Confusability in L2 vowels: analyzing the role of different features

The production and perception of L2 vowels are influenced by the L1 vowel system. Most studies on L2 vowel production evaluate the learners’ pronunciation using subjective listening tests. In this study we present a novel objective method for investigating learner vowel confusability based on acoustic measurements. Monosyllabic words uttered by Spanish learners of Dutch are analyzed, and basic acoustic features – formant frequencies and duration – are extracted. Native Dutch speakers’ measurements are used to obtain models for the Dutch vowels, which are employed to compute likelihood ratios and similarity distributions of the Spanish realizations in comparison to the Dutch target vowels. The likelihood ratios are presented in a matrix format similar to a confusion matrix crossing the target vowels by the vowels as classified. Results based on spectral features alone confirm the existence of an attractor effect of L1 vowels on L2 vowels. Overall, including duration in the analyses decreases the number of confusions. Comparing the confusion values on different feature sets helps analyzing the impact of the specific features. The results of the present study suggest that although the Spanish learners’ use of duration is not native-like, it does help reduce confusability among Dutch vowels.