Intonational structure mediates speech rate normalization in the perception of segmental categories

The question of if and to what extent listeners’ perceptual phonetic categories are sensitive to prosodically driven variability has been a topic of interest in the literature. The present study reports on two experiments which address this question in light of recent research. In Experiment 1, listeners categorized a VOT continuum as /p/ or /b/ in a target syllable (/pɑ/ or /bɑ/). The target was placed in a carrier phrase where the duration and f0 of the pre-target syllable were manipulated. Results suggest listeners are sensitive to intonational structure in their computation of speech rate, interpreting a short syllable with low-rising f0 (created from an L-H% boundary tone in English intonational phonology) as an increase in speech rate. This perceived increase in rate shifts the category boundary of the subsequent target VOT. Experiment 2 showed listeners similarly adjusted categorization of a vowel duration continuum, where vowel duration is a cue to a following obstruent’s voicing (categorized as “coat” or “code”). Taken together, these results suggest that listeners are sensitive to intonational structure in their perception of segmental contrasts and use the distribution of tonal targets over a given temporal interval in computing speech rate.