Factors influencing ratios of filled pauses at clause boundaries in Japanese

Speech disfluencies have been studied as clues to human speech production mechanisms. Major constituents are assumed to be principal units of planning and disfluencies are claimed to occur when speakers have some trouble in planning such units. We tested two hypotheses about the probability of disfluencies by examining the ratios of filled pauses (fillers) at sentence and clause boundaries: 1) the deeper the boundary, the higher the ratio of filled pauses (the boundary hypothesis); 2) the more complex the upcoming constituent, the higher the ratio of filled pauses (the complexity hypothesis). The both hypotheses were supported by filler ratios at clause boundaries, but not by those at sentence boundaries. The results are discussed in light of speech production models.