The influence of age, experience and native-language phonology on second-language speech perception and production

The main objective of this study was to investigate possible reasons why younger second-language (L2) learners are often more successful than adults in L2 speech processing. One explanation, the Category Expansion Hypothesis, holds that first language (L1) sounds become better defined with age, so that uncommitted perceptual space becomes more and more committed to L1 sounds (Flege, 1992). This study examined whether younger L2 learners, whose L1 sound systems are still developing, are less likely than older L2 learners to associate L2 and L1 sounds, enabling them to eventually perceive and produce L2 sounds more accurately than adults.; To test the claim that children rather than adults are less likely to associate L2 with L1 sounds, in Experiment 1 beginning child (8–9 years), teen (12–13 years) and adult (20–21 years) Korean-English bilinguals judged the similarity between English and Korean vowels. In addition age of L2 acquisition-matched participants who had been exposed to English for five years also participated. Results of this experiment revealed that the younger beginning L2 learners were in fact less likely than adults to identify English sounds with Korean sounds.; Next, to test the claim that judgments of cross-language similarity predict L2 perception/production abilities for children and adults alike, in Experiments 2 and 3 both the beginning and advanced Korean-English bilinguals performed English vowel discrimination and production tasks. Results indicated that judgments of cross-language similarity, as shown in Experiment 1, predicted the ability to perceive and produce sounds in the second language. Indeed, children, who were less likely to perceptually associate L2 sounds with L1 sounds, displayed a superior ability to produce L2 sounds both at beginning and more advanced levels, suggesting that L2 speech learning in childhood is less constrained by L1 phonology. In contrast, adults' perception/production skills were determined by the degree of L1-L2 perceptual similarity, implicating long-lasting effects of native-language phonology on adult L2 speech learning. These findings support the Category Expansion Hypothesis and lend evidence that child learners' superior attainment in L2 speech learning may indeed reflect the developmental state of the L1 sound system at the time of L2 learning.