Introduction: Whys and Why Nots of the Critical Period Hypothesis for Second Language Acquisition
David Birdsong University of Texas
The facts of adult second language acquisition (L2A) contrast sharply with those of first language acquisition (L1A). Whereas the attainment of full linguistic competence is the birthright of all normal children, adults vary widely in their ultimate level of attainment, and linguistic competence comparable to that of natives is seldom attested. A reasonable explanation for the facts of UA and L2A is given by the Critical Period Hypothesis (CPH). In its most succinct and theoryneutral formulation, the CPH states that there is a limited developmental period during which it is possible to acquire a language, be it Ll or L2, to normal, nativelike levels. Once this window of opportunity is passed, however, the ability to learn language declines. Consistent with the CPH are the morphological and syntactic deficits of Genie, who was largely deprived of linguistic input and interaction until age 13 ( Curtiss, 1977), as well as the desultory linguistic achievements of most adult L2 learners.
With a focus primarily on L2A, the present volume explores reasons why humans might be subject to a critical period for language learning. It also examines the adequacy of the CPH as an explanatory construct, the "fit" of the hypothesis with the facts.
To both of these dimensions, the contributors offer cutting-edge thought and experimentation. In examining the possible causes of a