Perceptual invariance of coarticulated vowels over variations in speaking rate

This study examined the perception and acoustics of a large corpus of vowels spoken in consonant-vowel-consonant syllables produced in citation-form (lists) and spoken in sentences at normal and rapid rates by a female adult. Listeners correctly categorized the speaking rate of sentence materials as normal or rapid (2% errors) but did not accurately classify the speaking rate of the syllables when they were excised from the sentences (25% errors). In contrast, listeners accurately identified the vowels produced in sentences spoken at both rates when presented the sentences and when presented the excised syllables blocked by speaking rate or randomized. Acoustical analysis showed that formant frequencies at syllable midpoint for vowels in sentence materials showed "target undershoot" relative to citation-form values, but little change over speech rate. Syllable durations varied systematically with vowel identity, speaking rate, and voicing of final consonant. Vowel-inherent-spectral-change was invariant in direction of change over rate and context for most vowels. The temporal location of maximum F1 frequency further differentiated spectrally adjacent lax and tense vowels. It was concluded that listeners were able to utilize these rate- and context-independent dynamic spectrotemporal parameters to identify coarticulated vowels, even when sentential information about speaking rate was not available.