Learning a Language, Best Age

A controversial topic among linguists and researchers is the critical period hypothesis (CPH) and research studies that pertain to the best age in which to learn a language. CPH was first proposed by neurologist Wilder Penfield and coauthor Lamar Roberts in 1959. CPH claims that the presentation of adequate stimuli during the first few years of life are critical for individuals to acquire a first language, According to the theory, if language input does not occur during this period, the individual will never achieve a full command of the language—especially the grammatical systems. CPH was popularized in 1967 by Eric H. Lenneberg, with the introduction of his book Biological Foundations of Language.

Lenneberg's theory has extended to include a critical period for second-language acquisition (SLA) and has influenced research in the field, which is evidenced by studies including those supportive and unsupportive of CPH. Generally, researchers in the field of SLA have explored the following questions:

• 1.
  Does age affect how fast we can learn or acquire a second language over a reasonable period?
• 2.
  Does the type of exposure to the second language relate to age?
• 3.
  Does the age at which we begin learning a second language affect how fluent we can become in that language after a long time?
• 4.
  Do all these effects hold for all levels or types of linguistic knowledge?

This entry considers studies that have tried to look at both early-stage performance and ultimate attainment of those language learners studied. Results of studies in second-language acquisition indicate researchers are divided in their positions regarding CPH. Some researchers support CPH and insist that a critical period for learning a language does exist. For example, Mark Patkowski conducted a study about the likelihood of a critical period for learning a second language that found that learners younger than age 15 achieved a higher syntactic proficiency than did those who were older than age 15 at the onset of exposure. Among all factors Patkowski examined, age was the factor that had the most significant impact for success in learning a second language.

Results of some studies are mixed. For example, Stephen D. Krashen found in a 1973 study that adult learners proceeded through the early stages of syntactic and morphological development faster than children did, and that older children acquired this growth faster than younger children who were in the early stages of language development. Similarly, Anna K. Fathman and Lois Precup, in their 1983 study of immigrants acquiring English as a second language in the United States, reported that those who had immigrated at a younger age achieved higher levels of phonetic/ phonological proficiency than later arrivals. However, an opposing pattern was found in respect to morpho-syntactic proficiency. A similar example is the 1999 study by Ellen Bialystok and Brenda A. Miller; they replicated the 1989 study of Jacqueline Johnson and Elissa Newport, and found differences in the performance on a grammar judgment test between native speakers of Chinese and Spanish acquiring English, before the age of 15. Although the younger Spanish-English bilinguals showed an advantage in performance over the older participants, the same pattern did not apply to Chinese-English bilinguals. They conclude that their results do not provide enough evidence to support the critical period hypothesis when acquiring a second language.

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