Timing relations in speech and the identification of voice-onset times: a stable perceptual boundary for voicing categories across speaking rates.

This study shows that the ratio of voice onset time (VOT) to syllable duration for /t/ and /d/ presents distributions with a stable boundary across speaking rates and that this boundary constitutes a perceptual criterion by which listeners judge the category affiliation of VOT. In Experiment 1, best-fit regression lines for VOT ratios of intervocalic /t/ and /d/ against speaking rate had zero slopes, and there was an inferable boundary between the distributions. In Experiment 2, listeners' identifications of syllable-initial stops conformed to this boundary ratio. In Experiment 3, VOT was held constant, while VOT ratios were altered by modifying the duration of the following vowel. As VOT ratios exceeded the boundary estimated from the data of Experiment 1, listeners' identifications shifted from /d/ to /t/. Timing relations in speech production can determine the identification of voicing categories across speaking rates.