The critical period hypothesis is the subject of a long-standing debate in linguistics and language acquisition over the extent to which the ability to acquire language is biologically linked to age. The hypothesis claims that there is an ideal time window to acquire language in a linguistically rich environment, after which further language acquisition becomes much more difficult and effortful. The critical period hypothesis states that the first few years of life is the crucial time in which an individual can acquire a first language if presented with adequate stimuli. If language input does not occur until after this time, the individual will never achieve a full command of language—especially grammatical systems.
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The critical period hypothesis is the subject of a long-standing debate in linguistics and language acquisition over the extent to which the ability to acquire language is biologically linked to age. The hypothesis claims that there is an ideal time window to acquire language in a linguistically rich environment, after which further language acquisition becomes much more difficult and effortful. The critical period hypothesis states that the first few years of life is the crucial time in which an individual can acquire a first language if presented with adequate stimuli.
If language input does not occur until after this time, the individual will never achieve a full command of language—especially grammatical systems.
The evidence for such a period is limited, and support stems largely from theoretical arguments and analogies to other critical periods in biology such as visual development , but nonetheless is widely accepted.
The nature of such a critical period, however, has been one of the most fiercely debated issues in psycholinguistics and cognitive science in general for decades. Some writers have suggested a "sensitive" or "optimal" period rather than a critical one; others dispute the causes physical maturation, cognitive factors. The duration of the period also varies greatly in different accounts.
The discussion of language critical period suffers from the lack of a commonly accepted definition of language. Some aspects of language, such as phoneme tuning , grammar processing, articulation control , and vocabulary acquisition have weak critical periods and can be significantly improved by training at any age.
The critical period hypothesis was first proposed by Montreal neurologist Wilder Penfield and co-author Lamar Roberts in their book Speech and Brain Mechanisms ,  and was popularized by Eric Lenneberg in with Biological Foundations of Language. Lenneberg's critical period hypothesis states that there are maturational constraints on the time a first language can be acquired.
First-language acquisition relies on neuroplasticity. If language acquisition does not occur by puberty, some aspects of language can be learned but full mastery cannot be achieved.
Support for the critical period theory stems largely from theoretical arguments and analogies to other critical periods in biology such as visual development. Strictly speaking, the experimentally verified critical period relates to a time span during which damage to the development of the visual system can occur, for example if animals are deprived of the necessary binocular input for developing stereopsis.
It has however been considered "likely",  and has in many cases been flatly presented as fact, that experimental evidence would point to a comparable critical period also for recovery of such development and treatment ; however this is a hypothesis. Recently, doubts have arisen concerning the validity of this critical period hypothesis with regard to visual development, in particular since the time it became known that neuroscientist Susan R. Barry and others have achieved stereopsis as adults, long after the supposed critical period for acquiring this skill.
Recently, it has been suggested that if a critical period does exist, it may be due at least partially to the delayed development of the prefrontal cortex in human children. This pattern of prefrontal development is unique to humans among similar mammalian and primate species, and may explain why humans—and not chimpanzees—are so adept at learning language. The theory has often been extended to a critical period for second-language acquisition SLA , although this is much less widely accepted.
Certainly, older learners of a second language rarely achieve the native-like fluency that younger learners display, despite often progressing faster than children in the initial stages. While the window for learning a second language never completely closes, certain linguistic aspects appear to be more affected by the age of the learner than others.
For example, adult second-language learners nearly always retain an immediately identifiable foreign accent, including some who display perfect grammar.
Adults learning a new language are unlikely to attain a convincing native accent since they are past the prime age of learning new neuromuscular functions, and therefore pronunciations.
Writers have suggested a younger critical age for learning phonology than for morphemes and syntax. The plasticity of procedural memory is argued to decline after the age of 5. The attrition of procedural memory plasticity inhibits the ability of an L2 user to speak their second language automatically. It can still take conscious effort even if they are exposed to the second language as early as age 3.
This effort is observed by measuring brain activity. L2-users that are exposed to their second language at an early age and are everyday users show lower levels of brain activity when using their L1 than when using their L2. This suggests that additional resources are recruited when speaking their L2 and it is therefore a more strenuous process. The critical period hypothesis in SLA follows a "use it then lose it" approach, which dictates that as a person ages, excess neural circuitry used during L1 learning is essentially broken down.
The structures necessary for L1 use are kept. On the other hand, a second "use it or lose it" approach dictates that if an L2 user begins to learn at an early age and continues on through his life, then his language-learning circuitry should remain active. This approach is also called the "exercise hypothesis". There is much debate over the timing of the critical period with respect to SLA, with estimates ranging between 2 and 13 years of age.
