Critical Period Hypothesis

The critical period hypothesis holds that there is a maturationally limited window during which language can be acquired to a native-like level.

Definition

The hypothesis that the ability to acquire language to native proficiency declines or ends after a maturationally defined period in development.

Scope

This topic covers the original formulation of the hypothesis, the evidence from late first-language deprivation, age-of-acquisition effects in second-language learning, and the debate over whether the window is a sharp critical period or a gradual sensitive period and whether it applies equally across linguistic domains. It describes the hypothesis and the evidence bearing on it.

Core questions

• Is there a maturational deadline for native-like language acquisition?
• Does any such period apply equally to phonology, syntax, and the lexicon?
• Is the decline an abrupt critical period or a gradual sensitive period?

Key concepts

• sensitive period
• age of acquisition
• maturation
• language deprivation
• native-like attainment

Key theories

Maturational critical period

Lenneberg's proposal that language acquisition is tied to brain maturation and is most readily accomplished before puberty, after which native attainment becomes difficult.

Age-of-acquisition gradient

Johnson and Newport's finding that grammatical proficiency in second-language learners declines steadily with later age of arrival, evidence often read as a maturational constraint.

History

Lenneberg proposed the hypothesis in 1967 on neurological grounds. Cases of extreme deprivation such as Genie, and Johnson and Newport's 1989 second-language study, became central, although whether the data show a true critical period remains debated.

Debates

Critical period versus continuous decline

Whether the data indicate a sharply bounded critical period after which acquisition fails, or a gradual, continuous decline in learning ability with age.

Key figures

• Eric Lenneberg
• Elissa Newport
• Jacqueline Johnson

Seminal works

• lenneberg1967
• johnsonnewport1989

Frequently asked questions

What does the case of Genie show?

Genie, isolated from language until age 13, later acquired vocabulary but never developed normal grammar, a pattern often cited as consistent with a critical period for first-language syntax, though the case is confounded by abuse and deprivation.