Second Language Acquisition and the Critical Period Hypothesis

st the existence of a critical period. He is particularly well suited to this task, having "changed sides" on the issue in the early 1990s. After the background section, Birdsong goes on to present a careful summary of each of the chapters in the book. While admitting his adherence to the "anti-CPH" camp, he makes no attempt to resolve the evidence presented in the various chapters, and concludes that in total the contributions to the book demonstrate "the richness, depth and breadth of the critical period enquiry" and that they "testify to the unmistakable centrality of the CPH in L2A research" (p. 18). The introduction is clearly written, and since it contains so much summarising material it can stand as a valuable survey of the field in itself. However, some of the chapters in the book do not lend themselves to brief summaries (the chapter by Eubank and Gregg, for example, is far too broad in scope) and thus reading the introduction is no substitute for reading the entire book. [-2-]

There are three chapters providing evidence for the existence of an SLA critical period. First, Weber-Fox and Neville take a frontal approach to the issue with an investigation of neural activity while performing L2 tasks in subjects whose first exposure to L2 was at different ages. Their paper has the rather daunting title of "Functional Neural Subsystems Are Differentially Affected by Delays in Second Language Immersion: ERP and Behavioural Evidence in Bilinguals." The findings do not point to the existence of a single critical period; the patterns of change vary for different language tasks. The authors claim, fairly circumspectly, that "our findings are consistent with the hypothesis that the development of at least some neural subsystems for language processing is constrained by maturational changes, even in early childhood. Additionally, our results are compatible, at least in part, with aspects of Lenneberg's . . . original hypothesis that puberty may mark a significant point in language learning capacity and neural reorganization capabilities" (pp. 35-36). Eubank and Gregg, in a wide-ranging paper entitled "Critical Periods and (Second) Language Acquisition: Divide et Impera," recognise the importance of neurological investigation in their consideration of whether second language learners retain access to Universal Grammar, and find Weber-Fox and Neville's line of research a promising one. Sandwiched between these two chapters comes a paper by Hurford and Kirby which takes a very different approach to the problem. The writers' argument is an evolutionary one; they produce computer models to suggest that a critical period for language acquisition finishing at puberty inevitably evolves in order to produce maximum language learning by the time a reproductive age is reached. However, their argument appears predicated on the assumption that the level of an individual's language knowledge governs the likelihood of his or her being able to reproduce. Alas, it has never been my personal experience that linguistic ability provides a crucial advantage in th

e competition for sexual partners, and I do not find myself convinced in any great measure by this application of the currently fashionable evolutionary approach to exploring the nature of the human mind.

Then come three chapters arguing against the existence of a critical period. James Flege provides research evidence to show that level of achievement in pronunciation is closely related to age of first exposure to the second language. He claims that, even for children, the later in life the first exposure to L2, the greater the degree of foreign accent, with no sudden discontinuity in the figures at a certain age to suggest that a critical [-3-] period has ended, a window of opportunity suddenly closed. Other hypotheses, he claims, can be advanced to explain the linear nature of the relationship between age of first exposure and L2 pronunciation, notably that pronunciation of L2 varies as a function of how well one pronounces L1. Theo Bongaerts takes a very different approach in his paper, which again focusses on pronunciation; his view is that people who begin learning L2 later in life can sometimes achieve native-like pronunciation. If such learners do indeed exist, and Bongaerts presents evidence to suggest that they do, then there can be no biological window of learning opportunity that closes at a fixed age; instead, there must be other explanations for the lack of success of the majority of learners. These two papers, then, while arriving at the same conclusion with regard to the existence of an L2 critical period, do so on the basis of more or less contradictory evidence! Finally, Bialystok and Hakuta, focussing primarily on syntax rather than pronunciation, again point to the lack of any age-related discontinuity in the nature of L2 acquisition. They also suggest that belief in a critical period may be the result of misattribution of causality in examining the evidence; even the neurological differences pointed out by Weber-Fox and Neville could be the result of differences in the learning experience, rather than causes of such differences.

This is all somewhat confusing, and the only conclusion that a reader can come to at the end of the book is that there are no easy answers on the CPH. What is clear is that the old notion that the nature of L2 acquisition changes suddenly and dramatically at around the age of 12-13 because of changes in the brain is much too simplistic (as has been generally recognised for some time). If there is any truth in the CPH, then there may be different critical periods for different language skills, different types of change at different ages. If on the other hand there is no physical change in the brain which can be directly related to language learning, other powerful explanations are needed to account for the dramatic decline in ultimate achievement generally seen in later second language learners compared to young children -- and such explanations are no more than tentative guesses at present. None of this is of much immediate help to the practising language teacher; it may even be in the long run that exact age of first L2 exposure and the CPH will not turn out to be such a central issue after all, at least

《Second Language Acquisition and the Critical Period Hypothesis》