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Stay Connected to PBS Subscribe to our Previews newsletter for a sneak peek at your favorite programs. Check Out PBS Video Watch local and national programs from anywhere at anytime. Please help improve it or discuss these issues on the talk page. This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. This article needs additional citations for verification. 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 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. In second-language acquisition, the strongest empirical evidence for the critical period hypothesis is in the study of accent, where most older learners do not reach a native-like level. Lenneberg’s critical period hypothesis states that there are maturational constraints on the time a first language can be acquired. 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.