Speech of cochlear implant patients: a longitudinal study of vowel production

The Accompanying Effect in Responses to Auditory Perturbations: Unconscious Vocal Adjustments to Unperturbed Parameters

PURPOSE

The present study examined whether participants respond to unperturbed parameters while experiencing specific perturbations in auditory feedback. For instance, we aim to determine if speakers adjust voice loudness when only pitch is artificially altered in auditory feedback. This phenomenon is referred to as the "accompanying effect" in the present study.

METHOD

Thirty native Mandarin speakers were asked to sustain the vowel /ɛ/ for 3 s while their auditory feedback underwent single shifts in one of the three distinct ways: pitch shift (±100 cents; coded as PT), loudness shift (±6 dB; coded as LD), or first formant (F1) shift (±100 Hz; coded as FM). Participants were instructed to ignore the perturbations in their auditory feedback. Response types were categorized based on pitch, loudness, and F1 for each individual trial, such as Popp_Lopp_Fopp indicating opposing responses in all three domains.

RESULTS

The accompanying effect appeared 93% of the time. Bayesian Poisson regression models indicate that opposing responses in all three domains (Popp_Lopp_Fopp) were the most prevalent response type across the conditions (PT, LD, and FM). The more frequently used response types exhibited opposing responses and significantly larger response curves than the less frequently used response types. Following responses became more prevalent only when the perturbed stimuli were perceived as voices from someone else (external references), particularly in the FM condition. In terms of isotropy, loudness and F1 tended to change in the same direction rather than loudness and pitch.

CONCLUSION

The presence of the accompanying effect suggests that the motor systems responsible for regulating pitch, loudness, and formants are not entirely independent but rather interconnected to some degree.

A neurocomputational view of the effects of Parkinson's disease on speech production

The purpose of this article is to review the scientific literature concerning speech in Parkinson's disease (PD) with reference to the DIVA/GODIVA neurocomputational modeling framework. Within this theoretical view, the basal ganglia (BG) contribute to several different aspects of speech motor learning and execution. First, the BG are posited to play a role in the initiation and scaling of speech movements. Within the DIVA/GODIVA framework, initiation and scaling are carried out by initiation map nodes in the supplementary motor area acting in concert with the BG. Reduced support of the initiation map from the BG in PD would result in reduced movement intensity as well as susceptibility to early termination of movement. A second proposed role concerns the learning of common speech sequences, such as phoneme sequences comprising words; this view receives support from the animal literature as well as studies identifying speech sequence learning deficits in PD. Third, the BG may play a role in the temporary buffering and sequencing of longer speech utterances such as phrases during conversational speech. Although the literature does not support a critical role for the BG in representing sequence order (since incorrectly ordered speech is not characteristic of PD), the BG are posited to contribute to the scaling of individual movements in the sequence, including increasing movement intensity for emphatic stress on key words. Therapeutic interventions for PD have inconsistent effects on speech. In contrast to dopaminergic treatments, which typically either leave speech unchanged or lead to minor improvements, deep brain stimulation (DBS) can degrade speech in some cases and improve it in others. However, cases of degradation may be due to unintended stimulation of efferent motor projections to the speech articulators. Findings of spared speech after bilateral pallidotomy appear to indicate that any role played by the BG in adult speech must be supplementary rather than mandatory, with the sequential order of well-learned sequences apparently represented elsewhere (e.g., in cortico-cortical projections).

On the interplay between speech perception and production: insights from research and theories

The study of spoken communication has long been entrenched in a debate surrounding the interdependence of speech production and perception. This mini review summarizes findings from prior studies to elucidate the reciprocal relationships between speech production and perception. We also discuss key theoretical perspectives relevant to speech perception-production loop, including hyper-articulation and hypo-articulation (H&H) theory, speech motor theory, direct realism theory, articulatory phonology, the Directions into Velocities of Articulators (DIVA) and Gradient Order DIVA (GODIVA) models, and predictive coding. Building on prior findings, we propose a revised auditory-motor integration model of speech and provide insights for future research in speech perception and production, focusing on the effects of impaired peripheral auditory systems.

Role of Voice Handicap Index in Evaluation of Patients with Moderate to Severe Bilateral Sensorineural Hearing Loss

Background

Our ability to hear and speak enables us to communicate with others, forming an integral part of our emotional and social well-being. Vocal problems in hearing-impaired patients have yet to be assessed in terms of subjective level of disability they cause. Present study aims to assess the different Voice Handicap Index (VHI) scores among patients with moderate to severe sensorineural hearing loss and compare them to those with normal hearing.

Materials and Methods

In this prospective case control study(n = 150), study group A (n = 100) consisted of subjects with bilateral moderate to profound hearing loss on Pure tone audiometry and control group B (n = 50) with normal hearing. Both groups were asked to fill out VHI form after a normal videostroboscopic assessment.

Results

Mean VHI score in group A was 57.5 ± 12.48 and 6.0 ± 3.24 in group B, difference being statistically significant. A strong positive correlation was found between severity of hearing loss and VHI total score. The difference between both groups was also statistically significant for each of the three subscales of VHI.

Conclusion

We infer that subjects with moderate and higher bilateral sensorineural hearing loss hearing have statistically significant higher VHI scores as compared to those with normal hearing. It was observed that perception of voice handicap increased with the severity of hearing loss. These findings emphasize the need for multilateral assessment and treatment of voice disorders in subjects with hearing loss.

The Impact of Bimodal Hearing on Speech Acoustics of Vowel Production in Adult Cochlear Implant Users

PURPOSE

This study aimed to investigate the acoustic changes in vowel production with different forms of auditory feedback via cochlear implant (CI), hearing aid (HA), and bimodal hearing (CI + HA).

METHOD

Ten post-lingually deaf adult bimodal CI users (aged 50-78 years) produced English vowels /i/, /ɛ/, /æ/, /ɑ/, /ʊ/, and /u/ in the context of /hVd/ during short-term use of no device (ND), HA, CI, and CI + HA. Segmental features (first formant frequency [F 1], second formant frequency [F 2], and vowel space area) and suprasegmental features (duration, intensity, and fundamental frequency [f o]) of vowel production were analyzed. Participants also categorized a vowel continuum synthesized from their own productions of /ɛ/ and /æ/ using HA, CI, and CI + HA.

RESULTS

F 1s of all vowels decreased; F 2s of front vowels but not back vowels increased; vowel space areas increased; and vowel durations, intensities, and f os decreased with statistical significance in the HA, CI, and CI + HA conditions relative to the ND condition. Only f os were lower, and vowel space areas were larger with CI and CI + HA than with HA. Average changes in f o, intensity, and F 1 from the ND condition to the HA, CI, and CI + HA conditions were positively correlated. Most participants did not show a typical psychometric function for vowel categorization, and thus, the relationship between vowel categorization and production was not tested.

CONCLUSIONS

The results suggest that acoustic, electric, and bimodal hearing have a measurable impact on vowel acoustics of post-lingually deaf adults when their hearing devices are turned on and off temporarily. Also, changes in f o and F 1 with the use of hearing devices may be largely driven by changes in intensity.

Effects of Gradual and Sudden Introduction of Perturbations on Adaptive Responses to Formant-Shift and Formant-Clamp Perturbations

PURPOSE

When the speech motor system encounters errors, it generates adaptive responses to compensate for the errors. Unlike errors induced by formant-shift perturbations, errors induced by formant-clamp perturbations do not correspond with the speaker's speech (i.e., degraded motor-to-auditory correspondence). We previously showed that adaptive responses to formant-clamp perturbations are smaller than responses to formant-shift perturbations when perturbations are introduced gradually. This study examined responses to formant-clamp and formant-shift perturbations when perturbations are introduced suddenly.

