Deaf Speakers Research Articles

Topic-based variation as both cognitive and agentive

Abstract Topic-based style-shifting refers to the variation pattern that, when people talk about a topic, they shift to a linguistic style which is associated with the topic. Most of the research on topic-based variation in read speech have not taken stance-taking into consideration. This study argues that stance-taking needs to be included in the analysis of topic-based variation, for reading something aloud is a practice where individuals engage with the message communicated in a text. This study looks at the socially salient variable /ʂ/ in Taiwan Mandarin, and how deaf speakers exploit this variable to perform their stances towards a passage concerned with the political relationship between hearing people and deaf signers. The findings show that participants who demonstrate a stance of deaf solidarity diverge from standard speech styles in their repertoires when reading the deaf passage.

Individual variation in performing reading-aloud speech among deaf speakers

AbstractThe study examines the stylistic variation (interview vs. passage-reading) of socially meaningful variables among orally educated deaf speakers of Mandarin in Taipei, Taiwan. I examine the use of the retroflex and alveolar fricatives across two groups: deaf persons who received speech therapy or training, and those who did not receive speech medicalization. The two groups acquire the metalinguistic awareness of sibilant variation in different ways. Results show that the former group utilize the variables in the same way as hearing persons do – increasing the degree of retroflexion in reading-aloud speech. The latter group engage with the variable in an opposite way – decreasing the degree of retroflexion, which nevertheless also indexes able-bodiedness, possibly via the embodied link between a stronger hiss and a fronted sibilant. I argue that we need to carefully look at what different linguistic variants index through locating the variants in each speaker’s personal history.

Quantifying speech signal of deaf speakers with territory specific utterances to understand the acoustic characteristics

Hearing loss, deafness, hard of hearing and hearing impairment are the various terms used in the deaf community as a condition for inability to hear either partial or total impairment. The hearing loss in most of the deaf persons affects the language development to lead a normal life. The acoustic characteristic of deaf speaker is estimated in comparison with the normal speakers to create an assistive method. The speech signals are procured from the 32 territory-specific normal and deaf speakers by uttering ten Tamil words. The parameters analysed are pitch, formants, jitter and shimmer. From the overall results, it is observed that acoustic characteristics differ significantly for the deaf speakers and the quantitative values of the parameters are controlled by the normal speakers. Further the acoustic parameters may be used as a correction factor for the deaf speech signal such that the listeners can understand the deaf speech.

Quantifying speech signal of deaf speakers with territory specific utterances to understand the acoustic characteristics

Quantifying speech signal of deaf speakers with territory specific utterances to understand the acoustic characteristics

Analysis of Dravidian words uttered by deaf speakers using clustering techniques: deaf speech enhancement

A novel method for grouping the fundamental speech features of normal and deaf speakers using a new Modified Self Organising Map (M-SOM) clustering algorithm, and deaf speech enhancement using distance measure is presented. The M-SOM algorithm will automatically categorise the normal and deaf speaker speech features into two different clusters. Its performance is analysed in comparison with SOM and NMTF algorithms. The result obtained reveals that the M-SOM algorithm which is developed by combining the adaptive features of SOM and the Ward clustering methods provides lowest intra and highest inter-clustering and appears to be the best method for deaf speech signals. After clustering estimation of distance metric, termed as correction measure facilitates enhancement of the unclear deaf speech so that it could be understandable to normal speakers. Hence it can be inferred that the suggested method effectively enhances the deaf speech signal for better understanding by a normal listener.

Analysis of Dravidian words uttered by deaf speakers using clustering techniques: deaf speech enhancement

A novel method for grouping the fundamental speech features of normal and deaf speakers using a new Modified Self Organising Map (M-SOM) clustering algorithm, and deaf speech enhancement using distance measure is presented. The M-SOM algorithm will automatically categorise the normal and deaf speaker speech features into two different clusters. Its performance is analysed in comparison with SOM and NMTF algorithms. The result obtained reveals that the M-SOM algorithm which is developed by combining the adaptive features of SOM and the Ward clustering methods provides lowest intra and highest inter-clustering and appears to be the best method for deaf speech signals. After clustering estimation of distance metric, termed as correction measure facilitates enhancement of the unclear deaf speech so that it could be understandable to normal speakers. Hence it can be inferred that the suggested method effectively enhances the deaf speech signal for better understanding by a normal listener.

