Comprehensibility and the Acoustic Contrast Between Tense and Lax Vowels in Mandarin-Accented English Speech

This study investigates the relation between the comprehensibility of Mandarin-accented English speech and the degree of acoustic contrast in the vowel tenseness pairs [i] - [ɪ] and [u] - [ʊ]. We hypothesized that Mandarin speakers under-differentiate the tenseness vowel pairs and that variability in the acoustic contrast between tense and lax vowels correlates with variability in comprehensibility. Twenty Mandarin speakers and ten English speakers produced sentences with the target vowels, and 26 English speakers rated the sentences’ comprehensibility. We found that spectral difference between [u] - [ʊ] was relatively reduced in L2 speech and that L2 productions were overall more variable, compared to American speech. We also found that the degree of spectral contrast correlated with comprehensibility rating, suggesting that the degree of acoustic differentiation between phonological categories contributes to the comprehensibility of L2 speech.