METHOD

One group of participants (n = 30) experienced gradually introduced formant-clamp and formant-shift perturbations, and another group (n = 30) experienced suddenly introduced formant-clamp and formant-shift perturbations. We designed the perturbations based on participant-specific vowel configurations such that a participant's first and second formants of /ɛ/ were perturbed toward their /æ/. To estimate adaptive responses, we measured formant changes (0-100 ms of the vowel) in response to the formant perturbations.

RESULTS

We found that (a) the difference between responses to formant-clamp and formant-shift perturbations was smaller when the perturbations were introduced suddenly and (b) responses to suddenly introduced (but not gradually introduced) formant-shift perturbations positively correlated with responses to formant-clamp perturbations.

CONCLUSIONS

These results showed that the speech motor system responds to errors induced by formant-shift and formant-clamp perturbations more differently when perturbations are introduced gradually than suddenly. Overall, the quality of errors (formant-shift vs. formant-clamp) and the manner of introducing errors (gradually vs. suddenly) modulate the speech motor system's evaluations of and responses to errors.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.22406422.

Adult Cochlear Implant Users Versus Typical Hearing Persons: An Automatic Analysis of Acoustic-Prosodic Parameters

PURPOSE

The aim of this study was to investigate the speech prosody of postlingually deaf cochlear implant (CI) users compared with control speakers without hearing or speech impairment.

METHOD

Speech recordings of 74 CI users (37 males and 37 females) and 72 age-balanced control speakers (36 males and 36 females) are considered. All participants are German native speakers and read Der Nordwind und die Sonne (The North Wind and the Sun), a standard text in pathological speech analysis and phonetic transcriptions. Automatic acoustic analysis is performed considering pitch, loudness, and duration features, including speech rate and rhythm.

RESULTS

In general, duration and rhythm features differ between CI users and control speakers. CI users read slower and have a lower voiced segment ratio compared with control speakers. A lower voiced ratio goes along with a prolongation of the voiced segments' duration in male and with a prolongation of pauses in female CI users. Rhythm features in CI users have higher variability in the duration of vowels and consonants than in control speakers. The use of bilateral CIs showed no advantages concerning speech prosody features in comparison to unilateral use of CI.

CONCLUSIONS

Even after cochlear implantation and rehabilitation, the speech of postlingually deaf adults deviates from the speech of control speakers, which might be due to changed auditory feedback. We suggest considering changes in temporal aspects of speech in future rehabilitation strategies.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.21579171.

Assessing Ecologically Valid Methods of Auditory Feedback Measurement in Individuals With Typical Speech

PURPOSE

Auditory feedback is thought to contribute to the online control of speech production. Yet, the standard method of estimating auditory feedback control (i.e., reflexive responses to auditory-motor perturbations), although sound, requires specialized instrumentation, meticulous calibration, unnatural tasks, and specific acoustic environments. The purpose of this study was to explore more ecologically valid features of speech production to determine their relationships with auditory feedback mechanisms.

METHOD

Two previously proposed measures of within-utterance variability (centering and baseline variability) were compared with reflexive response magnitudes in 30 adults with typical speech. These three measures were estimated for both the laryngeal and articulatory subsystems of speech.

RESULTS

Regardless of the speech subsystem, neither centering nor baseline variability was shown to be related to reflexive response magnitudes. Likewise, no relationships were found between centering and baseline variability.

CONCLUSIONS

Despite previous suggestions that centering and baseline variability may be related to auditory feedback mechanisms, this study did not support these assertions. However, the detection of such relationships may have required a larger degree of variability in responses, relative to that found in those with typical speech. Future research on these relationships is warranted in populations with more heterogeneous responses, such as children or clinical populations.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.17330546.

Real-time feedback control of voice in cochlear implant recipients

OBJECTIVES

To evaluate feedback-dependent vocal control in cochlear implant patients using pitch-shifted auditory feedback.

METHODS

Twenty-three CI recipients with at least 6 months of implant experience were enrolled. Vocal recordings were performed while subjects repeated the vowel /e/ and vocal signals were altered in real-time using a digital effects processor to introduce a pitch-shift, presented back to subjects using headphones. Recordings were analyzed to determine pitch changes following the pitch-shifted feedback, and results compared to the magnitude of the shift as well as patient demographics.

RESULTS

Consistent with previous results, CI patients' voices had higher pitches with their implant turned off, a change explainable by increases in vocal loudness without the CI. CI patients rapidly compensated for pitch-shifted feedback by changing their vocal pitch, but only for larger shifts. Considerable inter-subject variability was present, and weakly correlated with the duration of implant experience and implant sound thresholds.

CONCLUSIONS

CI patients, like normal hearing individuals, are capable of real-time feedback-dependent control of their vocal pitch. However, CI patients are less sensitive to small feedback changes, possibly a result of courser CI frequency precision, and may explain poorer than normal vocal control in these patients.

LEVEL OF EVIDENCE

Level 3b.

Contributions of Auditory and Somatosensory Feedback to Vocal Motor Control

Purpose To better define the contributions of somatosensory and auditory feedback in vocal motor control, a laryngeal perturbation experiment was conducted with and without masking of auditory feedback. Method Eighteen native speakers of English produced a sustained vowel while their larynx was physically and externally displaced on a subset of trials. For the condition with auditory masking, speech-shaped noise was played via earphones at 90 dB SPL. Responses to the laryngeal perturbation were compared to responses by the same participants to an auditory perturbation experiment that involved a 100-cent downward shift in fundamental frequency (f _o). Responses were also examined in relation to a measure of auditory acuity. Results Compensatory responses to the laryngeal perturbation were observed with and without auditory masking. The level of compensation was greatest in the laryngeal perturbation condition without auditory masking, followed by the condition with auditory masking; the level of compensation was smallest in the auditory perturbation experiment. No relationship was found between the degree of compensation to auditory versus laryngeal perturbations, and the variation in responses in both perturbation experiments was not related to auditory acuity. Conclusions The findings indicate that somatosensory and auditory feedback control mechanisms work together to compensate for laryngeal perturbations, resulting in the greatest degree of compensation when both sources of feedback are available. In contrast, these two control mechanisms work in competition in response to auditory perturbations, resulting in an overall smaller degree of compensation. Supplemental Material https://doi.org/10.23641/asha.12559628.

Unconscious and Distinctive Control of Vocal Pitch and Timbre During Altered Auditory Feedback

Vocal control plays a critical role in smooth social communication. Speakers constantly monitor auditory feedback (AF) and make adjustments when their voices deviate from their intentions. Previous studies have shown that when certain acoustic features of the AF are artificially altered, speakers compensate for this alteration in the opposite direction. However, little is known about how the vocal control system implements compensations for alterations of different acoustic features, and associates them with subjective consciousness. The present study investigated whether compensations for the fundamental frequency (F0), which corresponds to perceived pitch, and formants, which contribute to perceived timbre, can be performed unconsciously and independently. Forty native Japanese speakers received two types of altered AF during vowel production that involved shifts of either only the formant frequencies (formant modification; Fm) or both the pitch and formant frequencies (pitch + formant modification; PFm). For each type, three levels of shift (slight, medium, and severe) in both directions (increase or decrease) were used. After the experiment, participants were tested for whether they had perceived a change in the F0 and/or formants. The results showed that (i) only formants were compensated for in the Fm condition, while both the F0 and formants were compensated for in the PFm condition; (ii) the F0 compensation exhibited greater precision than the formant compensation in PFm; and (iii) compensation occurred even when participants misperceived or could not explicitly perceive the alteration in AF. These findings indicate that non-experts can compensate for both formant and F0 modifications in the AF during vocal production, even when the modifications are not explicitly or correctly perceived, which provides further evidence for a dissociation between conscious perception and action in vocal control. We propose that such unconscious control of voice production may enhance rapid adaptation to changing speech environments and facilitate mutual communication.