Analysis of Deaf Speakers’ Speech Signal for Understanding the Acoustic Characteristics by Territory Specific Utterances

An important concern with the deaf community is inability to hear partially or totally. This may affect the development of language during childhood, which limits their habitual existence. Consequently to facilitate such deaf speakers through certain assistive mechanism, an effort has been taken to understand the acoustic characteristics of deaf speakers by evaluating the territory specific utterances. Speech signals are acquired from 32 normal and 32 deaf speakers by uttering ten Indian native Tamil language words. The speech parameters like pitch, formants, signal-to-noise ratio, energy, intensity, jitter and shimmer are analyzed. From the results, it has been observed that the acoustic characteristics of deaf speakers differ significantly and their quantitative measure dominates the normal speakers for the words considered. The study also reveals that the informative part of speech in a normal and deaf speakers may be identified using the acoustic features. In addition, these attributes may be used for differential corrections of deaf speaker’s speech signal and facilitate listeners to understand the conveyed information.

O uso da repetição na escrita pelos surdos

A escrita é uma importante forma de comunicação dos surdos tanto com seus pares quanto com os ouvintes, dada a sua dificuldade em desenvolver a oralidade. Por estarem as marcas de oralidade diretamente relacionadas à coesão textual, este estudo objetivou investigar o uso de repetições na escrita de surdos. Quinze surdos orali%ados, quinze surdos não-oralizados e quinze ouvintes responderam a um questionário analisado quantitativa e qualitativamente em função da ocorrência, tipologia, forma, posição e função das repetições. Os três grupos utilizaram a repetição na escrita. Os dois grupos de surdos apresentaram, majoritariamente, baixa frequência na repetição, integral e adjacente, na escrita. Os oralizados realizaram mais repetições com função de compreensão, enquanto que os não-oralizados realizaram-nas, especialmente, com função de continuidade tópica. Conclui-se que, tal como acontece com os ouvintes, a relação oralidade/escrita ocorre nos surdos, mesmo que eles não tenham tido acesso natural à oralidade da língua. E esta relação ocorre independentemente de eles serem oralizados ou não.

Assistive educational technology

Despite the importance of literacy to employment and social well-being, the literacy rate of the visually impaired and deaf population is estimated to be quite low. Braille, the primary method of reading and writing for the blind, is a tactile system in which embossed dots representing letters and numbers can be read with the fingers. Similarly, the primary method of communication for the deaf is sign language. Sign language simultaneously combines hand shapes, orientation and movement of the hands, arms or body, and facial expressions to express fluidly a deaf speaker's thoughts. As is the case in spoken language, Braille and sign language can differ from one region to another, but the basic elements of both Braille and sign language remain consistent across cultures. A significant problem in education for both the deaf and visually impaired populations is that they are minority populations and hence often have less guided practice in communication. They also participate in fewer interactions with the larger community that reinforce their literacy and communication skills. Finally, the focus of technological enhancements to education has primarily focused on the majority populations, and hence very few automated tutors and educational computing games have been created for visually impaired and deaf children. Our work aims to remedy this situation by developing assistive technology to enhance education for the visually impaired and deaf populations throughout the world. We have developed several tools including a Braille writing tutor (BWT) and the DeSIGN software application, which provides guided practice for communication using sign language. The BWT is a device that connects to a computer through a USB cable. As the student writes each Braille letter or number, the tutor provides immediate audio feedback by repeating the written characters and guiding writing through audio cues, and a variety of curricular and game modes. The DeSIGN tool aims to increase the reading level of the students who are taught to communicate using sign language by reinforcing the mapping between vocabulary and signs through lessons, tests, and games. It also has an interactive game, which provides teachers with a customizable tool for motivating students.

