Speaking Clearly for the Blind: Acoustic and Articulatory Correlates of Speaking Conditions in Sighted and Congenitally Blind Speakers

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.

Compensations to auditory feedback perturbations in congenitally blind and sighted speakers: Acoustic and articulatory data

“…In another study that compared sighted and blind speakers, we used the paradigm of lip perturbation to investigate the extent to which visual deprivation affects articulatory compensations [ 13 ]. Ultrasound imaging was used to measure tongue shape and position when producing the vowel /u/ before, during, and after the insertion of a lip tube.…”

Maintaining Distinctiveness at Increased Speaking Rates: A Comparison between Congenitally Blind and Sighted Speakers

“…The study showed that the size of the vowel space, calculated by the average of the Euclidean distances in the mel-transformed formant space, was significantly smaller than that of age-matched sighted speakers. In a follow-up study, speakers were asked to produce vowels in carrier sentences in 2 speaking conditions: clear speech and conversational speech [3]. In the clear speech condition, more weight was given to intelligibility requirements, causing speakers to produce vowels and consonants with longer duration and/or hyperarticulated gestures.…”

Visual Speech Perception Cues Constrain Patterns of Articulatory Variation and Sound Change

“…In contexts where perceptual demands are high, speakers are predicted to prefer round variants of /ɔ/, given that the addition of visible lip rounding enhances the contrast with /ɑ/. This prediction is supported by the findings of Ménard et al ( 2016 ), who show that sighted speakers consider how their speech will be perceived both visually and auditorily, and increase the degree of lip rounding for /u/ in clear speech. The integration of visual speech cues may therefore offer an explanation for the finding of Harrington et al ( 2011 ) that British English /u/ has retained its rounding as it has undergone fronting: in acoustic terms, both [y] and [ɨ] should be viable articulations for fronted /u/, but visibly round [y] is predicted to maintain a stronger contrast with /i/.…”

“…More recently, a series of studies by Ménard et al ( 2009 , 2013 , 2015 , 2016 ) has demonstrated the importance of audiovisual perception to speech intelligibility through an investigation of differences in the use of visible articulation by sighted and congenitally blind speakers. Ménard et al ( 2009 ), for instance, tested the production and discrimination of vowel contrasts among sighted and blind speakers of Canadian French.…”

“…They find that blind speakers exhibit greater auditory discrimination abilities than sighted speakers, but that sighted speakers have a significantly larger vowel space, suggesting that the availability of visual speech cues (or lack thereof) influences speakers' production targets. Ménard et al ( 2015 , 2016 ) find that in producing clear speech, only sighted speakers produce more pronounced lip movements, while blind speakers rely on changes in tongue movement. Thus, when attempting to enhance speech intelligibility, sighted speakers seem to consider how their speech will be perceived not only auditorily, but also visually.…”