Systematic Review of Auditory Perceptual and Acoustic Characteristics of the Voice of Cochlear Implant Adult Users

STATEMENT OF PROBLEM

What are the normative data available on the perceptual and acoustic characteristics of the voice of adults of both sexes who have hearing-impairment and who use cochlear implants?

PURPOSE

To identify in the literature, normative data about the perceptual auditory and acoustic characteristics of the voice of hearing-impaired cochlear implant adult users.

SEARCH STRATEGY

A systematic search was carried out in the Virtual Health Library, Web of Science, Science Direct, SciELO, and SCOPUS databases with no temporal restriction.

SELECTION CRITERIA

The articles were selected if they led with citation to normative data of the acoustic analysis of the voice of deaf cochlear implant users. And duplicate articles, case studies, letters to the editor, reviews, and studies that were not directly related to the topic were excluded.

DATA EXTRACTION

The data from each article were extracted according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis checklist: title, abstract, year of publication, journal, authors and country of origin, identification of background, purpose, study design, participants, variables, and data measurement.

DATA SYNTHESIS

There were 1,052 publications that met the search criteria. After applying the Preferred Reporting Items for Systematic Reviews and Meta-analysis checklist, excluding duplicates, and reading of the full text, 10 papers were selected for further analysis. Although several voice parameters have been studied, there is a great variation in study designs, sample sizes, age of participants, voice samples analyzed, and cochlear implant specifications.

CONCLUSION

The normative data available in the literature concerning the voice of cochlear implant users are consistent only in terms of fundamental frequency.

Relationships between vocal pitch perception and production: a developmental perspective

The purpose of this study was to examine the relationships between vocal pitch discrimination abilities and vocal responses to auditory pitch-shifts. Twenty children (6.6-11.7 years) and twenty adults (18-28 years) completed a listening task to determine auditory discrimination abilities to vocal fundamental frequency (fo) as well as two vocalization tasks in which their perceived fo was modulated in real-time. These pitch-shifts were either unexpected, providing information on auditory feedback control, or sustained, providing information on sensorimotor adaptation. Children were subdivided into two groups based on their auditory pitch discrimination abilities; children within two standard deviations of the adult group were classified as having adult-like discrimination abilities (N = 11), whereas children outside of this range were classified as having less sensitive discrimination abilities than adults (N = 9). Children with less sensitive auditory pitch discrimination abilities had significantly larger vocal response magnitudes to unexpected pitch-shifts and significantly smaller vocal response magnitudes to sustained pitch-shifts. Children with less sensitive auditory pitch discrimination abilities may rely more on auditory feedback and thus may be less adept at updating their stored motor programs.

Mechanisms of voice control related to prosody in autism spectrum disorder and first-degree relatives

Differences in prosody (e.g., intonation, rhythm) are among the most obvious language-related impairments in autism spectrum disorder (ASD), and significantly impact communication. Subtle prosodic differences have also been identified in a subset of clinically unaffected first-degree relatives of individuals with ASD, and may reflect genetic liability to ASD. This study investigated the neural basis of prosodic differences in ASD and first-degree relatives through analysis of feedforward and feedback control involved in the planning, production, self-monitoring, and self-correction of speech by using a pitch-perturbed auditory feedback paradigm during sustained vowel and speech production. Results revealed larger vocal response magnitudes to pitch-perturbed auditory feedback across tasks in ASD and ASD parent groups, with differences in sustained vowel production driven by parents who displayed subclinical personality and language features associated with ASD (i.e., broad autism phenotype). Both ASD and ASD parent groups exhibited increased response onset latencies during sustained vowel production, while the ASD parent group exhibited decreased response onset latencies during speech production. Vocal response magnitudes across tasks were associated with prosodic atypicalities in both individuals with ASD and their parents. Exploratory event-related potential (ERP) analyses in a subgroup of participants during the sustained vowel task revealed reduced P1 ERP amplitudes in the ASD group, with similar trends observed in parents. Overall, results suggest underdeveloped feedforward systems and neural attenuation in detecting audio-vocal feedback may contribute to ASD-related prosodic atypicalities. Importantly, results implicate atypical audio-vocal integration as a marker of genetic risk to ASD, evident in ASD and among clinically unaffected relatives. Autism Res 2019, 12: 1192-1210. © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: Previous research has identified atypicalities in prosody (e.g., intonation) in individuals with ASD and a subset of their first-degree relatives. In order to better understand the mechanisms underlying prosodic differences in ASD, this study examined how individuals with ASD and their parents responded to unexpected differences in what they heard themselves say to modify control of their voice (i.e., audio-vocal integration). Results suggest that disruptions to audio-vocal integration in individuals with ASD contribute to ASD-related prosodic atypicalities, and the more subtle differences observed in parents could reflect underlying genetic liability to ASD.

Basic Measures of Prosody in Spontaneous Speech of Children With Early and Late Cochlear Implantation

PURPOSE

Relative to normally hearing (NH) peers, the speech of children with cochlear implants (CIs) has been found to have deviations such as a high fundamental frequency, elevated jitter and shimmer, and inadequate intonation. However, two important dimensions of prosody (temporal and spectral) have not been systematically investigated. Given that, in general, the resolution in CI hearing is best for the temporal dimension and worst for the spectral dimension, we expected this hierarchy to be reflected in the amount of CI speech's deviation from NH speech. Deviations, however, were expected to diminish with increasing device experience.

METHOD

Of 9 Dutch early- and late-implanted (division at 2 years of age) children and 12 hearing age-matched NH controls, spontaneous speech was recorded at 18, 24, and 30 months after implantation (CI) or birth (NH). Six spectral and temporal outcome measures were compared between groups, sessions, and genders.

RESULTS

On most measures, interactions of Group and/or Gender with Session were significant. For CI recipients as compared with controls, performance on temporal measures was not in general more deviant than spectral measures, although differences were found for individual measures. The late-implanted group had a tendency to be closer to the NH group than the early-implanted group. Groups converged over time.

CONCLUSIONS

Results did not support the phonetic dimension hierarchy hypothesis, suggesting that the appropriateness of the production of basic prosodic measures does not depend on auditory resolution. Rather, it seems to depend on the amount of control necessary for speech production.

Vocal Biomarkers of Mild-to-Moderate Hearing Loss in Children and Adults: Voiceless Sibilants

PURPOSE

The purpose of this study was to determine if an objective measure of speech production could serve as a vocal biomarker for the effects of high-frequency hearing loss on speech perception. It was hypothesized that production of voiceless sibilants is governed sufficiently by auditory feedback that high-frequency hearing loss results in subtle but significant shifts in the spectral characteristics of these sibilants.

METHOD

Sibilant production was examined in individuals with mild to moderately severe congenital (22 children; 8-17 years old) and acquired (23 adults; 55-80 years old) hearing losses. Measures of hearing level (pure-tone average thresholds at 4 and 8 kHz), speech perception (detection of nonsense words within sentences), and speech production (spectral center of gravity [COG] for /s/ and /ʃ/) were obtained in unaided and aided conditions.

