Intonation mediates speech rate normalization in the perception of segmental categories
This thesis reports on two experiments that address the question of how listeners are sensitive to prosodic/intonational structure in their perception of segmental contrasts. 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 (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.