Effects of surprisal and boundary strength on phrase-final lengthening

Abstract

This study examines the influence of prosodic structure (pitch accents and boundary strength) and information density (ID) on phrase-final syllable duration. Phrase-final syllable durations and following pause durations were measured in a subset of a German radio-news corpus (DIRNDL), consisting of about 5 hours of manually annotated speech. The prosodic annotation is in accordance with the autosegmental intonation model and includes labels for pitch accents and boundary tones. We treated pause duration as a quantitative proxy for boundary strength. ID was calculated as the surprisal of the syllable trigram of the preceding context, based on language models trained on the DeWaC corpus. We found a significant positive correlation between surprisal and phrase-final syllable duration. Syllable duration was statistically modeled as a function of prosodic factors (pitch accent and boundary strength) and surprisal in linear mixed effects models. The results revealed an interaction of surprisal and boundary strength with respect to phrase-final syllable duration. Syllables with high surprisal values are longer before stronger boundaries, whereas low-surprisal syllables are longer before weaker boundaries. This modulation of pre-boundary syllable duration is observed above and beyond the well-established phrase-final lengthening effect.