Speech motor learning in profoundly deaf adults.

Speech production, like other sensorimotor behaviors, relies on multiple sensory inputs — audition, proprioceptive inputs from muscle spindles, and cutaneous inputs from mechanoreceptors in the skin and soft tissues of the vocal tract. However, the capacity for intelligible speech by deaf speakers suggests that somatosensory input on its own may contribute to speech motor control and perhaps even to speech learning. We assessed speech motor learning in cochlear implant recipients who were tested with their implants turned off. A robotic device was used to alter somatosensory feedback by displacing the jaw during speech. We found that with training implant subjects progressively adapted to the mechanical perturbation. Moreover, the corrections we observed were for movement deviations that were exceedingly small, on the order of millimetres, indicating that speakers have precise somatosensory expectations. Speech motor learning is significantly dependent on somatosensory input.

Effect of Cochlear Implantation on Nasality in Children

Hypernasality is a commonly perceived characteristic of speech in deaf adults and children, but the mechanism of this abnormal nasal resonance is poorly understood. The impact of cochlear implantation on nasalance measures in children with severe auditory deprivation has not been previously reported. We conducted a study of nasality in 6 deaf children who had undergone cochlear implantation. Voice recordings were obtained before surgery and 6 months after activation of the implants. The MacKay-Kummer SNAP Test--which consists of a syllable-repetition subtest and a picture-cued subtest--was used to obtain nasalance scores for oral (bilabial, alveolar, velar, and sibilant) and nasal phonemes. Before cochlear implantation, mean nasalance scores were significantly higher than normal during the production of oral phonemes for both subtests (p < or = 0.05). Six months after activation, the nasalance measures for all components of the syllable-repetition subtest had been restored to within 1 standard deviation of normal. For all oral phonemes of the picture-cued subtest, the elevated nasalance scores were consistently lower after cochlear implant activation, although the difference was statistically significant only for velar tasks. Nasalance scores for nasal phonemes were within 1 standard deviation of normal both before and after implant activation. Our study showed that cochlear implantation partially corrects elevated nasalance measures. Disturbances in nasal resonance may be caused in part by the inability of deaf speakers to monitor velopharyngeal valving with auditory feedback. The trend toward improved nasalance scores after implantation highlights the role of auditory feedback in monitoring velopharyngeal function. Visual biofeedback may be required to further normalize hypernasal speech in profoundly deaf children.

Speech motor learning without hearing

The nervous system receives both auditory and somatosensory information as we talk. Little is known about the role of somatosensory input in speech motor control. It is indeed a longstanding puzzle how post-lingually deaf speakers, in the absence of any substantial auditory input, maintain speech intelligibility. In this study we have assessed the role of somatosensory feedback in subjects with cochlear implants who were tested with their implants turned off. We used a robotic device to alter speech movements, and hence somatosensory feedback, by delivering mechanical loads to the jaw. We found that with training subjects corrected for the loads, such that the motion path approached that normally experienced under no-load conditions. Thus even under no auditory feedback, somatosensory input mediates speech movements in post-lingually deaf adults. In this study all five subjects with cochlear implants showed varying degrees of adaptation compared to only four out of six subjects in an age matched control group. This suggests a prominent role for somatosensory feedback in individuals with hearing loss. Finally, movement kinematic patterns for subjects with hearing loss were no different than those of subjects with normal hearing, which further underscores the reliance on somatosensory feedback in deaf adults.