For instance, if an SLA researcher is studying L2 phonological development, they will likely conclude that the critical period ends at around age 3. If another SLA researcher is studying L2 syntactical development, they may conclude that the critical period ends at a much later age. These differences in research focus are what create the critical period timing debate. Some writers have argued that the critical period hypothesis does not apply to SLA, and that second-language proficiency is determined by the time and effort put into the learning process, and not the learner's age.
A combination of these factors often leads to individual variation in second-language acquisition experiences. On reviewing the published material, Bialystok and Hakuta conclude that second-language learning is not necessarily subject to biological critical periods, but "on average, there is a continuous decline in ability [to learn] with age.
How children acquire native language L1 and the relevance of this to foreign language L2 learning has long been debated.
Although evidence for L2 learning ability declining with age is controversial, a common notion is that children learn L2s easily, whilst older learners rarely achieve fluency. A CP was popularised by Eric Lenneberg in for L1 acquisition, but considerable interest now surrounds age effects on second-language acquisition SLA.
SLA theories explain learning processes and suggest causal factors for a possible CP for second language acquisition. These SLA-CP theories mainly attempt to explain apparent differences in language aptitudes of children and adults by distinct learning routes, and clarify these differences by discussing psychological mechanisms. Research explores these ideas and hypotheses, but results are varied: some demonstrate pre-pubescent children acquire language easily, and some that older learners have the advantage, whilst others focus on existence of a CP for SLA.
Recent studies e. Mayberry and Lock, have recognised certain aspects of SLA may be affected by age, whilst others remain intact. The objective of this study is to investigate whether capacity for vocabulary acquisition decreases with age. Other work has challenged the biological approach; Krashen re-analysed clinical data used as evidence and concluded cerebral specialisation occurs much earlier than Lenneberg calculated.
Therefore, if a CP exists, it does not coincide with lateralisation. Despite concerns with Lenneberg's original evidence and the dissociation of lateralisation from the language CP idea, however, the concept of a CP remains a viable hypothesis, which later work has better explained and substantiated. A review of SLA theories and their explanations for age-related differences is necessary before considering empirical studies.
The most reductionist theories are those of Penfield and Roberts and Lenneberg , which stem from L1 and brain damage studies. Children who suffer impairment before puberty typically recover and re- develop normal language, whereas adults rarely recover fully, and often do not regain verbal abilities beyond the point reached five months after impairment. Both theories agree that children have a neurological advantage in learning languages, and that puberty correlates with a turning point in ability.
They assert that language acquisition occurs primarily, possibly exclusively, during childhood as the brain loses plasticity after a certain age. It then becomes rigid and fixed, and loses the ability for adaptation and reorganisation, rendering language re- learning difficult. Penfield and Roberts claim children under nine can learn up to three languages: early exposure to different languages activates a reflex in the brain allowing them to switch between languages without confusion or translation into L1 Penfield, Lenneberg asserts that if no language is learned by puberty, it cannot be learned in a normal, functional sense.
Cases of deaf and feral children provide evidence for a biologically determined CP for L1. A classic example is 'Genie' , a victim of child abuse who was deprived of social interaction from birth until discovered aged thirteen. Her father had judged her retarded at birth and had chosen to isolate her. She was kept strapped to a potty chair and forced to wear diapers. She was completely without language.
Her case presented an ideal opportunity to test the theory that a nurturing environment could somehow make up for the total lack of language past the age of After seven years of rehabilitation Genie still lacked linguistic competence, although the degree to which she acquired language is disputed. She also had no language skills, but, unlike Genie, quickly acquired normal language abilities through systematic specialist training. Such studies are problematic; isolation can result in general retardation and emotional disturbances, which may confound conclusions drawn about language abilities.
Newport and Supalla  studied ASL acquisition in deaf children differing in age of exposure; few were exposed to ASL from birth, most of them first learned it at school. Results showed a linear decline in performance with increasing age of exposure; those exposed to ASL from birth performed best, and 'late learners' worst, on all production and comprehension tests. Their study thus provides direct evidence for language learning ability decreasing with age, but it does not add to Lenneberg's CP hypothesis as even the oldest children, the 'late learners', were exposed to ASL by age four, and had therefore not reached puberty, the proposed end of the CP.
In addition, the declines were shown to be linear, with no sudden 'drop off' of ability at a certain age, as would be predicted by a strong CP hypothesis. That the children performed significantly worse may suggest that the CP ends earlier than originally postulated. However, this decline in performance may also be attributed in part to limitations of second language acquisition for hearing parents learning ASL.
Contrary to biological views, behavioural approaches assert that languages are learned as any other behaviour, through conditioning. Skinner details how operant conditioning forms connections with the environment through interaction and, alongside O.
Hobart Mowrer , applies the ideas to language acquisition. Because new connections between behaviour and the environment are formed and reformed throughout life, it is possible to gain new skills, including language s , at any age.
