are just as likely to be altered by cognitive processes as cognitive processes are to be determined by neurological structures. It is not surprising that the experience and knowledge we accumulate as we grow changes the way in which new information, including new languages, will be represented and that these differences can be detected as different patterns of neural organization in the brain. Indeed, brain patterns vary in the population: In some people, language is lateralized to the right hemisphere instead of the left, but they can still write, draw, and throw a baseball. The only issue is whether or not learning is impaired by these differences and whether the critical variable in determining the difference is age of first exposure. Here, only behavioral evidence is relevant, and the behavioral evidence does not make a sufficiently compelling case.
A more unusual argument for a critical period in language acquisition (but not specifically second language acquisition) was offered by Hurford ( 1991; see also Hurford & Kirby, chap. 3, this volume). Using computer modelling to simulate population growth and evolution, he demonstrated how a critical period for language acquisition is an adaptive feature in population terms. His explanation was that there is no selective pressure to keep the capacity for language learning available after puberty, so it turns off. The argument is interesting, but the amount of conjecture in the discussion is staggering.
Our discussion described some linguistic and cognitive factors involved in the language learning process that both contradict specific claims from the critical period hypothesis and offer an alternative means of explaining the advantage younger learners normally enjoy in second language acquisition. In addition, social factors conspire to ease the effort for young children by providing a nurturing environment, simplified input, educational opportunities, cooperative peers, and other supporting aspects of a social context that facilitate the acquisition of any language. Armed with these problems in the experimental studies designed to support a critical period, unconvinced that performance differences for younger and older learners reflect more than simple correlation, and given alternative explanations for the patterns of data that do occur, we see no reason to reject the null hypothesis that there is no critical period for second language acquisition.
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Bialystok, E., & Hakuta, K. ( 1994). In other words: The science and psychology of second-language acquisition. New York: Basic Books.
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