Native and non-native clear speech production.

Abstract

Previous work established that both native and non-native clear speech increase intelligibility for native and proficient non-native listeners. However, non-native clear speech enhanced intelligibility less than native clear speech. In this study, we examine native and non-native conversational and clear speech productions with an eye on the differences in hyperarticulation strategies that may underlie a smaller clear speech intelligibility benefit. Results revealed a slower conversational speaking rate for non-native talkers compared with native talkers. Clear speaking rate was similar for both groups suggesting a limit in the speaking rate decrease in intelligibility enhancing clear speech. The durational distinction between tense and lax vowels was increased less in non-native speech due to the smaller speaking rate decrease in clear speech. Analyses of the stop voice onset time (VOT) showed that non-native talkers lengthened the voiced category in the negative VOT direction, while the voiceless category was lengthened less in clear speech. Finally, examination of vowel space expansion in clear speech revealed differences between the two talker groups reflecting non-native talkers’ inexperience in producing some of the vowel targets. Combined, these results suggest that a complex interaction of articulatory difficulty, proficiency, and native language background determines levels of non-native clear speech intelligibility.