Control of Voice-Onset Time in the Absence of Hearing

The relation between partial or absent hearing and control of the voicing contrast has long been of interest to investigators, in part because speakers who are born deaf characteristically have great difficulty mastering the contrast and in part for the light it can cast on the role of hearing in the acquisition and maintenance of phonological contrasts in general. One of the phonetic characteristics that distinguish voiced from voiceless plosives in English (p/b, t/d, k/g) is voice onset time (VOT): the interval from plosive release to the onset of voicing of the following vowel. This article first reviews research on VOT anomalies in the speech production of prelingually and postlingually deaf speakers. Then it turns to studies of the mechanisms in speech breathing, phonation and articulation that underlie those anomalies. In both populations of speakers, there is a tendency for the difference between voiced and voiceless VOT to be reduced, to the point for many speakers that there is in effect a substitution of the voiced for the voiceless cognate. The separation of the cognate VOTs can be enhanced when some hearing is restored with a cochlear implant. Both populations also present anomalies in speech breathing that can hinder the development of intraoral pressures and transglottal pressure drops that are required for the production of the VOT contrast. Its successful management further requires critical timing among phonatory and articulatory gestures, most of which are not visible, rendering the VOT contrast a particular challenge in the absence of hearing.

Effects of bite blocks and hearing status on vowel production

This study explores the effects of hearing status and bite blocks on vowel production. Normal-hearing controls and postlingually deaf adults read elicitation lists of /hVd/ syllables with and without bite blocks and auditory feedback. Deaf participants' auditory feedback was provided by a cochlear prosthesis and interrupted by switching off their implant microphones. Recording sessions were held before prosthesis was provided and one month and one year after. Long-term absence of auditory feedback was associated with heightened dispersion of vowel tokens, which was inflated further by inserting bite blocks. The restoration of some hearing with prosthesis reduced dispersion. Deaf speakers' vowel spaces were reduced in size compared to controls. Insertion of bite blocks reduced them further because of the speakers' incomplete compensation. A year of prosthesis use increased vowel contrast with feedback during elicitation. These findings support the inference that models of speech production must assign a role to auditory feedback in error-based correction of feedforward commands for subsequent articulatory gestures.

Perception and production of /r/ allophones improve with hearing from a cochlear implant

While variations in tongue shape for /r/ occur in different contexts, they normally result in only small changes in the primary acoustic cue (lowered F3). It was hypothesized that deaf speakers would show larger allophonic variation than normal-hearing speakers and that auditory feedback from a cochlear implant would reduce that variability. In this study, acoustic variation of stop and stop+/r/ tokens was evaluated pre- and post-implant (n=8) and once in normal-hearing controls (n=8). Measures included (1) r-variation: distance from the center of the distribution defined by the F3 transition and the value of F3 minus F2 at the /r/-vowel boundary for wabrav, wadrav, and wagrav tokens (2) vowel variation: distance from the center of F1, F2 for the second /a/ in wabav, wadav, and wagav tokens and (3) pairwise r-variation normalized by vowel variation. Pre-implant, seven of eight speakers had significantly greater normalized /r/ variation than the hearing speakers mean. Post-implant, seven of eight speakers had normalized /r/ are variation that was not different from the control mean. Implant users perception and production of stop and stop+/r/ blend productions improved; however, their /b-br/ and /g-gr/ contrast distances were still smaller one-year post-implant than the controls. [Research supported by NIDCD.]

VOT and hearing impairment

When deafened adults recover some hearing after receiving a cochlear implant, numerous changes in their speech occur at both phonemic and suprasegmental levels. If a change toward normative values is observed for some phonemic parameter, it may be attributed to the restored hearing; however, it may be a by-product of a suprasegmental change. Consistent with results reported for speakers with normal hearing, Lane et al. [J. Acoust. Soc. Am. 98, 3096–3106 (1995)] observed in implant users that VOT varies approximately linearly with syllable duration. Therefore, in comparing pre- and postimplant measures of VOT in five speakers, each token’s VOT was adjusted for the change in syllable duration of that token relative to the mean syllable duration in a baseline session (called VOTc). Preimplant, the deaf speakers characteristically uttered plosives with abnormally short VOTc. With some hearing restored, four of the five lengthened VOTc. Changes in voiced plosives’ VOTc with restored hearing were correlated with changes in SPL. Some of the reliable VOTc increases that were not correlated with SPL may have been caused by auditory validation of an internal model for phoneme production. Recent studies of VOT in hearing-impaired speakers will be reviewed in this light. [Work supported by NIDCD, NIH.]

Somatosensory basis of speech production.

