How are second language phoneme contrasts learned

Abstract

Listeners are sensitive to phonetic differences that correspond to phonemic contrasts in their native language, and they often exhibit difficulty discriminating sounds that are not contrastive in their native language. Although a large literature shows that learners can improve their perception of novel contrasts with exposure to a second language, there is still little understanding of how learners accomplish this. There are at least two possible sources of evidence that learners might use to acquire sensitivity to novel sound contrasts. First, learners might use their knowledge of minimal pairs in the language to determine which sounds are contrastive. For example, knowing the minimal pair toe-doe may provide learners with evidence that /t/ and /d/ are contrastive in English (Lexical-Contrast-Based Evidence). Second, learners might compute the statistical distributions of the acoustic-phonetic properties of their second language input. The logic is that two contrastive speech sounds will be represented by distinct distributions along a of a number of acoustic-phonetic dimensions (Distribution-Based Evidence). Although both are possible sources of the evidence learners use to acquire novel second language sound contrasts, the relative influence of these two types of information is not yet known. Experiments 1 and 2 of this dissertation employ a variety of training techniques to determine the relative influence of Lexical-Contrast-Based and Distribution-Based evidence on participants' sensitivity to a novel contrast. Results indicate that while both kinds of evidence affect sensitivity, Lexical-Contrast-Based evidence had a stronger influence on discrimination performance. While Experiments 1 and 2 tested learners' sensitivity to novel contrasts, it is not yet clear that improved discrimination ability is of benefit in subsequent second language learning. Experiment 3 examined the linguistic relevance of participants' improved discrimination ability by testing learners' lexical representations for new words that differed minimally with respect to the trained contrast. Regardless of training condition, participants did not record the new contrast distinctly in their lexical representations. That participants exhibited sensitivity to the novel contrast but were nonetheless unable to record the contrast lexically suggests a dissociation between learners' acoustic-phonetic knowledge of their second language and their ability to represent that knowledge contrastively in their lexicon.