Suprasegmental and segmental timing models in Mandarin Chinese and American English.

This paper formalizes and tests two key assumptions of the concept of suprasegmental timing: segmental independence and suprasegmental mediation. Segmental independence holds that the duration of a suprasegmental unit such as a syllable or foot is only minimally dependent on its segments. Suprasegmental mediation states that the duration of a segment is determined by the duration of its suprasegmental unit and its identity, but not directly by the specific prosodic context responsible for suprasegmental unit duration. Both assumptions are made by various versions of the isochrony hypothesis [I. Lehiste, J. Phonetics 5, 253-263 (1977)], and by the syllable timing hypothesis [W. Campbell, Speech Commun. 9, 57-62 (1990)]. The validity of these assumptions was studied using the syllable as suprasegmental unit in American English and Mandarin Chinese. To avoid unnatural timing patterns that might be induced when reading carrier phrase material, meaningful, nonrepetitive sentences were used with a wide range of lengths. Segmental independence was tested by measuring how the average duration of a syllable in a fixed prosodic context depends on its segmental composition. A strong association was found; in many cases the increase in average syllabic duration when one segment was substituted for another (e.g., bin versus pin) was the same as the difference in average duration between the two segments (i.e., [b] versus [p]). Thus, the [i] and [n] were not compressed to make room for the longer [p], which is inconsistent with segmental independence. Syllabic mediation was tested by measuring which locations in a syllable are most strongly affected by various contextual factors, including phrasal position, within-word position, tone, and lexical stress. Systematic differences were found between these factors in terms of the intrasyllabic locus of maximal effect. These and earlier results obtained by van Son and van Santen [R. J. J. H van Son and J. P. H. van Santen, "Modeling the interaction between factors affecting consonant duration," Proceedings Eurospeech-97, 1997, pp. 319-322] showing a three-way interaction between consonantal identity (coronals vs labials), within-word position of the syllable, and stress of surrounding vowels, imply that segmental duration cannot be predicted by compressing or elongating segments to fit into a predetermined syllabic time interval. In conclusion, while there is little doubt that suprasegmental units play important predictive and explanatory roles as phonological units, the concept of suprasegmental timing is less promising.