To explain observed language learning differences between children and adults, children are postulated to create countless new connections daily, and may handle the language learning process more effectively than do adults. This assumption, however, remains untested and is not a reliable explanation for children's aptitude for L2 learning.
Problematic of the behaviourist approach is its assumption that all learning, verbal and non-verbal, occurs through the same processes. A more general problem is that, as Pinker notes, almost every sentence anybody voices is an original combination of words, never previously uttered, therefore a language cannot consist only of word combinations learned through repetition and conditioning; the brain must contain innate means of creating endless amounts of grammatical sentences from a limited vocabulary.
This is precisely what Chomsky reprinted as Chomsky argues with his proposition of a universal grammar UG. Chomsky asserts that environmental factors must be relatively unimportant for language emergence, as so many different factors surround children acquiring L1. Instead, Chomsky claims language learners possess innate principles building a ' language acquisition device ' LAD in the brain. These principles denote restricted possibilities for variation within the language, and enable learners to construct a grammar out of 'raw input' collected from the environment.
Input alone cannot explain language acquisition because it is degenerated by characteristic features such as stutters, and lacks corrections from which learners discover incorrect variations. Singleton and Newport demonstrate the function of UG in their study of 'Simon'. Simon learned ASL as his L1 from parents who had learned it as an L2 after puberty and provided him with imperfect models.
Results showed Simon learned normal and logical rules and was able to construct an organised linguistic system, despite being exposed to inconsistent input. Chomsky developed UG to explain L1 acquisition data, but maintains it also applies to L2 learners who achieve near-native fluency not attributable solely to input and interaction Chomsky Although it does not describe an optimal age for SLA, the theory implies that younger children can learn languages more easily than older learners, as adults must reactivate principles developed during L1 learning and forge an SLA path: children can learn several languages simultaneously as long as the principles are still active and they are exposed to sufficient language samples Pinker, The parents of Singleton and Newport's patient also had linguistic abilities in line with these age-related predictions; they learned ASL after puberty and never reached complete fluency.
There are, however, problems with the extrapolation of the UG theory to SLA: L2 learners go through several phases of types of utterance that are not similar to their L1 or the L2 they hear.
Critical period hypothesis
In second language acquisition research, the critical period hypothesis cph holds that the function between learners' age and their susceptibility to second language input is non-linear. This paper revisits the indistinctness found in the literature with regard to this hypothesis's scope and predictions. Even when its scope is clearly delineated and its predictions are spelt out, however, empirical studies—with few exceptions—use analytical statistical tools that are irrelevant with respect to the predictions made. This paper discusses statistical fallacies common in cph research and illustrates an alternative analytical method piecewise regression by means of a reanalysis of two datasets from a paper purporting to have found cross-linguistic evidence in favour of the cph.
Lenneberg's Critical Period Hypothesis
One of the crucial underlying concepts that account for the differences in second language acquisition SLA between children and adults is the critical period hypothesis. Eric Lenneberg hypothesised that language acquisition in human beings was affected by biological growth i. In his claims, the age of adolescence after puberty, about 13 years old is a transitional point at which the brain reaches a biologically mature state. Because of this, there is a firm localisation of language processing in the left hemisphere of the brain i. This then, causes difficulties in language acquisition after puberty. Although the critical period hypothesis was originally applied to L1 acquisition, studies have shown that the effects are also extended to L2 acquisition. For example, a research conducted by Jacqueline S.
Critical Period Hypothesis
Skip to content. The critical period hypothesis says that there is a period of growth in which full native competence is possible when acquiring a language. This period is from early childhood to adolescence. The critical period hypothesis has implications for teachers and learning programmes, but it is not universally accepted. Acquisition theories say that adults do not acquire languages as well as children because of external and internal factors, not because of a lack of ability. Example Older learners rarely achieve a near-native accent.
It consists, roughly, in the idea that a certain age is appropriate for learning a language, so that it is impossible to achieve full competence before or after it. In this essay, I will focus on the second borderline, which is usually drawn by later interpreters at the beginning of puberty — the reasonability of this will be discussed in the next chapter of this essay. Lenneberg subdivides the ongoing process of lateralization into five levels: an infant up to 20 months has identical hemispheres without functional differences; a toddler up to 36 months develops a preference for either the right or the left hand, but the responsibility for language still can easily switch an other hemisphere; a child up to 10 years is still able to reactivate language functions in the right hemisphere; in the early puberty — up to 14 years — the equipotentiality rapidly declines, and after that it is lost completely. He thereby implies that at the beginning this function is present in both hemispheres and later partly disappears from the right one; it does not develop in the left half of the brain only right from the start with the option to migrate to the other hemisphere in emergency cases during the childhood.