Audiovisual enhancement of vowel contrast: Production and perception of the cot-caught contrast in Chicago

Abstract

<p>This paper argues that vowel systems are organized not only around principles of auditory-acoustic dispersion, but also around non-auditory perceptual factors, specifically vision. A series of experiments investigate production and perception of the cot-caught contrast by speakers from Chicago, where /ɑ/ and /ɔ/ have been influenced by the Northern Cities Shift. Experiment 1 presents an acoustic and articulatory analysis of vowel production using ultrasound tongue imaging and lip video. All speakers who retain the /ɑ/-/ɔ/ are shown to contrast distinguish /ɔ/ from /ɑ/ through lip rounding, while the lingual distinction may be weak or absent. In Experiment 2, participants were observed to produce hyperarticulated labial gestures in a corrective focus task; in some cases, hyperarticulated lip gestures occur in the absence of a corresponding increase in acoustic distance between /ɑ/ and /ɔ/, suggesting that lip rounding enhancement is not purely a byproduct of auditory enhancement. Experiment 3 demonstrates that visible lip gestures enhance perceptibility of the cot-caught contrast, such that visibly round variants of /ɔ/ are perceptually more robust than unround variants. These results suggest that speakers and listeners prefer articulatory strategies that provide contrast in both the auditory and visual domains, as opposed to contrast in the auditory domain alone.<br></p>