The final lengthening of pre-boundary syllables turns into final shortening as boundary strength levels increase

Phrase-final syllable duration and pauses are generally considered to be positively correlated: The stronger the boundary, the longer the duration of phrase-final syllables, and the more likely or longer a pause. Exploring a large sample of complex literary prose texts read aloud, we examined pause likelihood and duration, pre-boundary syllable duration, and the pitch excursion at prosodic boundaries. Comparing these features across six predicted levels of boundary strength (level 0: no break; 1: simple phrase break; 2: short comma phrase break; 3: long comma phrase break; 4: sentence boundary; 5: direct speech boundary), we find that they are not correlated in a simple monotonic fashion. Whereas pause duration monotonically increases with boundary strength, both pre-boundary syllable duration and the pitch excursion on the pre-boundary syllable are largest for level-2 breaks and decrease significantly through levels 3 to 5. Our analysis suggests that pre-boundary syllable duration is partly contingent on the tonal realization, which is subject to f0 declination as the utterance progresses. We also surmise that pre-boundary syllable duration reflects differences in planning complexity for the different prosodic and syntactic boundaries. Overall, this study shows that a simple monotonic correlation between pause duration and pre-boundary syllable duration is not valid.