Multilevel modeling of between-speaker and within-speaker variation in spontaneous speech tempo

Speech tempo (articulation rate) varies both between and within speakers. The present study investigates several factors affecting tempo in a corpus of spoken Dutch, consisting of interviews with 160 high-school teachers. Speech tempo was observed for each phrase separately, and analyzed by means of multilevel modeling of the speaker's sex, age, country, and dialect region (between speakers) and length, sequential position of phrase, and autocorrelated tempo (within speakers). Results show that speech tempo in this corpus depends mainly on phrase length, due to anticipatory shortening, and on the speaker's country, with different speaking styles in The Netherlands (faster, less varied) and in Flanders (slower, more varied). Additional analyses showed that phrase length itself is shorter in The Netherlands than in Flanders, and decreases with speaker's age. Older speakers tend to vary their phrase length more (within speakers), perhaps due to their accumulated verbal proficiency.