二语习得里的关键期假说
The critical period hypothesis states that the first few years of life is the crucial time in which an individual can acquire a first language if presented with adequate stimuli. If language input doesn't occur until after this time, the individual will never achieve a full command of language—especially grammatical systems.
The evidence for such a period is limited, and support stems largely from theoretical arguments and analogies to other critical periods in biology such as visual development, but nonetheless is widely accepted. The nature of this phenomenon, however, has been one of the most fiercely debated issues in psycholinguistics and cognitive science in general for decades. others dispute the causes (physical maturation, cognitive factors). The duration of the period also varies greatly in different accounts. In second-language acquisition, the strongest evidence for the critical period hypothesis is in the study of accent, where most older learners do not reach a native-like level. However, under certain conditions, native-like accent has been observed, suggesting that accent is affected by multiple factors, such as identity and motivation, rather than a critical period biological constraint (Moyer, 1999; Bongaerts et al., 1995; Young-Scholten, 2002).
Deaf and feral children
Cases of deaf and feral children provide evidence for a biologically determined CP for L1. Feral children are those not exposed to language in infancy/childhood due to being brought up in the wild, in isolation and/or confinement. A classic example is 'Genie', who was deprived of social interaction from birth until discovered aged thirteen (post-pubescent). She was completely without language, and after seven years of rehabilitation still lacked linguistic competence. Another case is ‘Isabelle’, who was incarcerated with her deaf-mute mother until the age of six and a half (pre-pubescent). She also had no language skills, but, unlike Genie, quickly acquired normal language abilities through systematic specialist training.
反对
While the window for learning a second language never completely closes, certain linguistic aspects appear to be more affected by the age of the learner than others. For example, adult second-language learners nearly always retain an immediately identifiable foreign accent, including some who display perfect grammar (Oyama 1976).
反对者们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 period has ended, a window of opportunity suddenly closed. Theo Bongaerts takes a very different approach in his paper, which again f
ocusses 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!
支持
The concept of a critical period is well known in nature. One example is imprinting in ducks and geese, where it is claimed that ducklings and goslings can be induced to adopt chickens, people, or even mechanical objects as their mothers if they encounter them within a certain short period after hatching. In humans, on the basis of extant evidence, it seems that there is a critical period for first language acquisition; those unfortunate persons who are not exposed to any language before puberty seem unable to properly acquire the syntax of their first language later in life.