Intelligibility, fluency, and variability in non-native speech

Abstract

Native and non-native speech differ in many ways, including overall speech rate, which tends to be substantially slower for non-native speakers (Guion et al., 2000). Recent work has suggested that non-native speech may be not only slower, but also more variable when non-natives are reading aloud (Baese-Berk and Morrill, 2015). Speaking rate also influences how listeners perceive non-native speech—slower readers are perceived as more accented and less comprehensible (Munro and Derwing, 1998). In the present study, we ask whether variability in speaking rate also has this effect on listeners. Specifically, we ask whether speaking rate variability is correlated with non-native speaker intelligibility and/or with judgments of fluency. In the present study, we ask listeners to transcribe sentences from speakers who show more or less variability in speaking rate across sentences in a paragraph-length reading passage. We also ask them to rate the fluency of the read sentences. Speech samples were taken from native Mandarin, Korean and English speakers’ recordings of the English “North Wind and the Sun” passage in the ALLSSTAR collection of digital speech recordings (Bradlow et al., 2010). These results provide insight into the relationships between variability, intelligibility, and fluency in both native and non-native speech.