Discourse structure and its influence on local speech rate

This paper regards the methodological question of how to account for local variations in speech rate that are probably caused by structural aspects of the discourse. The present study is part of a larger research project on the acoustic determinants of information structure in spontaneous and read discourse in Dutch. In order to understand the various contributions that play a role in the temporal course of a spoken discourse, we measured variation in syllable duration per interpausal speech run. Our speech material consisted of a retold story as produced by 4 male and 4 female Dutch speakers. In a pilot approach we tried to normalize syllable duration for phonotactic differences, and for lengthening caused by stress. Although more sophisticated methods will be applied in the near future, our first results indicate that there is a large variability in average syllable duration over the various interpausal speech runs for each of the eight speakers. No straightforward relation is found between the number of syllables within a run and the average syllable duration. After normalization the remaining temporal variations are related to the struc­ ture of the discourse: slowing down at the start of a new paragraph and speeding up at the end of a paragraph and in personal comments and additions. Apart from studying the variations in speech rate we also studied the different strategies that speakers applied in their use of pauses.