儿童-成人外语学习差异说.ppt

7.4 Explanations to Child and Adult L2 learning （儿童与成人外语学习差异原因说）;Explanations ;For explanations survey the differences between child and adult learners of second language from different perspectives and provide biological, cognitive and affective explanations for second language learning. ;In biological explanations for optimal age of L2 learning, the considerations are most prominent and influential .They are 1.the critical period hypothesis . 2.neurological considerations 3.psychomotor considerations;1)The critical period hypothesis;Definition of the critical period;During this period the brain retains plasticity, but with the onset of puberty this plasticity begins to disappear and learners seem to be relatively incapable of acquiring a native-like intonation and pronunciation of second language. Some research (Lenneberg 1976) suggests that this is the result of the lateralization（边化，偏侧性） of the language function in the left hemisphere of the brain. ;1.The critical period hypothesis is an inadequate account of the role played by age in SLA, because this assumption is only partially correct .pronunciation or accent is not the only criterion of successful L2 learning in term of success or rate of acquisition . As Ellis (1985)points out that the critical period hypothesis needs to be recast to account for why loss of plasticity affects pronunciation but not other levels of language .;2.Some psycholinguists raised doubts about “one single and unified critical period” hypothesis and proposed instead the “multi_critical period” hypothesis (Seliger 1978).They argued that process of the lateralization and localization of language function is a gradual one ,carrying on over many years. In general , the evidence linking cerebral dominance and age differences in learners in not clear yet . ;2) Neurological considerations;2.There is evidence in neurological research that as the human brain matures certain other functions to the right hemisphere. Language f