RESULTS

For both children and adults, detection of nonsense words increased significantly as hearing thresholds improved. Spectral COG for /ʃ/ was unaffected by hearing loss in both listening conditions, whereas the spectral COG for /s/ significantly decreased as high-frequency hearing loss increased. The distance in spectral COG between /s/ and /ʃ/ decreased significantly with increasing hearing level. COG distance significantly predicted nonsense-word detection in children but not in adults.

CONCLUSIONS

At least one aspect of speech production (voiceless sibilants) is measurably affected by high-frequency hearing loss and is related to speech perception in children. Speech production did not predict speech perception in adults, suggesting a more complex relationship between auditory feedback and feedforward mechanisms with age. Even so, these results suggest that this vocal biomarker may be useful for identifying the presence of high-frequency hearing loss in adults and children and for predicting the impact of hearing loss in children.

Gated Word Recognition by Postlingually Deafened Adults With Cochlear Implants: Influence of Semantic Context

PURPOSE

The main goal of this study was to investigate the minimum amount of sensory information required to recognize spoken words (isolation points [IPs]) in listeners with cochlear implants (CIs) and investigate facilitative effects of semantic contexts on the IPs.

METHOD

Listeners with CIs as well as those with normal hearing (NH) participated in the study. In Experiment 1, the CI users listened to unprocessed (full-spectrum) stimuli and individuals with NH listened to full-spectrum or vocoder processed speech. IPs were determined for both groups who listened to gated consonant-nucleus-consonant words that were selected based on lexical properties. In Experiment 2, the role of semantic context on IPs was evaluated. Target stimuli were chosen from the Revised Speech Perception in Noise corpus based on the lexical properties of the final words.

RESULTS

The results indicated that spectrotemporal degradations impacted IPs for gated words adversely, and CI users as well as participants with NH listening to vocoded speech had longer IPs than participants with NH who listened to full-spectrum speech. In addition, there was a clear disadvantage due to lack of semantic context in all groups regardless of the spectral composition of the target speech (full spectrum or vocoded). Finally, we showed that CI users (and users with NH with vocoded speech) can overcome such word processing difficulties with the help of semantic context and perform as well as listeners with NH.

CONCLUSION

Word recognition occurs even before the entire word is heard because listeners with NH associate an acoustic input with its mental representation to understand speech. The results of this study provide insight into the role of spectral degradation on the processing of spoken words in isolation and the potential benefits of semantic context. These results may also explain why CI users rely substantially on semantic context.

Speech Production Quality of Cochlear Implant Users with Respect to Duration and Onset of Hearing Loss

PURPOSE

To assess whether postlingual onset and shorter duration of deafness before cochlear implant (CI) provision predict higher speech intelligibility results of CI users.

METHODS

For an objective judgement of speech intelligibility, we used an automatic speech recognition system computing the word recognition rate (WR) of 50 adult CI users and 50 age-matched control individuals. All subjects were recorded reading a standardized text. Subjects were divided into three groups: pre- or perilingual deafness (A), both >2 years before implantation, postlingual deafness <2 years before implantation (B), or postlingual deafness >2 years before implantation (C).

RESULTS

CI users with short duration of postlingual deafness (B) had a significantly higher WR (median 74%) than CI users with long duration of postlingual deafness (C; 68%, p < 0.001) or pre-/perilingual onset (A; 56%, p < 0.001). Compared to their control groups only CI users with short duration of postlingual deafness reached similar WR, others showed significantly lower WR. Other factors such as hearing loss onset, duration of CI use, or duration of amplified hearing showed no consistent influence on speech quality.

CONCLUSIONS

The speech production quality of adult CI users shows dependencies on the onset and duration of deafness. These features need to be considered while planning rehabilitation.

Sensory-motor relationships in speech production in post-lingually deaf cochlear-implanted adults and normal-hearing seniors: Evidence from phonetic convergence and speech imitation

Speech communication can be viewed as an interactive process involving a functional coupling between sensory and motor systems. One striking example comes from phonetic convergence, when speakers automatically tend to mimic their interlocutor's speech during communicative interaction. The goal of this study was to investigate sensory-motor linkage in speech production in postlingually deaf cochlear implanted participants and normal hearing elderly adults through phonetic convergence and imitation. To this aim, two vowel production tasks, with or without instruction to imitate an acoustic vowel, were proposed to three groups of young adults with normal hearing, elderly adults with normal hearing and post-lingually deaf cochlear-implanted patients. Measure of the deviation of each participant's f₀ from their own mean f₀ was measured to evaluate the ability to converge to each acoustic target.

RESULTS

showed that cochlear-implanted participants have the ability to converge to an acoustic target, both intentionally and unintentionally, albeit with a lower degree than young and elderly participants with normal hearing. By providing evidence for phonetic convergence and speech imitation, these results suggest that, as in young adults, perceptuo-motor relationships are efficient in elderly adults with normal hearing and that cochlear-implanted adults recovered significant perceptuo-motor abilities following cochlear implantation.

Sensorimotor control of vocal pitch and formant frequencies in Parkinson's disease

BACKGROUND

Auditory feedback reflects information on multiple speech parameters including fundamental frequency (pitch) and formant properties. Inducing auditory errors in these acoustic parameters during speech production has been used to examine the manner in which auditory feedback is integrated with ongoing speech motor processes. This integration has been shown to be impaired in disorders such as Parkinson's disease (PD), in which individuals exhibit difficulty adjusting to altered sensory-motor relationships. The current investigation examines whether such sensorimotor impairments affect fundamental frequency and formant parameters of speech differentially.

METHODS

We employed a sensorimotor compensation paradigm to investigate the mechanisms underlying the control of vocal pitch and formant parameters. Individuals with PD and age-matched controls prolonged a speech vowel in the context of a word while the fundamental or first formant frequency of their auditory feedback was altered unexpectedly on random trials, using two magnitudes of perturbation.

RESULTS

Compared with age-matched controls, individuals with PD exhibited a larger compensatory response to fundamental frequency perturbations, in particular in response to the smaller magnitude alteration. In contrast, the group with PD showed reduced compensation to first formant frequency perturbations.

CONCLUSIONS

The results demonstrate that the neural processing impairment of PD differentially affects the processing of auditory feedback for the control of fundamental and formant frequency. The heightened modulation of fundamental frequency in response to auditory perturbations may reflect a change in sensory weighting due to somatosensory deficits associated with the larynx, while the reduced ability to modulate vowel formants may result from impaired activation of the oral articulatory musculature.

Gradual adaptation to auditory frequency mismatch

What is the best way to help humans adapt to a distorted sensory input? Interest in this question is more than academic. The answer may help facilitate auditory learning by people who became deaf after learning language and later received a cochlear implant (a neural prosthesis that restores hearing through direct electrical stimulation of the auditory nerve). There is evidence that some cochlear implants (which provide information that is spectrally degraded to begin with) stimulate neurons with higher characteristic frequency than the acoustic frequency of the original stimulus. In other words, the stimulus is shifted in frequency with respect to what the listener expects to hear. This frequency misalignment may have a negative influence on speech perception by CI users. However, a perfect frequency-place alignment may result in the loss of important low frequency speech information. A trade-off may involve a gradual approach: start with correct frequency-place alignment to allow listeners to adapt to the spectrally degraded signal first, and then gradually increase the frequency shift to allow them to adapt to it over time. We used an acoustic model of a cochlear implant to measure adaptation to a frequency-shifted signal, using either the gradual approach or the "standard" approach (sudden imposition of the frequency shift). Listeners in both groups showed substantial auditory learning, as measured by increases in speech perception scores over the course of fifteen one-hour training sessions. However, the learning process was faster for listeners who were exposed to the gradual approach. These results suggest that gradual rather than sudden exposure may facilitate perceptual learning in the face of a spectrally degraded, frequency-shifted input. This article is part of a Special Issue entitled <Lasker Award>.

