The tongue and lips in Lombard speech: A pilot study of vowel-space expansion

Abstract

We investigate some ways in which speech production alters to make speech sounds more intelligible to a listener. This single speaker pilot study uses ultrasound tongue imaging and videos of lips to investigate the underlying articulatory processes used to distinguish six different monophthongal vowels in Scottish English in a consistent b__p frame. Lombard speech was elicited in an interactive feedback task with a neutral condition and a condition where the listener's hearing was masked by speech babble. As a baseline, the acoustic formant space was measured, which showed Lombard effects of F1 lowering for all vowels except /i/ and an increase in intensity. In articulation, we found that in the low and back vowel targets, the hyper-articulated version has extra lowering. However, for high front vowels /i/ and /e/, the hyper-articulated version has slight blade lowering and dorsal retraction in association with raising into the palate. The vowel // has very little change, but seems to fit in the high front set. Lip protrusion and spreading are enhanced, appropriately. Despite the frame being identical in each word, qualitatively the speaker enhanced the /b/ but not the /p/, supporting models in which a CV unit is planned holistically in speech production.