CRITICAL PERIOD

A period early in life during which a human being is uniquely endowed with the capacity to acquire a first language. Also applied to second language acquisition. Some commentators prefer the term sensitive period, arguing that language can be acquired outside the period, even if less completely.

Lenneberg (1967) concluded from studies of brain lateralisation that there was a period up to puberty during which the configuration of the brain was flexible. If there were damage to the left hemisphere during this period, the language faculty could relocate itself on the right. A parallel was traced between the timing of lateralisation and evidence from language deprivation. Children deprived of language go on to develop full linguistic competence if they are brought into society before the age of about eight or nine; those who are rescued at a later stage may develop an extensive vocabulary but often manifest an incomplete system of syntax. Hence a conclusion that lateralisation was closely associated with the acquisition of a first language and that, if acquisition were to be fully successful, it had to occur during the period of flexibility.

 In fact, the evidence is not as clear as was once suggested. Not all children who suffer left-hemisphere damage develop a right-hemi sphere dominance for language; while adults with left-hemisphere damage may sometimes do so. There is evidence shortly after birth that a degree of lateralisation has taken place, and the process may be complete by five years old. Importantly, brain imaging technology has shown us that language is much more widely distributed in the brain than was once thought.

The deprivation evidence is also open to challenge. There is considerable variation in the way deprived children develop, and no evidence of a sharply defined point when language is no longer achievable. Account must also be taken of the background of the cases studied and the extent to which early trauma may have affected the ability to acquire language and to relate to others.

If there is indeed a sensitive period, there are other possible explanations besides the purely neurological one:

An innate Universal Grammar may be available to the infant for only a limited period; or it may be suppressed by the development of adult cognitive capacities more suitable for ‘problem-solving’ but less apt for the acquisition of language.

 Maturation may provide for a stage when a successfully internalised set of grammar rules becomes separated from the evidence which gave rise to it.

 Modified input (child directed speech) is less likely to be addressed to older children than to infants.

The ‘less is more’ hypothesis suggests that, precisely because an infant is not fully developed cognitively, its limited attention span enables it to focus on discrete aspects of the input.

The notion of a critical period has been extended to second language acquisition and is sometimes cited in support of an early start for foreign language learning. The evidence is complex and mixed. A distinction has to be made between the rate at which a second language is acquired and the final level of competence that is achieved. Contributory factors to be taken into account include: age at which acquisition begins (age of arrival in the case of immigrant learners), length of exposure, type of input (naturalistic, immersion, classroom) and type of motivation.

The acquisition of a second language can be regarded as the acquisition of a range of skills and information types (phonology, lexis, syntax). Different domains may be differently affected by the age at which acquisition begins. Generalising considerably, it would appear that there may be a critical period (up to the age of eight or nine) for the acquisition of a native or near-native accent. Some evidence suggests that adults initially acquire syntax faster than younger learners; but that adolescents score best, both short term and long term, on a wide range of tasks. Early starting age naturally results in longer exposure. To the extent that these factors can be separated, an early start seems to lead to greater accuracy and long exposure to greater communicative competence.

The question remains of why many adults find it difficult to acquire a second language. Explanations include the loss of the universal grammar which triggers first language acquisition; cognitive develop ment which results in a more analytic approach to the language learning task; intervention of the first language in the process; the loss of perceptual sensitivity with the development of categorical perception; the fact that the adult has a fully developed personality expressible through the medium of L1; and again, the hypothesis that the cognitive limitations of the child make it more sensitive to individual features of linguistic input.

See also: Brain lateralisation, Deprivation, ‘Less is more’, Universal Grammar

Further reading: Aitchison (1998); Birdsong (1999); Singleton (1989); Skuse (1993)

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