Five decades of research in speech motor control: what have we learned, and where should we go from here?

PURPOSE

The author presents a view of research in speech motor control over the past 5 decades, as observed from within Ken Stevens's Speech Communication Group (SCG) in the Research Laboratory of Electronics at MIT.

METHOD

The author presents a limited overview of some important developments and discoveries. The perspective is based largely on the research interests of the Speech Motor Control Group (SMCG) within the SCG; thus, it is selective, focusing on normal motor control of the vocal tract in the production of sound segments and syllables. It also covers the particular theories and models that drove the research. Following a brief introduction, there are sections on methodological advances, scientific advances, and conclusions.

RESULTS

Scientific and methodological advances have been closely interrelated. Advances in instrumentation and computer hardware and software have made it possible to record and process increasingly large, multifaceted data sets; introduce new paradigms for feedback perturbation; image brain activity; and develop more sophisticated, computational physiological and neural models. Such approaches have led to increased understanding of the widespread variability in speech, motor-equivalent trading relations, sensory goals, and the nature of feedback and feedforward neural control mechanisms.

CONCLUSIONS

Some ideas about important future directions for speech research are presented.

The process of spoken word recognition in the face of signal degradation

Though much is known about how words are recognized, little research has focused on how a degraded signal affects the fine-grained temporal aspects of real-time word recognition. The perception of degraded speech was examined in two populations with the goal of describing the time course of word recognition and lexical competition. Thirty-three postlingually deafened cochlear implant (CI) users and 57 normal hearing (NH) adults (16 in a CI-simulation condition) participated in a visual world paradigm eye-tracking task in which their fixations to a set of phonologically related items were monitored as they heard one item being named. Each degraded-speech group was compared with a set of age-matched NH participants listening to unfiltered speech. CI users and the simulation group showed a delay in activation relative to the NH listeners, and there is weak evidence that the CI users showed differences in the degree of peak and late competitor activation. In general, though, the degraded-speech groups behaved statistically similarly with respect to activation levels.

Functional and structural aging of the speech sensorimotor neural system: functional magnetic resonance imaging evidence

The ability to perceive and produce speech undergoes important changes in late adulthood. The goal of the present study was to characterize functional and structural age-related differences in the cortical network that support speech perception and production, using magnetic resonance imaging, as well as the relationship between functional and structural age-related changes occurring in this network. We asked young and older adults to observe videos of a speaker producing single words (perception), and to observe and repeat the words produced (production). Results show a widespread bilateral network of brain activation for Perception and Production that was not correlated with age. In addition, several regions did show age-related change (auditory cortex, planum temporale, superior temporal sulcus, premotor cortices, SMA-proper). Examination of the relationship between brain signal and regional and global gray matter volume and cortical thickness revealed a complex set of relationships between structure and function, with some regions showing a relationship between structure and function and some not. The present results provide novel findings about the neurobiology of aging and verbal communication.

Spoken word recognition in adolescent cochlear implant users during quiet and multispeaker babble conditions

OBJECTIVE

To assess overall speech intelligibility in adolescent cochlear implant speakers during quiet and multispeaker babble conditions.

STUDY DESIGN

A cross-sectional assessment of intelligibility incorporating group (auditory-oral versus total communication speakers), sentence context (high versus low contexts), and background conditions (quiet versus multispeaker babble).

SETTING

A camp designed to assess adolescents over a concentrated period.

PARTICIPANTS

Fifty-seven adolescents who participated in an earlier study when they were 8 to 9 years old examining functional outcomes of speech perception, speech production, and language were asked to participate in follow-up study.

METHODS

Speech intelligibility was assessed by asking the adolescents to repeat sentences. Sentences were digitally edited and played to normal hearing listeners who either provided broad transcriptions of sound accuracy or wrote down the words they understood when the sentences were presented in quiet and in multispeaker babble.

MAIN OUTCOME VARIABLE

The dependent variables were percent correct consonants, vowels, and total words identified.

RESULTS

Very few substitutions or omissions occurred, resulting in high levels of accuracy for consonants and vowels. Speech intelligibility in quiet was significantly greater than in the multispeaker babble condition. Multispeaker babble decreased performance uniformly across sentence context for the 2 groups.

CONCLUSION

Accurate consonant production based on measures of substitutions and omissions fails to account for distortions and allophonic variations. Reductions in speech intelligibility relative to the phoneme correct productions suggest that the allophonic variations related to distortions may influence naive listener's ability to understand the speech of profoundly deaf individuals.

Vowel spaces in Swedish adolescents with cochlear implants

This paper examines vowel production in Swedish adolescents with cochlear implants. Twelve adolescents with cochlear implants and 11 adolescents with normal hearing participated. Measurements were made of the first and second formants in all the nine long Swedish vowels. The values in hertz were bark-transformed, and two measures of the size of the vowel space were obtained. The first of them was the average Euclidean distance in the F1-F2 plane between the nine vowels and the mean F1 and F2 values of all the vowels. The second was the mean Euclidean distance in the F1-F2 plane between all the vowels. The results showed a significant difference for both vowel space measures between the two groups of adolescents. The cochlear implant users had a smaller space than the adolescents with normal hearing. In general, the size of the vowel space showed no correlations with measures of receptive and productive linguistic abilities. However, the results of an identification test showed that the listeners made more confusions of the vowels produced by speakers who had a small mean distance in the F1-F2 plane between all the vowels.

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

Tongue shape can vary greatly for allophones of /r/ produced in different phonetic contexts but the primary acoustic cue used by listeners, lowered F3, remains stable. For the current study, it was hypothesized that auditory feedback maintains the speech motor control mechanisms that are constraining acoustic variability of F3 in /r/; thus the listener's percept remains /r/ despite the range of articulatory configurations employed by the speaker. Given the potential importance of auditory feedback, postlingually deafened speakers should show larger acoustic variation in /r/ allophones than hearing controls, and auditory feedback from a cochlear implant could reduce that variation over time. To test these hypotheses, measures were made of phoneme perception and of production of tokens containing /r/, stop consonants, and /r/+stop clusters in hearing controls and in eight postlingually deafened adults pre- and postimplant. Postimplant, seven of the eight implant speakers did not differ from the control mean. It was also found that implant users' production of stop and stop+/r/ blend improved with time but the measured acoustic contrast between these was still better in the control speakers than for the implant group even after the implant users had experienced a year of improved auditory feedback.

