Audibility of American English vowels produced by English-, Chinese-, and Korean-native speakers in long-term speech-shaped noise

The purpose of this study was to evaluate whether there were significant differences in audibility of American English vowels in noise produced by non-native and native speakers. Detection thresholds for 12 English vowels with equalized durations of 170 ms produced by 10 English-, Chinese- and Korean-native speakers were measured for young normal-hearing English-native listeners in the presence of speech-shaped noise presented at 70 dB SPL. Similar patterns of vowel detection thresholds as a function of the vowel category were found for native and non-native speakers, with the highest thresholds for /u/ and /?/ and lowest thresholds for /i/ and /e/. In addition, vowel detection thresholds for non-native speakers were significantly lower and showed greater speaker variability than those for native speakers. Thresholds for vowel detection predicted from an excitation-pattern model corresponded well to behavioral thresholds, implying that vowel detection was primarily determined by the vowel spectrum regardless of speaker language background. Both behavioral and predicted thresholds showed that vowel audibility was similar or even better for non-native speakers than for native speakers, indicating that vowel audibility did not account for non-native speakers' lower-than-native intelligibility in noise. Effects of non-native speakers' English proficiency level on vowel audibility are discussed.