The hypothesis that speech goals are defined acoustically and maintained by auditory feedback is a central idea in speech production research. An alternative proposal is that speech production is organized in terms of control signals that subserve movements and associated vocal-tract configurations. Indeed, the capacity for intelligible speech by deaf speakers suggests that somatosensory inputs related to movement play a role in speech production-but studies that might have documented a somatosensory component have been equivocal. For example, mechanical perturbations that have altered somatosensory feedback have simultaneously altered acoustics. Hence, any adaptation observed under these conditions may have been a consequence of acoustic change. Here we show that somatosensory information on its own is fundamental to the achievement of speech movements. This demonstration involves a dissociation of somatosensory and auditory feedback during speech production. Over time, subjects correct for the effects of a complex mechanical load that alters jaw movements (and hence somatosensory feedback), but which has no measurable or perceptible effect on acoustic output. The findings indicate that the positions of speech articulators and associated somatosensory inputs constitute a goal of speech movements that is wholly separate from the sounds produced.

Speech Science: An Integrated Approach to Theory and Clinical Practice

Speech Science: An Integrated Approach to Theory and Clinical Practice

The effects of changes in hearing status in cochlear implant users on the acoustic vowel space and CV coarticulation.

In order to examine the role of hearing status in controlling coarticulation, eight English vowels in /bVt/ and /dVt/ syllables, embedded in a carrier phrase, were elicited from 7 postlingually deafened adults and 2 speakers with normal hearing. The deaf adults served in repeated recording sessions both before and up to a year after they received cochlear implants and their speech processors were turned on. Each of the two hearing control speakers served in two recording sessions, separated by about 3 months. Measures were made of second formant frequency at obstruent release and at 25 ms intervals until the final obstruent. An index of coarticulation, based on the ratio of F2 at vowel onset to F2 at midvowel target, was computed. Changes in the amount of coarticulation after the change in hearing status were small and nonsystematic for the /bVt/ syllables; those for the /dVt/ syllables averaged a 3% increase--within the range of reliability measures for the 2 hearing control speakers. Locus equations (F2 at vowel onset vs. F2 at vowel midpoint) and ratios of F2 onsets in point vowels were also calculated. Like the index of coarticulation, these measures tended to confirm that hearing status had little if any effect on coarticulation in the deaf speakers, consistent with the hypothesis that hearing does not play a direct role in regulating anticipatory coarticulation in adulthood. With the restoration of some hearing, 2 implant users significantly increased the average spacing between vowels in the formant plane, whereas the remaining 5 decreased that measure. All speakers but one also reduced vowel duration significantly. Four of the speakers reduced dispersion of vowel formant values around vowel midpoint means, but the other 3 did not show this effect.

The effect of changes in hearing status on speech sound level and speech breathing: a study conducted with cochlear implant users and NF-2 patients.

According to a dual-process theory of the role of hearing in speech production, hearing helps maintain an internal model used by the speech control mechanism to achieve phonemic goals. It also monitors the acoustic environment and guides relatively rapid adjustments in postural parameters, such as those underlying average speech sound level and rate, in order to achieve suprasegmental goals that are a compromise between intelligibility and economy of effort. In order to obtain evidence bearing on this theory, acoustic and aerodynamic measures were collected from seven adventitiously deaf speakers who received cochlear implants, three speakers who had severe reduction in hearing following surgery for Neurofibromatosis-2, and one hard of hearing speaker. These speakers made recordings of the Rainbow Passage and an English vowel inventory before and after intervention. All but one of the postlingually deaf speakers who received prosthetic hearing reduced speech sound level, SPL. Three of these significantly increased a measure of inferred glottal aperture, H1-H2, and their session means for these two parameters were inversely correlated longitudinally. All but one of the speakers terminated respiratory limbs closer to functional residual capacity (FRC) once prosthetic hearing was supplied. Finally, the implant users' average values of air expenditure moved toward normative values with prosthetic hearing. These results are attributed to the mediation of changes in respiratory and glottal posture aimed at reducing speech sound level and economizing effort.