Audio-vocal system regulation in children with autism spectrum disorders

Do children with autism spectrum disorders (ASD) respond similarly to perturbations in auditory feedback as typically developing (TD) children? Presentation of pitch-shifted voice auditory feedback to vocalizing participants reveals a close coupling between the processing of auditory feedback and vocal motor control. This paradigm was used to test the hypothesis that abnormalities in the audio-vocal system would negatively impact ASD compensatory responses to perturbed auditory feedback. Voice fundamental frequency (F(0)) was measured while children produced an /a/ sound into a microphone. The voice signal was fed back to the subjects in real time through headphones. During production, the feedback was pitch shifted (-100 cents, 200 ms) at random intervals for 80 trials. Averaged voice F(0) responses to pitch-shifted stimuli were calculated and correlated with both mental and language abilities as tested via standardized tests. A subset of children with ASD produced larger responses to perturbed auditory feedback than TD children, while the other children with ASD produced significantly lower response magnitudes. Furthermore, robust relationships between language ability, response magnitude and time of peak magnitude were identified. Because auditory feedback helps to stabilize voice F(0) (a major acoustic cue of prosody) and individuals with ASD have problems with prosody, this study identified potential mechanisms of dysfunction in the audio-vocal system for voice pitch regulation in some children with ASD. Objectively quantifying this deficit may inform both the assessment of a subgroup of ASD children with prosody deficits, as well as remediation strategies that incorporate pitch training.

Effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts

PURPOSE

To assess the effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts and to evaluate hypotheses arising from a model of speech motor planning.

METHOD

The perception and production of vowel and sibilant contrasts were measured in 8 postlingually deafened adults prior to activation of their cochlear implant speech processors, 1 month postactivation, and 1 year postactivation. Measures were taken postactivation both with and without auditory feedback. Contrast measures were also made for a group of speakers with reportedly normal hearing speaking with masked and unmasked auditory feedback.

RESULTS

Vowel and sibilant contrasts, measured in the absence of auditory feedback after 1 month of prosthesis use, were diminished compared with their values measured before prosthesis. Contrasts measured in the absence of auditory feedback after 1 year's experience with the prosthesis were increased compared with their values after 1 month's experience. In both time samples, contrasts were enhanced when auditory feedback was restored.

CONCLUSION

The provision of prosthetic hearing to postlingually deafened adults impaired their phonemic contrasts at first, as their auditory feedback had novel characteristics. Once auditory feedback became recalibrated with prosthesis use, it could, in turn, revise feedforward commands that control the contrasts in its absence.

Effects of auditory feedback deprivation length on the vowel /epsilon/ produced by pediatric cochlear-implant users

Effects of auditory deprivation on speech production by ten cochlear-implanted children were investigated by turning off the implant for durations ranging from 0.3 to 5.0 s and measuring the formant frequencies (F1 and F2) of the vowel /epsilon/. In five of the ten talkers, F1 and/or F2 shifted when auditory feedback was eliminated. Without feedback, F2 frequency lowered consistently, suggesting vowel centralization. Phonetic transcription indicated that some of these acoustic changes led to perceptible shifts in phonetic quality. The results provide evidence that brief periods of auditory deprivation can produce perceptible changes in vowels produced by some cochlear-implanted children.

Time course of speech changes in response to unanticipated short-term changes in hearing state

The timing of changes in parameters of speech production was investigated in six cochlear implant users by switching their implant microphones off and on a number of times in a single experimental session. The subjects repeated four short, two-word utterances, /dV1n#SV2d/ (S = /s/ or /S/), in quasi-random order. The changes between hearing and nonhearing states were introduced by a voice-activated switch at V1 onset. "Postural" measures were made of vowel sound pressure level (SPL), duration, F0; contrast measures were made of vowel separation (distance between pair members in the formant plane) and sibilant separation (difference in spectral means). Changes in parameter values were averaged over multiple utterances, lined up with respect to the switch. No matter whether prosthetic hearing was blocked or restored, contrast measures for vowels and sibilants did not change systematically. Some changes in duration, SPL and F0 were observed during the vowel within which hearing state was changed, V1, as well as during V2 and subsequent utterance repetitions. Thus, sound segment contrasts appear to be controlled differently from the postural parameters of speaking rate and average SPL and F0. These findings are interpreted in terms of the function of hypothesized feedback and feedforward mechanisms for speech motor control.

On the structure of phoneme categories in listeners with cochlear implants

PURPOSE

To describe cochlear implant users' phoneme labeling, discrimination, and prototypes for a vowel and a sibilant contrast, and to assess the effects of 1 year's experience with prosthetic hearing.

METHOD

Based on naturally produced clear examples of "boot," "beet," "said," and "shed" by 1 male and 1 female speaker, continua with 13 stimuli were synthesized for each contrast. Seven hearing controls labeled those stimuli and assigned them goodness ratings, as did 7 implant users at 1-month postimplant. One year later, these measures were repeated, and within category discrimination, d', was assessed.

RESULTS

Compared with controls, implant users' vowel and sibilant labeling slopes were substantially shallower but improved over 1 year of prosthesis use. Their sensitivity to phonetic differences within phoneme categories was about half that of controls. The slopes of their goodness rating functions were shallower and did not improve. Their prototypes for the sibilant contrast (but not the vowels) were closer to one another and did not improve by moving apart.

CONCLUSIONS

Implant users' phoneme labeling and within-category perceptual structure were anomalous at 1-month postimplant. After 1 year of prosthesis use, phoneme labeling categories had sharpened but within category discrimination was well below that of hearing controls.

Effects of masking noise on vowel and sibilant contrasts in normal-hearing speakers and postlingually deafened cochlear implant users

The role of auditory feedback in speech production was investigated by examining speakers' phonemic contrasts produced under increases in the noise to signal ratio (N/S). Seven cochlear implant users and seven normal-hearing controls pronounced utterances containing the vowels /i/, /u/, /e/ and /ae/ and the sibilants /s/ and /I/ while hearing their speech mixed with noise at seven equally spaced levels between their thresholds of detection and discomfort. Speakers' average vowel duration and SPL generally rose with increasing N/S. Average vowel contrast was initially flat or rising; at higher N/S levels, it fell. A contrast increase is interpreted as reflecting speakers' attempts to maintain clarity under degraded acoustic transmission conditions. As N/S increased, speakers could detect the extent of their phonemic contrasts less effectively, and the competing influence of economy of effort led to contrast decrements. The sibilant contrast was more vulnerable to noise; it decreased over the entire range of increasing N/S for controls and was variable for implant users. The results are interpreted as reflecting the combined influences of a clarity constraint, economy of effort and the effect of masking on achieving auditory phonemic goals-with implant users less able to increase contrasts in noise than controls.

Acoustic voice analysis of prelingually deaf adults before and after cochlear implantation

It is widely accepted that many severe to profoundly deaf adults have benefited from cochlear implants (CIs). However, limited research has been conducted to investigate changes in voice and speech of prelingually deaf adults who receive CIs, a population well known for presenting with a variety of voice and speech abnormalities. The purpose of this study was to use acoustic analysis to explore changes in voice and speech for three prelingually deaf males pre- and postimplantation over 6 months. The following measurements, some measured in varying contexts, were obtained: fundamental frequency (F0), jitter, shimmer, noise-to-harmonic ratio, voice turbulence index, soft phonation index, amplitude- and F0-variation, F0-range, speech rate, nasalance, and vowel production. Characteristics of vowel production were measured by determining the first formant (F1) and second formant (F2) of vowels in various contexts, magnitude of F2-variation, and rate of F2-variation. Perceptual measurements of pitch, pitch variability, loudness variability, speech rate, and intonation were obtained for comparison. Results are reported using descriptive statistics. The results showed patterns of change for some of the parameters while there was considerable variation across the subjects. All participants demonstrated a decrease in F0 in at least one context and demonstrated a change in nasalance toward the norm as compared to their normal hearing control. The two participants who were oral-language communicators were judged to produce vowels with an average of 97.2% accuracy and the sign-language user demonstrated low percent accuracy for vowel production.

