Abstract
Compared to conversational speech, clear speech is produced with longer vowel duration, greater intensity, increased contrasts between vowel categories, and decreased dispersion within vowel categories. Those acoustic correlates are produced by larger movements of the orofacial articulators, including visible (lips) and invisible (tongue) articulators. Thus, clear speech provides the listener with audible and visual cues that are used to increase the overall intelligibility of speech produced by the speaker. It is unclear how those cues are produced by visually impaired speakers who never had access to vision. In this paper, we investigate the acoustic and articulatory correlates of vowels in clear versus conversational speech, and in sighted and congenitally blind speakers. Participants were recorded using electroarticulography while producing multiple repetitions of the ten Quebec French oral vowels in carrier sentences in both speaking conditions. Articulatory variables (lip, jaw, and tongue positions) as well as acoustic variables (contrasts between vowels, within-vowel dispersion, pitch, duration, and intensity) were measured. Lip movements were larger when going from conversational to clear speech in sighted speakers only. On the other hand, tongue movements were affected to a larger extent in blind speakers compared to their sighted peers. These findings confirm that vision plays an important role in the maintenance of speech intelligibility.
Highlights
Clear speech versus conversational speechSpeech production can be thought of as a trade-off between two competing constraints: the need to ensure intelligibility and the tendency to expend minimal effort [1,2,3]
We had four hypotheses: 1) compared to conversational speech, speech produced in the clear speech condition would be associated with longer duration, larger acoustic contrasts between vowels, and tighter acoustic clustering within vowel categories; 2) at the articulatory level, clear speech would be produced by larger tongue, lip, and jaw displacements compared to conversational speech; 3) sighted speakers would increase visible lip gestures to a greater extent than blind speakers when going from conversational to clear speech; and 4) tongue displacement would be larger in blind speakers than in sighted speakers in clear speech compared to conversational speech
The analysis showed a significant main effect of speaking condition on contrast distance (F(1,18) = 20.85; p
Summary
Speech production can be thought of as a trade-off between two competing constraints: the need to ensure intelligibility and the tendency to expend minimal effort [1,2,3]. Sighted speakers had reduced displacements of the tongue when going from the neutral to the focused conditions, whereas blind speakers had significantly larger differences in tongue displacements for the two prosodic conditions These studies suggest that there is a trade-off between displacements of the lips (visible articulators) and of the tongue (invisible articulator), which is regulated by vision. We investigate another perceptual enhancement condition, namely clear speech, in sighted and congenitally blind adult speakers of French This condition is known to be driven by global intelligibility demands (on the domain of the entire speech sequences) as opposed to contrastive focus, in which intelligibility demands are increased locally (on a specific word, for instance). We had four hypotheses: 1) compared to conversational speech, speech produced in the clear speech condition would be associated with longer duration, larger acoustic contrasts between vowels, and tighter acoustic clustering within vowel categories; 2) at the articulatory level, clear speech would be produced by larger tongue, lip, and jaw displacements compared to conversational speech; 3) sighted speakers would increase visible lip gestures to a greater extent than blind speakers when going from conversational to clear speech; and 4) tongue displacement would be larger in blind speakers than in sighted speakers in clear speech compared to conversational speech
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