Intelligibility of speech produced by sighted and blind adults.

PURPOSE: It is well known that speech uses both the auditory and visual modalities to convey information. In cases of congenital sensory deprivation, the feedback language learners have access to for mapping visible and invisible orofacial articulation is impoverished. Although the effects of blindness on the movements of the lips, jaw, and tongue have been documented in francophone adults, not much is known about their consequences for speech intelligibility. The objective of this study is to investigate the effects of congenital visual deprivation on vowel intelligibility in adult speakers of Canadian French. METHOD: Twenty adult listeners performed two perceptual identification tasks in which vowels produced by congenitally blind adults and sighted adults were used as stimuli. The vowels were presented in the auditory, visual, and audiovisual modalities (experiment 1) and at different signal-to-noise ratios in the audiovisual modality (experiment 2). Correct identification scores were calculated. Sequential information analyses were also conducted to assess the amount of information transmitted to the listeners along the three vowel features of height, place of articulation, and rounding. RESULTS: The results showed that, although blind speakers did not differ from their sighted peers in the auditory modality, they had lower scores in the audiovisual and visual modalities. Some vowels produced by blind speakers are also less robust in noise than those produced by sighted speakers. CONCLUSION: Together, the results suggest that adult blind speakers have learned to adapt to their sensory loss so that they can successfully achieve intelligible vowel targets in non-noisy conditions but that they produce less intelligible speech in noisy conditions. Thus, the trade-off between visible (lips) and invisible (tongue) articulatory cues observed between vowels produced by blind and sighted speakers is not equivalent in terms of perceptual efficiency.

Visual Influence on Auditory Perception of Vowels by French-Speaking Children and Adults.

Audiovisual interaction in speech perception is well defined in adults. Despite the large body of evidence suggesting that children are also sensitive to visual input, very few empirical studies have been conducted. To further investigate whether visual inputs influence auditory perception of phonemes in preschoolers in the same way as in adults, we conducted an audiovisual identification test. The auditory stimuli (/e/-/ø/ continuum) were presented either in an auditory condition only or simultaneously with a visual presentation of the articulation of the vowel /e/ or /ø/. The results suggest that, although all participants experienced visual influence on auditory perception, substantial individual differences exist in the 5- to 6-year-old group. While additional work is required to confirm this hypothesis, we suggest that auditory and visual systems are developing at that age and that multisensory phonological categorization of the rounding contrast took place only in children whose sensory systems and sensorimotor representations were mature.

Phonetic Implementation of Prosodic Emphasis in Preschool-Aged Children and Adults: Probing the Development of Sensorimotor Speech Goals.

Objective We aimed to investigate the production of contrastive emphasis in French-speaking 4-year-olds and adults. Based on previous work, we predicted that, due to their immature motor control abilities, preschool-aged children would produce smaller articulatory differences between emphasized and neutral syllables than adults. Method Ten 4-year-old children and 10 adult French speakers were recorded while repeating /bib/, /bub/, and /bab/ sequences in neutral and contrastive emphasis conditions. Synchronous recordings of tongue movements, lip and jaw positions, and speech signals were made. Lip positions and tongue shapes were analyzed; formant frequencies, amplitude, fundamental frequency, and duration were extracted from the acoustic signals; and between-vowel contrasts were calculated. Results Emphasized vowels were higher in pitch, intensity, and duration than their neutral counterparts in all participants. However, the effect of contrastive emphasis on lip position was smaller in children. Prosody did not affect tongue position in children, whereas it did in adults. As a result, children's productions were perceived less accurately than those of adults. Conclusion These findings suggest that 4-year-old children have not yet learned to produce hypoarticulated forms of phonemic goals to allow them to successfully contrast syllables and enhance prosodic saliency.

Speakers are able to categorize vowels based on tongue somatosensation.

