Marginal Contrast Among Romanian Vowels: Evidence from ASR and Functional Load

This work quantifies the phonological contrast between the Romanian central vowels [2] and [1], which are considered separate phonemes, although they are historical allophones with few minimal pairs. We consider the vowels’ functional load within the Romanian inventory and the usefulness of the contrast for automatic speech recognition (ASR). Using a 7 hour corpus of automatically aligned broadcast speech, the relative frequencies of vowels are compared across phonological contexts. Results indicate a near complementary distribution of [2] and [1]: the contrast scores lowest of all pairwise comparisons on measures of functional load, and shows the highest Kullback-Leibler divergence, suggesting that few lexical distinctions depend on the contrast. Thereafter, forced alignment is performed using an existing ASR system. The system selects among [1], [2], ∅ for lexical /1/, testing for its reduction in continuous speech. The same data is transcribed using the ASR system where [2]/[1] are merged, testing the hypothesis that loss of a marginal contrast has little impact on ASR error rates. Both results are consistent with functional load calculations, indicating that the /2/ /1/ contrast is lexically and phonetically weak. These results show how automatic transcription tools can help test phonological predictions using continuous speech.