the apparent critical period" (p.7), something that reinforces the view of continuous learning as a crucial and fundamental parameter for the preservation of the function of critical period.

Even in its extended model, the Critical Period Hypothesis is strengthened, since children are not faced with the absolute need to continuously feed their minds; they acquire language in such a natural manner that could even be given the characterization o instinctive. Adult learners that benefit from the light of the late critical period, manage to do so after extreme effort and never ending process of exercising their minds, a need that is by no means met by children.

Lateralization and the Critical Period Hypothesis

A strong connection that can most probably not set under question exists between the lateralization of the brain and he Critical Period Hypothesis. The mind at its primary stage is viewed as an entity, with no distinction between the right and the left hemisphere; it appears to be working as a whole, as an autonomous organ that has not yet distributed language to separate parts of the brain. This organization of language in the brain is widely known as lateralization.

"[T]he hemispheres are not specializes for cognitive functioning at birth but begin to become so in the early years" (p.1), a notion developed by Molfese and Segalowitz which allows us to create a bond between that period and the critical period for language learning. During this period our mind is highly flexible and has not differentiated its two distinct components yet, nor has it distributed the several tasks to the separate parts of the brain. Information move freely through the brain and it s processed as a whole; they are not broken into pieces and sent to the domain that is in charge for each one of them, a characteristic that appears to schematize in the best way how children acquire their first language. Language for the young learners is presented as an unbreakable system which they gradually build, starting from its rudiments ad moving towards its special qualities.

Both hemispheres have the same potential during the primary stages of mind development but as time passes and the brain matures, they take the functions each one is responsible of. This quality of the brain as an "equipotential model" (Molfese, Segalowitz p.1) can be clearly demonstrated in cases of brain damage during childhood. There are innumerable cases of children that had damaged severely parts of their brain with little or no consequences in their language acquisition process. It is quite surprising that, having the left or right hemisphere injured, language functions where re-lateralized to the other hemisphere, depending on the case, which took up the functions that would normally be operated by the injured hemisphere. This process, taking place during the critical period, left no trace of linguistic or other cognitive impairment.

The Case of Feral Children

In support of the Critical Period Hypothesis are the cases of feral children, cases that provide striking evidence that the age actor plays a crucial role in the acquisition of language. Children that have been deprived of linguistic data till their puberty years are unable to develop any complete and automatic language system. The distinction between first and second language is unnecessary to be made, since these children could not even master their mother tongue; a second language learning task would be simply impossible.

Throughout the centuries there have been many cases of children that were either abandoned and raised by animals or kept in isolation by their mentally disordered parents with limited or zero human contact. When discovered, they could only produce limited clusters of sounds that were totally random and under no circumstances rule-governed, they could moan or groan or repeat short utterances that were being said to them in the form of commands, that is they were able only to say comprehensible things only through mimicry; they could not assign meaning or acknowledge the possibilities and alternatives of language production. As Katharina Dellbrugge supports, there exists a time in our lives when we are programmed to learn and ready to acquire our first language, a statement that is based on continuous observation of everyday life(p.4), something that is reinforced by the data that are presented to us through encounter with such cases. What attracts attention is the fact that the age at which feral children were discovered consists a fundamental factor for their linguistic development. When found before puberty and with intense tutoring and linguists' support, those children appeared to be more open and sensitive to language and they managed to achieve a medium level in language acquisition. Production of short utterances with fundamental syntactic organization, acknowledgement of a question or even joining in a dialogue-with an extremely simplified form and meaning- were some of the fulfillments that are in favour of the Critical Period Hypothesis.

Striking evidence for the existence of the critical period was provided by Genie, a thirteen year-old girl that was kept in isolation with no exposure to any linguistic input or visual stimulus; she was like a mute while having the ability to talk, deaf while being perfectly able to hear and blind with no problems as far as her eyesight is considered. Genie, despite the many hours of close attention and teaching was never able to grasp language features and the final results were the mastering of a vocabulary of a hundred words as well as the production of utterances that were, till some primary level, syntactically governed.

If the crucial period for the acquisition of language cases to exist, then its light is impossible to be re-attained and feral children seem to be the living proof of this theory; the theories that were available through papers and books were tested and confirmed Critical Period Hypothesis. No matter how many hours were spent, vast number of innovative theories set to action for the joining in of this children in the language mastering, they were incapable of develop a complete linguistic system.


Critical Period Hypothesis appears to be the link, the factor for success in linguistic development and competence. It applies in most cases and explains why children seem to be truly able language learners that master a language system no matter how ignorant they seem to be, with a limited span for word knowledge. Age is with their side!


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