Auditory speech perception enables listeners to access phonological categories from speech sounds. During speech production and speech motor learning, speakers' experience matched auditory and somatosensory input. Accordingly, access to phonetic units might also be provided by somatosensory information. The present study assessed whether humans can identify vowels using somatosensory feedback, without auditory feedback. A tongue-positioning task was used in which participants were required to achieve different tongue postures within the /e, ε, a/ articulatory range, in a procedure that was totally nonspeech like, involving distorted visual feedback of tongue shape. Tongue postures were measured using electromagnetic articulography. At the end of each tongue-positioning trial, subjects were required to whisper the corresponding vocal tract configuration with masked auditory feedback and to identify the vowel associated with the reached tongue posture. Masked auditory feedback ensured that vowel categorization was based on somatosensory feedback rather than auditory feedback. A separate group of subjects was required to auditorily classify the whispered sounds. In addition, we modeled the link between vowel categories and tongue postures in normal speech production with a Bayesian classifier based on the tongue postures recorded from the same speakers for several repetitions of the /e, ε, a/ vowels during a separate speech production task. Overall, our results indicate that vowel categorization is possible with somatosensory feedback alone, with an accuracy that is similar to the accuracy of the auditory perception of whispered sounds, and in congruence with normal speech articulation, as accounted for by the Bayesian classifier.

Impact of visual and auditory deprivation on speech perception and production in adults.

Speech perception relies on auditory and visual cues and there are strong links between speech perception and production. We aimed to evaluate the role of auditory and visual modalities on speech perception and production in adults with impaired hearing or sight versus those with normal hearing and sight. We examined speech perception and production of three isolated vowels (/i/, /y/, /u/), which were selected based on their different auditory and visual perceptual saliencies, in 12 deaf adults who used one or two cochlear implants (CIs), 14 congenitally blind adults, and 16 adults with normal sight and hearing. The results showed that the deaf adults who used a CI had worse vowel identification and discrimination perception and they also produced vowels that were less typical or precise than other participants. They had different tongue positions in speech production, which possibly partly explains the poorer quality of their spoken vowels. Blind individuals had larger lip openings and smaller lip protrusions for the rounded vowel and unrounded vowels, compared to the other participants, but they still produced vowels that were similar to those produced by the adults with normal sight and hearing. In summary, the deaf adults, even though they used CIs, had greater difficulty in producing accurate vowel targets than the blind adults, whereas the blind adults were still able to produce accurate vowel targets, even though they used different articulatory strategies.

Auditory and Somatosensory Interaction in Speech Perception in Children and Adults.

Multisensory integration (MSI) allows us to link sensory cues from multiple sources and plays a crucial role in speech development. However, it is not clear whether humans have an innate ability or whether repeated sensory input while the brain is maturing leads to efficient integration of sensory information in speech. We investigated the integration of auditory and somatosensory information in speech processing in a bimodal perceptual task in 15 young adults (age 19-30) and 14 children (age 5-6). The participants were asked to identify if the perceived target was the sound /e/ or /ø/. Half of the stimuli were presented under a unimodal condition with only auditory input. The other stimuli were presented under a bimodal condition with both auditory input and somatosensory input consisting of facial skin stretches provided by a robotic device, which mimics the articulation of the vowel /e/. The results indicate that the effect of somatosensory information on sound categorization was larger in adults than in children. This suggests that integration of auditory and somatosensory information evolves throughout the course of development.

Vowel intelligibility in children with cochlear implants: An acoustic and articulatory study.

In child cochlear implant (CI) users, early implantation generally results in highly intelligible speech. However, for some children developing a high level of speech intelligibility may be problematic. Studies of speech production in CI users have principally been based on perceptual judgment and acoustic measures. Articulatory measures, such as those collected using ultrasound provide the opportunity to more precisely evaluate what makes child CI users more intelligible. This study investigates speech production and intelligibility in children with CI using acoustic and articulatory measures. Ten children with unilateral or bilateral CIs and 13 children with normal hearing (NH) participated in the study. Participants repeated five English vowels (/a/, /e/, /i/, /o/, /u/) with and without auditory feedback. Ultrasound was used to capture tongue positions and acoustic signals were recorded simultaneously. The results showed that, despite quite similar acoustic results, the two speaker groups made different use of the tongue to implement vowel contrasts. Indeed, the tongue position was lower in the feedback OFF condition than the feedback ON condition for all participants, but the magnitude of this difference was larger for CI users than for their NH peers. This difference led to diminished intelligibility scores for CI users. This study shows the limitation of acoustic measurements alone and demonstrates how the use of articulatory measurements can explain intelligibility patterns. Moreover, our results show that when cochlear implantation occurs early in life and auditory feedback is available, CI users' intelligibility is comparable to that of their NH peers.

