Detection of dead regions in the cochlea: relevance for combined electric and acoustic stimulation

A computational model to simulate spectral modulation and speech perception experiments of cochlear implant users

Speech understanding in cochlear implant (CI) users presents large intersubject variability that may be related to different aspects of the peripheral auditory system, such as the electrode–nerve interface and neural health conditions. This variability makes it more challenging to proof differences in performance between different CI sound coding strategies in regular clinical studies, nevertheless, computational models can be helpful to assess the speech performance of CI users in an environment where all these physiological aspects can be controlled. In this study, differences in performance between three variants of the HiRes Fidelity 120 (F120) sound coding strategy are studied with a computational model. The computational model consists of (i) a processing stage with the sound coding strategy, (ii) a three-dimensional electrode-nerve interface that accounts for auditory nerve fiber (ANF) degeneration, (iii) a population of phenomenological ANF models, and (iv) a feature extractor algorithm to obtain the internal representation (IR) of the neural activity. As the back-end, the simulation framework for auditory discrimination experiments (FADE) was chosen. Two experiments relevant to speech understanding were performed: one related to spectral modulation threshold (SMT), and the other one related to speech reception threshold (SRT). These experiments included three different neural health conditions (healthy ANFs, and moderate and severe ANF degeneration). The F120 was configured to use sequential stimulation (F120-S), and simultaneous stimulation with two (F120-P) and three (F120-T) simultaneously active channels. Simultaneous stimulation causes electric interaction that smears the spectrotemporal information transmitted to the ANFs, and it has been hypothesized to lead to even worse information transmission in poor neural health conditions. In general, worse neural health conditions led to worse predicted performance; nevertheless, the detriment was small compared to clinical data. Results in SRT experiments indicated that performance with simultaneous stimulation, especially F120-T, were more affected by neural degeneration than with sequential stimulation. Results in SMT experiments showed no significant difference in performance. Although the proposed model in its current state is able to perform SMT and SRT experiments, it is not reliable to predict real CI users' performance yet. Nevertheless, improvements related to the ANF model, feature extraction, and predictor algorithm are discussed.

Perceived listening effort in children with hearing loss: listening to a dysphonic voice in quiet and in noise

AIM

The present study investigates the effect of signal degradation on perceived listening effort in children with hearing loss listening in a simulated class-room context. It also examines the associations between perceived listening effort, passage comprehension performance and executive functioning.

METHODS

Twenty-four children (aged 06:03-13:00 years) with hearing impairment using cochlear implant (CI) and/or hearing aids (HA) participated. The children made ratings of perceived listening effort after completing an auditory passage comprehension task. All children performed the task in four different listening conditions: listening to a typical (i.e. normal) voice in quiet, to a dysphonic voice in quiet, to a typical voice in background noise and to a dysphonic voice in background noise. In addition, the children completed a task assessing executive function.

RESULTS

Both voice quality and background noise increased perceived listening effort in children with CI/HA, but no interaction with executive function was seen.

CONCLUSION

Since increased listening effort seems to be a consequence of increased cognitive resource spending, it is likely that less resources will be available for these children not only to comprehend but also to learn in challenging listening environments such as classrooms.

Comparing Rapid and Traditional Forward-Masked Spatial Tuning Curves in Cochlear-Implant Users

A rapid forward-masked spatial tuning curve measurement procedure, based on Bekesy tracking, was adapted and evaluated for use with cochlear implants. Twelve postlingually-deafened adult cochlear-implant users participated. Spatial tuning curves using the new procedure and using a traditional forced-choice adaptive procedure resulted in similar estimates of parameters. The Bekesy-tracking method was almost 3 times faster than the forced-choice procedure, but its test-retest reliability was significantly poorer. Although too time-consuming for general clinical use, the new method may have some benefits in individual cases, where identifying electrodes with poor spatial selectivity as candidates for deactivation is deemed necessary.

Passage comprehension performance in children with cochlear implants and/or hearing aids: the effects of voice quality and multi-talker babble noise in relation to executive function

Purpose: Speech signal degradation such as a voice disorder presented in quiet or in combination with multi-talker babble noise could affect listening comprehension in children with hearing impairment. This study aims to investigate the effects of voice quality and multi-talker babble noise on passage comprehension in children with using cochlear implants (CIs) and/or hearing aids (HAs). It also aims to examine what role executive functioning has for passage comprehension in listening conditions with degraded signals (voice quality and multi-talker babble noise) in children using CI/HA. Methods: Twenty-three children (10 boys and 13 girls; mean age 9 years) using CI and/or HA were tested for passage comprehension in four listening conditions: a typical voice or a (hoarse) dysphonic, voice presented in quiet or in multi-talker babble noise. Results: The results show that the dysphonic voice did not affect passage comprehension in quiet or in noise. Multi-talker babble noise decreased passage comprehension compared to performance in quiet. No interactions with executive function were found. Conclusions: In conclusion, children with CI/HA seem to struggle with comprehension in poor sound environments, which in turn may reduce learning opportunities at school.

