Critical period hypothesis
The Critical Period Hypothesis (CPH) is a theory in psychology and linguistics suggesting that there is a specific window in early life during which individuals can acquire language with native-like fluency. This critical period is generally thought to encompass childhood and adolescence, with many theorists proposing it begins at birth and ends around puberty, although some suggest it may extend to the late teens or early twenties. According to the hypothesis, while individuals can learn languages outside this period, they typically do so with less proficiency and without the ability to achieve a native accent.
The hypothesis gained traction through the work of researchers like Wilder Penfield, Lamar Roberts, and Eric Lenneberg, who posited that the brain's capacity for language acquisition is more flexible in younger ages. They argued that exposure to language in a rich linguistic environment is crucial for full development. The theory has been supported by various studies, including those examining individuals with interrupted language development, but it remains a subject of debate among linguists. Some researchers contend that factors such as universal grammar and the influence of adult speech play significant roles in language learning, suggesting that the mechanics of language acquisition are complex and multifaceted. Overall, the CPH highlights the importance of early exposure to language for achieving fluency.
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Critical period hypothesis
The critical period hypothesis is a concept in psychology and linguistics proposing that people can acquire language with full fluency only during a specific period in life. Although some language learning can occur outside this period, according to the hypothesis, the learner will develop less proficiency, will have a harder time learning, and will not acquire an accent. Within this period, which is during childhood and adolescence, language learning comes more readily, and the person can attain the language of a native speaker. Not all linguists accept this theory, and efforts to prove the theory have been inconclusive.
Background
Researchers believe that nearly all people learn at least one language with the fluency of a native speaker by the age of five. Those who are exposed regularly to more than one language may achieve native fluency in multiple languages by this age. Beyond that, researchers do not always agree on how language is learned.
Some experts believe infants and children are naturally equipped to understand patterns of speech because the patterns are similar even if the languages are not. This is called the theory of universal grammar. Others believe that adults play a large role in how children learn language. This group proposes that the way adults speak to children is key and that this nurturing act is more important than nature in children's language development.
Neither theory accounts for the mechanics of how language learning occurs. It is also unclear what goes wrong when language disorders occur. However, most experts agree that the childhood period is critical to language formation.
The critical period hypothesis originated with the 1959 book Speech and Brain Mechanisms. Coauthors Wilder Penfield and Lamar Roberts were interested specifically in how the brain functions in learning a language. As part of this study, they stated that children up to the age of nine are readily able to learn more than one language. They thought this had to do with the function of the left hemisphere, or half, of the brain. They added that children who hear and speak multiple languages learn to communicate in multiple languages without the need to think in one language and translate to the other, as those who learn a second language later in life do.
Linguist Eric Lenneberg agreed with what Penfield and Roberts included in their book. He expanded their theory further to assert that children who did not acquire a language during this critical period would not be able to learn to speak with any degree of fluency. According to Lenneberg, until thirteen years of age, language acquisition happens in both hemispheres of the brain. After this time, language learning is focused in the left hemisphere, as Penfield and Roberts had stated. According to Lenneberg, this change to specialization of brain functions meant that language learning does not occur as easily, and if a person has not acquired at least one language during this critical period, it is unlikely to happen. As a result of his theories, Lenneberg is considered the father of the critical period hypothesis.
Overview
According to the critical period hypothesis, there is an ideal time in childhood when language acquisition is most likely to occur and result in full fluency. Various age ranges for this critical period have been proposed. Some believe the period begins at birth, while others propose it begins at around age two. Most who support the hypothesis put the end point at puberty, or somewhere between the ages of nine and sixteen. Others suggest that it ends in the late teens or as late as age twenty-two. Some experts have proposed that the critical period starts in infancy and that beginning between the ages of six and nine, the ability to learn a language gradually declines into adulthood. Those who accept the hypothesis generally agree that changes in the brain lead to the loss of ability to learn either a first or an additional language.
The theory has been difficult to prove in a way that satisfies all linguistic experts. Those who attempt to learn a second language as an older adolescent or as an adult have experienced the challenges that come with learning a second language. Research has documented that those who learn either a first or an additional language during the critical period develop greater fluency and a natural sounding accent whereas those who learn the same languages beyond this period are generally less fluent and do not acquire the ability to pronounce sounds that are unique to that language.
Researchers have attempted to prove the theory by studying people who have had their language development interrupted in some way. They have conducted research with people who are deaf who are taught American Sign Language (ASL), people who have had tracheotomy tubes in their throats that prevented normal speech, and people who have lost language through injury or illness. The research has indicated that older people have difficulty acquiring language and that the earlier a person is exposed to language or a second language, the easier it is for them to learn it. However, none of the tests have conclusively documented a critical period.
Some of the most intriguing studies have involved children who were neglected to the extent that they had little or no exposure to language. After these children were rescued from these situations, efforts were made to teach them to speak. Most of these children learned little or no language unless they had had some exposure to it before the age of three.
One of the most famous situations involving one of these feral children was that of "Genie," a thirteen-year-old girl found in Los Angeles in 1970. The child received the name Genie to protect her real identity after it was revealed that she had been starved, neglected, and otherwise abused since early childhood. She had no language skills and lacked even basic social and personal hygiene skills. Because Genie already had reached puberty, researchers believed that if she could be taught to speak, the critical period hypothesis would be disproved.
Genie learned to understand a few more words but never learned to speak in grammatical sentences and never advanced beyond the linguistic abilities of a very young child. Some considered this evidence that the critical period hypothesis was correct. However, others said that Genie had been so neglected and abused that she could have had other developmental issues that interfered with language development, so nothing about her situation confirmed or denied the hypothesis.
Bibliography
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