Critical / Sensitive Period for Second Language Acquisition

 The ability to acquire a second language (L2) is thought to diminish after reaching puberty, a concept referred to as the "critical period" for language acquisition. This hypothesis, first proposed by E. Lenneberg in 1967, suggests that the brain's capacity for language learning decreases significantly as a person ages. The primary reason for this decline is a reduction in neural plasticity—the brain's ability to reorganize and adapt its structure and function in response to new experiences. As individuals reach puberty, specific brain areas responsible for language learning, such as the cerebral cortex, experience structural and chemical changes. These modifications, which include shifts in neurodensity, alterations in the white matter, and changes in the frequency of brain waves, contribute to a decrease in language learning potential.

Research on this hypothesis has profound implications for language teaching. It suggests that there are optimal times to begin learning a second language (L2) and that age may influence the most effective teaching approaches. Understanding when language learning abilities are at their peak could help educators determine the best age for introducing a second language, as well as the most appropriate teaching methods for learners of different ages.

To explore the validity of the critical period hypothesis, the study conducted by Jacqueline Johnson and Elissa Newport (1989) provides valuable insights. Their research examined whether the theoretical framework of the critical period could also be applied to second language acquisition. According to their theory, younger children should have an advantage over adults in acquiring a second language, leading to higher levels of proficiency in the language.

The study involved 46 participants, all native speakers of Chinese or Korean, who had learned English as a second language. The participants were selected based on the age at which they first encountered English. They were divided into two groups: early arrivals, who arrived in the U.S. before the age of 15, and late arrivals, who arrived after the age of 17. The researchers chose this age cut-off to investigate the influence of puberty on language acquisition. The participants were tested on their understanding of English syntax and morphology by judging the grammaticality of spoken English sentences. These sentences varied in complexity, testing rules related to English morphology (e.g., past tense, plural forms) and syntax (e.g., word order, question formation).

The results of the study revealed a strong correlation between the age of arrival in the U.S. and performance in the English proficiency tests. Participants who arrived at an earlier age performed better on the tests than those who arrived later. This finding supports the idea that language learning abilities decline after puberty. In fact, the study showed a clear decline in performance for those exposed to English after puberty, suggesting that language learning abilities are indeed more robust during childhood.

The study also provided evidence that this decline in language learning ability begins before puberty and continues gradually throughout adolescence. The results align with the critical period hypothesis, suggesting that the brain's capacity to learn a language diminishes over time, plateauing at a lower level after puberty. This plateau, however, varies from person to person, with some individuals maintaining higher proficiency levels than others even after the critical period has passed.

In terms of methodological rigor, the research conducted by Johnson and Newport offers strong evidence in support of the critical period hypothesis. The study's design—selecting participants with varied ages of exposure to English, using a standardized language proficiency test, and considering cognitive and social factors—ensures the reliability and validity of the findings. Additionally, the researchers accounted for important variables such as motivation, integration into English-speaking communities, and the time available for practicing the language.

In conclusion, the findings from Johnson and Newport’s study contribute significantly to our understanding of the critical period for second language acquisition. These results suggest that language learning abilities are influenced by biological and cognitive factors, but also by socio-cultural elements such as motivation and exposure to the language. The study affirms that critical periods in human development play a key role in language acquisition, and it highlights the importance of considering both age and contextual factors when designing language learning programs.

References

Johnson, J. S., & Newport, E. L. (1989). Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cognitive Psychology, 21(1), 60-99. https://doi.org/10.1016/0010-0285(89)90003-0