The perception and production of nonnative phones in second language (L2) learners can be improved via auditory training, but L2 learning is often characterized by large differences in performance across individuals. This study examined whether success in learning L2 vowels, via five sessions of high-variability phonetic training, related to the learners' native (L1) vowel processing ability or their frequency discrimination acuity. A group of native speakers of Greek received training, while another completed the pre-/post-tests but without training. Pre-/post-tests assessed different aspects of their L2 and L1 vowel processing and frequency acuity. L2 and L1 vowel processing were assessed via: (a) Natural English (L2) vowel identification in quiet and in multi-talker babble, and natural Greek (L1) vowel identification in babble; (b) the categorization of synthetic English and Greek vowel continua; and (c) discrimination of the same continua. Frequency discrimination acuity was assessed for a nonspeech continuum. Frequency discrimination acuity was related to measures of both L1 and L2 vowel processing, a finding that favors an auditory processing over a speech-specific explanation for individual variability in L2 vowel learning. The most efficient frequency discriminators at pre-test were also the most accurate both in English vowel perception and production after training.

This study examined the extent to which previous experience with duration in first language (L1) vowel distinctions affects the use of duration when perceiving vowels in a second language (L2). Native speakers of Greek (where duration is not used to differentiate vowels) and Japanese (where vowels are distinguished by duration) first identified and rated the eleven English monophthongs, embedded in /bVb/ and /bVp/ contexts, in terms of their L1 categories and then carried out discrimination tests on those English vowels. The results demonstrated that both L2 groups were sensitive to durational cues when perceiving the English vowels. However, listeners were found to temporally assimilate L2 vowels to L1 category/categories. Temporal information was available in discrimination only when the listeners’ L1 duration category/categories did not interfere with the target duration categories and hence the use of duration in such cases cannot be attributed to its perceptual salience as has been proposed.

To become fluent in a second language, learners need to acquire a large vocabulary. However, the cognitive and affective mechanisms that support word learning, particularly among second language learners, are only beginning to be understood. Prior research has focused on intentional learning and small artificial lexicons. In the current study investigating the sources of individual variability in word learning and their underlying mechanisms, participants intentionally and incidentally learned a large vocabulary of Welsh words (i.e., emulating word learning in the wild) and completed a large battery of cognitive and affective measures. The results showed that, for both learning conditions, native language knowledge, auditory/phonological abilities and orthographic sensitivity all made unique contributions to word learning. Importantly, short-term/working memory played a significantly larger role in intentional learning. We discuss these results in the context of the mechanisms that support both native and non-native language learning.

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