The critical period hypothesis states that there is a specific and limited time for language acquisition. More specifically, this hypothesis states that the first few years of a child’s life is the critical time in which an individual can acquire language if presented with adequate stimuli. Proponents of the hypothesis argue that if a child does not receive the appropriate stimuli during this “critical period,” then the individual will never achieve full command of language. In other words, once a child passes a certain age without language acquisition, it is not possible to learn language at a later age.
The scientific focus on a critical time for language acquisition began in the late 1950s when neurologist Wilder Penfield discussed language acquisition from a physiological perspective. Penfield pointed to the superiority for learning language demonstrated by young children. He argued that children learn language easily before the age of 9; however, after the age of 9, learning language becomes difficult. Penfield claimed that the reason for this change in the ability to learn language was due to the plasticity of the human brain. The brain of the child is plastic, whereas the adult brain is rigid.
In 1967, linguist Eric Lenneberg further advanced the idea of a critical period for learning language in his classic work, Biological Foundations of Language. Like Penfield, Lenneberg asserted that the acquisition of language, like other biological functions, was successful only when it was stimulated at the right time and in a linguistically stimulating environment. Drawing on evidence from studies of brain growth and from clinical studies of deafness, mental retardation, and brain damage, Lenneberg claimed that there are age constraints on language acquisition caused by brain maturation. He maintained that the critical period for language learning occurs between the ages of 2 and puberty, with the crucial period occurring between 4 and 5 years of age. Lenneberg argued that before the age of 2 the brain has not developed the capacities it needs for learning language. He maintained that after puberty the brain’s lateralization shuts down the brain’s ability to acquire language. Therefore, if an individual did not learn language within the critical period, the individual would never be able to acquire language in any normal sense.
More recently, in 1994, psychologist and cognitive scientist Steven Pinker similarly claimed a critical time period for language acquisition by stating that language is instinctual. Language, Pinker asserted, is a biological adaptation rather than a cultural creation. He asserted that the brain contains innate means of creating an endless number of grammatical sentences from a limited vocabulary. Pinker held that the acquisition of normal language would occur for children up to 6 years of age when properly stimulated. He asserted that, after 6 years of age, the possibility of normal language acquisition declines and is rarely successful after puberty.
What evidence exists to support the critical period hypothesis? A basic limitation of the critical period hypothesis is that testing this theory, using traditional scientific methodology, is unethical. Scientists cannot intentionally isolate a child from the rest of the world for several years and then assess the effects of such isolation on language acquisition. Therefore, scientists have documented evidence of the critical period hypothesis mainly from abused and feral children who grow up deprived of exposure to language in childhood and who, consequently, do not acquire language normally. The most famous example used to demonstrate evidence of this hypothesis is the case of Genie, a pseudonym for a girl discovered in 1974, at the age of 13, strapped to a potty chair and wearing diapers. Genie had little linguistic ability and, over several years of rehabilitation, was unable to acquire language completely, although researchers involved in Genie’s rehabilitation disagreed on the degree to which she acquired the normal use of language.
Critics of the critical period hypothesis point to the use of examples of abused children and feral children as the central limitation of empirical evidence for this hypothesis. They argue that the lack of language in later life may be due to deprived and extreme social and physical environments that cause neurological changes in the brain, rather than specifically to the lack of exposure to language. In addition, behavioral approaches challenge the biological view of language acquisition and maintain that individuals learn language like any other behavior, through positive reinforcement. Therefore, they argue, it is possible to gain new skills, including learning language, at any age.
Researchers have extended the study of the critical period hypothesis to deaf children learning American Sign Language (ASL) and older learners of a second language. For deaf children learning ASL, there is evidence that language learning ability declines with age, but there is no sudden drop off at puberty. Children exposed to ASL at birth become the best at learning the language. Research examining older learners of a second language consistently indicates that most individuals are able to learn a second language when they are well into adulthood. However, there is a continuous decline in the ease of learning a second language with age. Researchers have found that learning a second language from mere exposure to the language declines after puberty. Therefore, in the adult years, the individual wanting to learn a second language has to spend much time and focused effort studying the language. Moreover, research indicates that adult second language learners nearly always retain an identifiable foreign accent that children as second-language learners do not display.
See also Consciousness; Creativity; Language; Memory; Psychology and Time
Bialystok, E., & Hakuta, K. (1994). In other words: The science and psychology of second language acquisition. New York: HarperCollins.
Lenneberg, E. (1967). Biological foundations of language. New York: Wiley.
Penfield, W., & Roberts, L. (1959). Speech and brain mechanisms. Princeton, NJ: Princeton University Press.
Pinker, S. (1994). The language instinct. New York: Morrow.