A moving target? Comparing within-talker variability in vowel production between native and non-native English speakers across two speech styles

Non-native English speakers may show greater variability in speech production than native talkers due to differences in their developing representations of second-language speech targets. Few studies have compared within-talker variability in speech production between native and non-native speakers. In the present study, vowels produced by four monolingual English speakers and four later learners of English as a second language (Spanish L1) were compared. Five repetitions of six target syllables (“bead, bid, bayed, bed, bad” and “bod”), produced in conversational and clear speech styles, were analyzed acoustically. Fundamental and formant frequencies were measured at 20, 50 and 80% of vowel duration. Standard deviations computed across the five repetitions of each vowel were compared across speaking styles and talker groups. Preliminary data analyses indicate greater within-talker variability for non-native than native talkers. Non-native talkers’ within-talker variability also increased from conversational to clear speech for most measures. For some native talkers, within-talker variability was smaller for vowels with near neighbors in the vowel space than for vowels with more spectrally distant neighbors. This correlation was stronger in clear speech for talkers who showed a significant clear-speech intelligibility benefit in production in a related study. Implications for theories of vowel production will be discussed.