Effects of speaking rate on the behavior of tense and lax vowel durations

Abstract

The current study investigated the effects of speaking rate on the acoustic durations of four pairs of American English tense and lax vowels [i– i , æ–ε, ɑ–ʌ, u– u ] in four different postvocalic consonantal contexts [t, d, s, z] using seven subjects. Results showed that the durational behavior of tense and lax vowels as a function of rate was context dependent and followed one of two broad patterns: (i) in certain contexts (usually in /t/ and /z/ contexts), most of the tense–lax vowel pairs maintained a constant absolute duration difference across different rates, and (ii) in other contexts (usually /d/ and /s/) the change in tense vowel durations as a function of rate was significantly different from their lax vowel counterparts, so that the vowels maintained neither an absolute duration difference nor a constant proportional relationship. When the results were interpreted within the framework of several existing models of vowel duration, it was found that none of the models captured the durational behavior of these vowels as a function of rate. There was some support for the additive and imcompressibility models but none for the multiplicative model. This suggests a speech timing system that is more complex than the models suppose.