Adaptive control of vowel formant frequency: evidence from real-time formant manipulation

Auditory feedback during speech production is known to play a role in speech sound acquisition and is also important for the maintenance of accurate articulation. In two studies the first formant (F1) of monosyllabic consonant-vowel-consonant words (CVCs) was shifted electronically and fed back to the participant very quickly so that participants perceived the modified speech as their own productions. When feedback was shifted up (experiment 1 and 2) or down (experiment 1) participants compensated by producing F1 in the opposite frequency direction from baseline. The threshold size of manipulation that initiated a compensation in F1 was usually greater than 60 Hz. When normal feedback was returned, F1 did not return immediately to baseline but showed an exponential deadaptation pattern. Experiment 1 showed that this effect was not influenced by the direction of the F1 shift, with both raising and lowering of F1 exhibiting the same effects. Experiment 2 showed that manipulating the number of trials that F1 was held at the maximum shift in frequency (0, 15, 45 trials) did not influence the recovery from adaptation. There was a correlation between the lag-one autocorrelation of trial-to-trial changes in F1 in the baseline recordings and the magnitude of compensation. Some participants therefore appeared to more actively stabilize their productions from trial-to-trial. The results provide insight into the perceptual control of speech and the representations that govern sensorimotor coordination.

Strength of British English accents in altered listening conditions

This work is concerned with the processing or representational level at which accent forms learned early in life can change and with whether alteration to a speaker's auditory environment can elicit an original accent. In Experiment 1, recordings were made of an equal number of (1) speakers living in the home counties (HC) of Britain (around the London conurbation) who claimed to have retained the accent of the region that they originally had come from, (2) speakers who stated that they had lost their regional accent and acquired an HC accent, and (3) native HC speakers. They read two texts in a normal listening environment. Listeners rated the similarity in accent between each of these texts and all the other texts. The results showed that in the normal listening conditions, the speakers who had lost their accent were rated as being more similar to HC English speakers than to those speakers from the same region who had retained their accent. In Experiment 2, recordings of the same speakers under frequency-shifted and delayed auditory feedback, as well as the normal listening conditions used earlier, were rated in order to see whether the manipulations of listening environment would elicit the speaker's original accent. Listeners rated similarity of accent in a sample of speech recorded under normal listening against a sample read by another speaker in one of the altered listening conditions. When listening condition was altered, the speakers who had lost their original accent were rated as more similar to those who had retained their accent. It is concluded that accent differences can be elicited by altering listening environment because the speech systems of speakers who have lost their accent are more vulnerable than those of speakers who have not changed their original accent.

Compensation following real-time manipulation of formants in isolated vowels

Auditory feedback influences human speech production, as demonstrated by studies using rapid pitch and loudness changes. Feedback has also been investigated using the gradual manipulation of formants in adaptation studies with whispered speech. In the work reported here, the first formant of steady-state isolated vowels was unexpectedly altered within trials for voiced speech. This was achieved using a real-time formant tracking and filtering system developed for this purpose. The first formant of vowel /epsilon/ was manipulated 100% toward either /ae/ or /I/, and participants responded by altering their production with average Fl compensation as large as 16.3% and 10.6% of the applied formant shift, respectively. Compensation was estimated to begin <460 ms after stimulus onset. The rapid formant compensations found here suggest that auditory feedback control is similar for both F0 and formants.

Effects of auditory feedback on fricatives produced by cochlear-implanted adults and children: acoustic and perceptual evidence

Acoustic analyses and perception experiments were conducted to determine the effects of brief deprivation of auditory feedback on fricatives produced by cochlear implant users. The words /si/ and /Si/ were recorded by four children and four adults with their cochlear implant speech processor turned on or off. In the processor-off condition, word durations increased significantly for a majority of talkers. These increases were greater for children compared to adults, suggesting that children may rely on auditory feedback to a greater extent than adults. Significant differences in spectral measures of /S/ were found between processor-on and processor-off conditions for two of the four children and for one of the four adults. These talkers also demonstrated a larger /s/-/S/ contrast in centroid values compared to the other talkers within their respective groups. This finding may indicate that talkers who produce fine spectral distinctions are able to perceive these distinctions through their implants and to use this feedback to fine tune their speech. Two listening experiments provided evidence that some of the acoustic changes were perceptible to normal-hearing listeners. Taken together, these experiments indicate that for certain cochlear-implant users the brief absence of auditory feedback may lead to perceptible modifications in fricative consonants.

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.

Reception of Environmental Sounds Through Cochlear Implants

OBJECTIVE

The objective of this study was to measure the performance of persons with cochlear implants on a test of environmental-sound reception.

DESIGN

The reception of environmental sounds was studied using a test employing closed sets of 10 sounds in each of four different settings (General Home, Kitchen, Office, and Outside). The participants in the study were 11 subjects with cochlear implants. Identification testing was conducted under each of the four closed sets of stimuli using a one-interval, 10-alternative, forced-choice procedure. The data were summarized in terms of overall percent correct identification scores and information transfer (IT) in bits. Confusion patterns were described using a hierarchical-clustering analysis. In addition, individual performance on the environmental-sound task was related to the ability to recognize isolated words through the cochlear implant alone.

RESULTS

Levels of performance were similar across the four stimulus sets. Mean scores across subjects ranged from 45.3% correct (and IT of 1.5 bits) to 93.8% correct (and IT of 3.1 bits). Performance on the environmental-sound identification test was roughly related to NU-6 word recognition ability. Specifically, those subjects with word scores greater than 34% correct performed at levels of 80 to 94% on environmental-sound recognition, whereas subjects with word scores less than 34% had greater difficulty on the task. Results of the hierarchical clustering analysis, conducted on two groups of subjects (a high-performing [HP] group and a low-performing [LP] group), indicated that confusions were confined to three or four specific stimuli for the HP subjects and that larger clusters of confused stimuli were observed in the data of the LP group. Signals with distinct temporal-envelope characteristics were easily perceived by all subjects, and confused items tended to share similar overall durations and temporal envelopes.

CONCLUSIONS

Temporal-envelope cues appear to play a large role in the identification of environmental sounds through cochlear implants. The finer distinctions made by the HP group compared with the LP group may be related to a better ability both to resolve temporal differences and to use gross spectral cues. These findings are qualitatively consistent with patterns of confusions observed in the reception of speech segments through cochlear implants.

The distinctness of speakers' /s/-/S/ contrast is related to their auditory discrimination and use of an articulatory saturation effect

This study examines individual differences in producing the sibilant contrast in American English and the relation of those differences to 2 speaker characteristics: (a) use of a quantal biomechanical effect (called a "saturation effect") in producing the sibilants and (b) performance on a test of sibilant discrimination. Twenty participants produced the sibilants /s/ and /S/ in normal-, clear-, and fast-speaking conditions. The degree to which the participants used a saturation effect in producing /s/ and /S/ was assessed with a custom-made sensor that measured contact of the underside of the tongue tip with the lower alveolar ridge; such contact normally occurs during the production of /s/ but not /S/. The acuteness of the participants' discrimination of the sibilant contrast was measured using the ABX paradigm and synthesized sibilants. Differences among speakers in the degree of acoustic contrast between /s/ and /S/ that they produced proved related to differences among them in their use of contact contrastively and in their discriminative performance. The most distinct sibilant productions were obtained from participants who used contact in producing /s/ but not /S/ and who had high discrimination scores. The participants who did not use contact differentially when producing the 2 sibilants and who also discriminated the synthetic sibilants less well produced the least distinct sibilant contrasts. Intermediate degrees of sibilant contrast were found with participants who used contact differentially or discriminated well. These findings are compatible with a model of speech motor planning in which goals for phonemic speech movements are in somatosensory and auditory spaces.

