A blog for the comprehensive understanding of Literature, Applied Linguistics and ELT

November 15, 2009

Critical Period Hypothesis (CPH)


In his fundamental work, Biological Foundations of Language, 1967, the biolinguist Eric Heinz Lenneberg presents, among other concepts, his “Critical period” hypothesis. Lenneberg's idea of a critical period is an important aspect of the innateness proposal. Lenneberg theorized that the capacity to learn a language is indeed innate, and, like many such inborn mechanisms, it is confined in time. He proposed that there is one critical phase between the age of two and about 13 years (before puberty) in which an individual is able to acquire first language (L1). Beyond this time language becomes increasingly difficult to acquire.

It was Lenneberg's proposition that the end of this "critical period" is determined by a loss of brain plasticity – in particular by the completion of the lateralization of the language function in the left hemisphere. Researchers have debated the age at which lateralization actually occurs. Kinsbourne (1975) proposes completion by birth; Krashen (1973) suggests it may be complete by age 5; Lenneberg (1967) proposes lateralization by puberty. Long (1988) suggests that the brain's loss of plasticity is also due to other aspects of cerebral maturation unrelated to lateralization.

Evidence: Viktor, Genie, deaf signers

Limitations: Despite its strong sides the hypothesis has some limitations. Evidence of various types seems to weaken Lenneberg's hypothesis:

Firstly, neuropsychological evidence shows that brain lateralization "occurs long before the onset of puberty, perhaps during the first year of life" (Flynn and Manuel, 1991: 130).

Secondly, the similar developmental patterns observed in child and adult language acquisition are in contrast with the idea that different processes take place in the two types of learning.
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