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

This study investigated the effects of visual deprivation on the relationship between speech perception and production by examining compensatory responses to real-time perturbations in auditory feedback. Specifically, acoustic and articulatory data were recorded while sighted and congenitally blind French speakers produced several repetitions of the vowel /ø/. At the acoustic level, blind speakers produced larger compensatory responses to altered vowels than their sighted peers. At the articulatory level, blind speakers also produced larger displacements of the upper lip, the tongue tip, and the tongue dorsum in compensatory responses. These findings suggest that blind speakers tolerate less discrepancy between actual and expected auditory feedback than sighted speakers. The study also suggests that sighted speakers have acquired more constrained somatosensory goals through the influence of visual cues perceived in face-to-face conversation, leading them to tolerate less discrepancy between expected and altered articulatory positions compared to blind speakers and thus resulting in smaller observed compensatory responses.

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

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.

Effects of blindness on production-perception relationships: Compensation strategies for a lip-tube perturbation of the French [u].

The impact of congenital visual deprivation on speech production in adults was examined in an ultrasound study of compensation strategies for lip-tube perturbation. Acoustic and articulatory analyses of the rounded vowel /u/ produced by 12 congenitally blind adult French speakers and 11 sighted adult French speakers were conducted under two conditions: normal and perturbed (with a 25-mm diameter tube inserted between the lips). Vowels were produced with auditory feedback and without auditory feedback (masked noise) to evaluate the extent to which both groups relied on this type of feedback to control speech movements. The acoustic analyses revealed that all participants mainly altered F2 and F0 and, to a lesser extent, F1 in the perturbed condition - only when auditory feedback was available. There were group differences in the articulatory strategies recruited to compensate; while all speakers moved their tongues more backward in the perturbed condition, blind speakers modified tongue-shape parameters to a greater extent than sighted speakers.

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

OBJECTIVES: The effects of increased speaking rates on vowels have been well documented in sighted adults. It has been reported that in fast speech, vowels are less widely spaced acoustically than in their citation form. Vowel space compression has also been reported in congenitally blind speakers. The objective of the study was to investigate the interaction of vision and speaking rate in adult speakers. PATIENTS AND METHODS: Contrast distances between vowels were examined in conversational and fast speech produced by 10 congenitally blind and 10 sighted French-Canadian adults. Acoustic analyses were carried out. RESULTS: Compared with the sighted speakers, in the fast speaking condition, the blind speakers produced more vowels with contrast along the height, place of articulation, and rounding features located within the auditory target regions typical of French vowels. CONCLUSION: Blind speakers relied more heavily than sighted speakers on auditory properties of vowels to maintain perceptual distinctiveness.

Exploring consequences of short- and long-term deafness on speech production: a lip-tube perturbation study.

Studies have reported strong links between speech production and perception. We aimed to evaluate the role of long- and short-term auditory feedback alteration on speech production. Eleven adults with normal hearing (controls) and 17 cochlear implant (CI) users (7 pre-lingually deaf and 10 post-lingually deaf adults) were recruited. Short-term auditory feedback deprivation was induced by turning off the CI or by providing masking noise. Acoustic and articulatory measures were obtained during the production of /u/, with and without a tube inserted between the lips (perturbation), and with and without auditory feedback. F1 values were significantly different between the implant OFF and ON conditions for the pre-lingually deaf participants. In the absence of auditory feedback, the pre-lingually deaf participants moved the tongue more forward. Thus, a lack of normal auditory experience of speech may affect the internal representation of a vowel.