Published online by Cambridge University Press: 13 June 2014
Modern methods of investigation in conscious subjects have shown that in normal brain, language is catered for by several essential areas localised in the frontal and temperoparietal cortex and by widely dispersed neurones that serve subsidiary, specialised linguistic functions. These sensory specific, phonological, articulatory and semantic ‘modules’ are activated in parallel. A relatively limited amount of language heard during the sensitive period, when one or other cerebral hemisphere usually becomes dominant for language, is all that is required for any normal child to develop fluency. The specific details of the code, or ‘set’, developed are dependent on the language of the child's environment; they are culturally acquired, but the propensity for language is inborn. During this sensitive period, two languages may be as easily accommodated as one. In stark contrast to the acquisition of natural bilingualism, after about the age of 10 years, any new language is acquired with difficulty for it must be translated into the individual's established language or languages. If a nation is to become bilingual, full advantage of the evanescent sensitive period must be taken by regularly exposing the pre-school child, rather than the older child undergoing formal education, to two languages.