Is There a Critical Period for Language Acquisition?

Language is a specific system of the humans to communicate with each other by use of voice, symbols and words. Language development has been an important research subject that questions, among many others, how individuals acquire language and protect and improve it afterwards. Language and thought are in mutual interaction and form a mutual structure as well. In a similar manner, language development and cognitive development are known to take place in parallel to each other. In consideration of the importance of language development, there are lots of researches done until today, which suggest, in conclusion, that there is a specific time frame dedicated for language acquisition, called the “critical period”. This essay discusses weather there is really a critical period for language acquisition or not, through several researches, case studies and suggestions of the important researchers of the field.

Critical period is a time slot during which stimulation must be present for a certain level of development to be achieved. Exposure to the same stimulation after this period either reduces the developmental effects, or does not affect it at all. The critical period hypothesis says that, in the growth stage, there is a period for the individual to establish full command on the language, which is between early childhood and adolescence. In addition, the hypothesis claims that, while older individuals are also able to learn how to speak a language, in this case they lack the native fluidity of younger learners and that language acquisition becomes more difficult and requires much more effort after puberty. According to the critical period hypothesis, there is a limited time period for an individual to acquire the first language (L1) as a native, after which the individual cannot establish full command on the language and on the grammar system in particular (Lenneberg, 1967).

In 1959, Montreal based neurologist Wilder Penfiled (2014) and co-author Lamar Roberts (2014) brought forward the critical period hypothesis for the first time and in 1967, the subject became popular with the book called Biological Foundation of Language by Eric Lenneberg (1967). According to Lenneberg (1967), during puberty, it is the brain lateralisation mechanism, which closes down
the brain’s ability to acquire language. On the other hand, Noam Chomsky (1965), as another well-known researcher in this field, believes that children are born with the inherited ability to learn human language. As indicated by Chomsky (1965), every youngster has a “language acquisition device” or LAD, which encodes the grammatical structures and major principles of a language into
the child’s brain.

According to Lenneberg’s (1967) arguments, there is a critical period for acquisition of language and a limited period for the language to be acquired properly. If language acquisition does not occur in puberty, it can be still acquired, but the full command of language cannot be established afterwards. Lenneberg’s (1967) suggestions can be reviewed in two parts. First, development of the first language starts in childhood, for which a research on brain damage recovery is shown as evidence. Children who suffered from brain damage before puberty period are typically able to fully recover re-develop normal language skills later, while adults who suffered from brain damage are rarely able to reach full language acquisition, and these adults often cannot regain their previous verbal abilities (Hurford, 1991, p. 159). Second, according to Lenneberg (1967), in the human brain, there is a neurological mechanism responsible for the formation of language learning abilities. After the puberty period, individuals loose the plasticity of their brain, which is the organizational capacity needed for language acquisition. This occurs simultaneously with lateralisation of the brain, during which the left hemisphere becomes specialized on language. Development of linguistic and motor skills occurs between ages two and thirteen, during which the functions of the cerebral hemispheres get separated and become fixed, making the attainment of language difficult, if not impossible (Lenneberg, 1967, pp. 389-90).

However, the neurological explanations have challenged by later studies. The studies conducted on congenitally deaf children, the processes of second language learning and feral children are presented as evidences. For instance, Witelson & Pallie (1973) argued that when a child became five years old, lateralisation came to an end. After analysing the critical data that had been provided
as a proof (e.g. from Genesee, 1978), Krashen (1975) deduced that the completion of lateralisation was much earlier than what Lenneberg (1967) figured. As a result, the relevancy between lateralisation and the end of the critical period is inconclusive, considering children can learn language with ease till the age of twelve: If a critical period does exist, it does not occur at
the same time with lateralisation. Despite the concerns with Lenneberg’s (1967) original evidence and the separation of lateralisation from the idea of a critical period for language acquisition, the concept of the biologically based critical period remains feasible in itself, for which more direct and reliable evidences have been adduced later.

Feral children are the ones who have lived away from human connection since a very young age and have not experienced the exigence of language acquisition. ‘Victor’ is one of the examples for this kind of cases (Itard, 1801). Victor was twelve years old when he was discovered by a physician that endeavoured for him for five years to get the ability to speak and read. Victor was able to understand the meanings of many words; however he never became able to speaking. The most known case of this kind is that of ‘Genie’ (Curtiss, 2014). Since Genie was mentally deficient according to her father, she was destitute of human contact from birth to
thirteen years old. It was reported that, when she was found, she was not capable of anything regarding language. Moreover, she was still deficient in lingual skills after seven years of rehabilitation. Isabelle is another instance of similar cases. In despite of being locked up in a pitch-dark room until six and half years old along with her mother who was unable to hear and speak, she had gained an understanding of gestures. On the other hand, she did not have any linguistic competence when she was discovered. Isabelle gained language skills fast with the help of psychologists and methodical practice, while Genie was not able to do it (Davis, 1949). The cases mentioned above seem to support critical period hypothesis of Lenneberg (1967). Since Genie and Victor were found after their adolescence period, they could not obtain the skills of a normal language. However, Isabelle had normal language ability because she was discovered before her adolescence. All of these prove that, if human and language contact is provided before the end of the adolescence period, the child can gain language skills (Lenneberg, 1967).

Congenitally deaf children are also take part in the studies, results of which support the critical period hypothesis. There are studies conducted with children who were grown up by deaf parents and exposed the sign language for language acquisition (Newport et al., 1989). According to sources, 90% of deaf children who have hearing parents learn the sign language for the first time at school.
Newport & Supalla tells about “linear decline in performance with increasing age of exposure, on virtually every morpheme tested” (1989, p.78). It shows that, children who are exposed to the sign language from the birth perform better on the tests of production and comprehension, when compared to children who try to learn the sign language later. These results provide an evidence for the reduction in the capacity to acquire language with age.

Researchers have chosen the field of second language acquisition to explain the critical period hypothesis, because it is difficult to directly test the critical period in the acquisition of the first language. According to Seliger (1978), if the biological nature of adulthood really created an insurmountable obstacle for the acquisition of a comprehensive language, then it would have been
almost impossible for adults to learn a second language. Through their study on Cuman immigrants, Asher & Garcia (1969) demonstrated this conception. The study showed that children who arrived in the U.S. between ages one and six had better results in English reading tests than children who arrived in the U.S. between ages seven and nineteen.

From the point of the biological approach to the critical period, Chomsky (1965) proposed a theory for children to learn language more easily, based on “transformational grammar”. Firstly, there is a black box in the brain of the “learner”, which is built by the rules and principles by birth, and the baby is already possessed at that time. According to Hook’s (1969) theory, children learn
language more easily than adults and also children can learn more than one language while their black box is active. To learn a language again (e.g. after having a brain), or to learn a new language, adults have to utilize from the same rules that have thrived in the early ages. Therefore it is more difficult for adults to acquire language.

If any conclusion may be drawn, language is really important for the human to communicate and interact with each other. Language development is linked to cognitive development, which in turn suggests that language is really important for the human to continue life as normal. According to all the studies conducted with feral children and deaf children and the studies on second language learning, younger learners perform better than the older in language acquisition. The outcomes of these studies can draw evidence that there is a critical period for language acquisition.

Clinical Psychologist B. Perim Secmen


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