Non-native durational patterns decrease speech intelligibility

In native speech, durational patterns convey linguistically relevant phenomena such as phrase structure, lexical stress, rhythm, and word boundaries. The lower intelligibility of non-native speech may be partly due to its deviant durational patterns. The present study aims to quantify the relative contributions of non-native durational patterns and of non-native speech sounds to intelligibility. In a Speech Reception Threshold study, duration patterns were transplanted between native and non-native versions of Dutch sentences. Results for non-transplanted, original versions show that intelligibility thresholds (critical speech-to-noise ratios) differed by about 4 dB between native and non-native versions. Results for manipulated versions with transplanted durations indicate that about 0.4 to 1.1 dB of this difference was due to the durational patterns, and that this contribution was larger if the native and non-native patterns were more deviant. The remainder of the difference must have been due to non-native speech sounds in these materials. This finding supports recommendations to attend to durational patterns as well as native-like speech sounds, when learning to speak a foreign language.