Effect of the loss of auditory feedback on segmental parameters of vowels of postlingually deafened speakers

OBJECTIVE

The most obvious and best documented changes in speech of postlingually deafened speakers are the rate, fundamental frequency, and volume (energy). These changes are due to the lack of auditory feedback. But auditory feedback affects not only the suprasegmental parameters of speech. The aim of this study was to determine the change at the segmental level of speech in terms of vowel formants.

METHODS

Twenty-three postlingually deafened and 18 normally hearing speakers were recorded reading a German text. The frequencies of the first and second formants and the vowel spaces of selected vowels in word-in-context condition were compared.

RESULTS

All first formant frequencies (F1) of the postlingually deafened speakers were significantly different from those of the normally hearing people. The values of F1 were higher for the vowels /e/ (418+/-61 Hz compared with 359+/-52 Hz, P=0.006) and /o/ (459+/-58 compared with 390+/-45 Hz, P=0.0003) and lower for /a/ (765+/-115 Hz compared with 851+/-146 Hz, P=0.038). The second formant frequency (F2) only showed a significant increase for the vowel/e/(2016+/-347 Hz compared with 2279+/-250 Hz, P=0.012). The postlingually deafened people were divided into two subgroups according to duration of deafness (shorter/longer than 10 years of deafness). There was no significant difference in formant changes between the two groups.

CONCLUSION

Our report demonstrated an effect of auditory feedback also on segmental features of speech of postlingually deafened people.

Acoustic analysis of monophthong and diphthong production in acquired severe to profound hearing loss

The effect of diminished auditory feedback on monophthong and diphthong production was examined in postlingually deafened Australian-English speaking adults. The participants were 4 female and 3 male speakers with severe to profound hearing loss, who were compared to 11 age- and accent-matched normally hearing speakers. The test materials were 5 repetitions of hVd words containing 18 vowels. Acoustic measures that were studied included F1, F2, discrete cosine transform coefficients (DCTs), and vowel duration information. The durational analyses revealed increased total vowel durations with a maintenance of the tense/lax vowel distinctions in the deafened speakers. The deafened speakers preserved a differentiated vowel space, although there were some gender-specific differences seen. For example, there was a retraction of F2 in the front vowels for the female speakers that did not occur in the males. However, all deafened speakers showed a close correspondence between the monophthong and diphthong formant movements that did occur. Gaussian classification highlighted vowel confusions resulting from changes in the deafened vowel space. The results support the view that postlingually deafened speakers maintain reasonably good speech intelligibility, in part by employing production strategies designed to bolster auditory feedback.

Stability of memory traces for speech sounds in cochlear implant patients

For this study, we examined the perception and production of vowels by postlingually deafened patients with cochlear implant. Four patients and one normally hearing subject produced typical vowel sounds of Finnish by using a speech synthesizer. Also acoustic analyses of the pronounced vowels were made. The first (F1) and the second (F2) formant frequencies were measured. The mismatch negativity (MMN), a cortical cognitive auditory event related potential, was used to measure objectively the patients' preattentive discrimination of a prototypical /i/ sound from deviants differing in the F2 continuum. In the phonetic tests the hyperspace effect was seen also among the patients. The MMN, which reflects the phonetic discrimination ability, could be identified from the patient with the best vowel perception abilities. The phonetic memory traces once developed for vowels seem to remain quite stable even though they have not been activated by vowel information for years.

Changes in speech intelligibility of postlingually deaf adults after cochlear implantation

OBJECTIVE

This study examines changes in the intelligibility of CVC words spoken by postlingually deafened adults after they have had 6 to 12 mo of experience with a cochlear implant. The hypothesis guiding the research is that the intelligibility of these speakers will improve after extended use of a cochlear implant. The paper also describes changes in CVC word intelligibility analyzed by phoneme class and by features.

DESIGN

The speech of eight postlingually deaf adults was recorded before activation of the speech processors of their cochlear implants and at 6 mo and 1 yr after activation. Seventeen listeners with no known impairment of hearing completed a word identification task while listening to each implant user's speech in noise. The percent information transmitted by the speakers in their pre- and postactivation recordings was measured for 11 English consonants and eight vowels separately.

RESULTS

An overall improvement in word intelligibility was observed: seven of the eight speakers showed improvement in vowel intelligibility and six speakers showed improvement in consonant intelligibility. However, the intelligibility of specific consonant and vowel features varied greatly across speakers.

CONCLUSIONS

Extended use of a cochlear implant by postlingually deafened adults tends to enhance their intelligibility.

Language-specific, hearing-related changes in vowel spaces: a preliminary study of English- and Spanish-speaking cochlear implant users

OBJECTIVE

This study investigates the role of hearing in vowel productions of postlingually deafened cochlear implant users. Two hypotheses are tested that derive from the view that vowel production is influenced by competing demands of intelligibility for the listener and least effort in the speaker: 1) Hearing enables a cochlear implant user to produce vowels distinctly from one another; without hearing, the speaker may give more weight to economy of effort, leading to reduced vowel separation. 2) Speakers may need to produce vowels more distinctly from one another in a language with a relatively "crowded" vowel space, such as American English, than in a language with relatively few vowels, such as Spanish. Thus, when switching between hearing and non-hearing states, English speakers may show a tradeoff between vowel distinctiveness and least effort, whereas Spanish speakers may not.

DESIGN

To test the prediction that there will be a reduction of average vowel spacing (AVS) (average intervowel distance in the F1-F2 plane) with interrupted hearing for English-speaking cochlear implant users, but no systematic change in AVS for Spanish cochlear implant users, vowel productions of seven English-speaking and seven Spanish-speaking cochlear implant users, who had been using their implants for at least 1 yr, were recorded when their implant speech processors were turned off and on several times in two sessions.

RESULTS

AVS was consistently larger for the English speakers with hearing than without hearing. The magnitude and direction of AVS change was more variable for the Spanish speakers, both within and between subjects.

CONCLUSION

Vowel distinctiveness was enhanced with the provision of some hearing in the language group with a more crowded vowel space but not in the language group with fewer vowels. The view that speakers seek to minimize effort while maintaining the distinctiveness of acoustic goals receives some support.

Covariation of cochlear implant users' perception and production of vowel contrasts and their identification by listeners with normal hearing

This study investigates covariation of perception and production of vowel contrasts in speakers who use cochlear implants and identification of those contrasts by listeners with normal hearing. Formant measures were made of seven vowel pairs whose members are neighboring in acoustic space. The vowels were produced in carrier phrases by 8 postlingually deafened adults, before and after they received their cochlear implants (CI). Improvements in a speaker's production and perception of a given vowel contrast and normally hearing listeners' identification of that contrast in masking noise tended to occur together. Specifically, speakers who produced vowel pairs with reduced contrast in the pre-CI condition (measured by separation in the acoustic vowel space) and who showed improvement in their perception of these contrasts post-CI (measured with a phoneme identification test) were found to have enhanced production contrasts post-CI in many cases. These enhanced production contrasts were associated, in turn, with enhanced masked word recognition, as measured from responses of a group of 10 normally hearing listeners. The results support the view that restoring self-hearing allows a speaker to adjust articulatory routines to ensure sufficient perceptual contrast for listeners.