A Hearing-Model-Based Active-Learning Test for the Determination of Dead Regions

This article describes a Bayesian active-learning procedure for estimating the edge frequency, f_e, of a dead region, that is, a region in the cochlea with no or very few functioning inner hair cells or neurons. The method is based on the psychophysical tuning curve (PTC) but estimates the shape of the PTC from the parameters of a hearing model, namely f_e, and degree of outer hair cell loss. It chooses the masker frequency and level for each trial to be highly informative about the model parameters in the context of previous data. The procedure was tested using 14 ears from eight subjects previously diagnosed with high-frequency dead regions. The estimates of f_e agreed well with estimates obtained using “Fast PTCs” or more extensive measurements from an earlier study. On average, 33 trials were needed for the estimate of f_e to fall and stay within 0.3 Cams of the final “true” value on the equivalent rectangular bandwidth-number scale. The time needed to obtain a reliable estimate was 5 to 8 min. This is comparable to the time required for Fast PTCs and short enough to be used when fitting a hearing aid. Compared with Fast PTCs, the new method has the advantage of using yes-no judgments rather than continuous Békésy tracking. This allows the slope of a subject’s psychometric function and thus the reliability of his or her responses to be estimated, which in turn allows the test duration to be adjusted so as to achieve a given accuracy.

Reference thresholds for the TEN(HL) test for people with normal hearing

OBJECTIVE

To estimate normative values and repeatability of thresholds for the TEN(HL) test for diagnosing dead regions in the cochlea, as a function of signal frequency, TEN(HL) level, age and gender.

DESIGN

The TEN(HL) test was administered twice for each ear of each participant using signal frequencies from 0.5 to 4 kHz and TEN(HL) levels of 30, 50 and 70 dB HL/ERB_N.

STUDY SAMPLE

In all, 29 young participants and 8 older participants were tested. All had normal audiograms with no history of hearing problems.

RESULTS

There was good repeatability across sessions. There was no significant effect of ear, gender or age group. The average signal-to-TEN ratio (STR) at threshold was close to 0 dB. For low signal frequencies, the STR at threshold varied only slightly with TEN(HL) level, but for the signal frequencies of 3 and 4 kHz the STR at threshold increased to about +2.7 dB for the TEN(HL) level of 70 dB/ERB_N.

CONCLUSIONS

For a high TEN(HL) level, the "normal" STR at threshold at 3 and 4 kHz is closer to +2 dB than to 0 dB. Further research is needed to assess whether the TEN(HL)-test criteria need to be modified when testing at high frequencies and high levels.

[Pathophysiology of hearing loss : Classification and treatment options]

From the therapeutic perspective, the etiology and pathophysiology of hearing loss can be classified based on the extent of the primary cause. Hearing loss can have very different consequences for cell preservation in the organ of Corti and the spiral ganglion. These not only have implications for prosthetic therapy outcome, but may also influence the potential for future causal molecular therapies. Etiologies leading to deficits that are limited to one or a few molecules without having an effect on cell survival have the greatest potential for future causal therapy using molecular and cellular approaches. Preliminary success for molecular therapy was recently reported in animal experiments. Unfortunately, the incidence of these types of hearing loss is very low and in the future the therapy of hearing loss will therefore also require several different approaches. In addition to peripheral pathophysiology, hearing loss has consequences on the functioning of the brain, which can vary greatly due to individual adaptation to the situation without hearing. The authors therefore argue for individualization of the diagnostics and therapy that focus not only the symptom of hearing loss, but also the individual pathophysiology and consequences. Only with individualized therapy can the success of treating hearing disorders be significantly improved.

Auditory implant research at the House Ear Institute 1989-2013

The House Ear Institute (HEI) had a long and distinguished history of auditory implant innovation and development. Early clinical innovations include being one of the first cochlear implant (CI) centers, being the first center to implant a child with a cochlear implant in the US, developing the auditory brainstem implant, and developing multiple surgical approaches and tools for Otology. This paper reviews the second stage of auditory implant research at House - in-depth basic research on perceptual capabilities and signal processing for both cochlear implants and auditory brainstem implants. Psychophysical studies characterized the loudness and temporal perceptual properties of electrical stimulation as a function of electrical parameters. Speech studies with the noise-band vocoder showed that only four bands of tonotopically arrayed information were sufficient for speech recognition, and that most implant users were receiving the equivalent of 8-10 bands of information. The noise-band vocoder allowed us to evaluate the effects of the manipulation of the number of bands, the alignment of the bands with the original tonotopic map, and distortions in the tonotopic mapping, including holes in the neural representation. Stimulation pulse rate was shown to have only a small effect on speech recognition. Electric fields were manipulated in position and sharpness, showing the potential benefit of improved tonotopic selectivity. Auditory training shows great promise for improving speech recognition for all patients. And the Auditory Brainstem Implant was developed and improved and its application expanded to new populations. Overall, the last 25 years of research at HEI helped increase the basic scientific understanding of electrical stimulation of hearing and contributed to the improved outcomes for patients with the CI and ABI devices. This article is part of a Special Issue entitled .

Relationship between age of hearing-loss onset, hearing-loss duration, and speech recognition in individuals with severe-to-profound high-frequency hearing loss

The factors responsible for interindividual differences in speech-understanding ability among hearing-impaired listeners are not well understood. Although audibility has been found to account for some of this variability, other factors may play a role. This study sought to examine whether part of the large interindividual variability of speech-recognition performance in individuals with severe-to-profound high-frequency hearing loss could be accounted for by differences in hearing-loss onset type (early, progressive, or sudden), age at hearing-loss onset, or hearing-loss duration. Other potential factors including age, hearing thresholds, speech-presentation levels, and speech audibility were controlled. Percent-correct (PC) scores for syllables in dissyllabic words, which were either unprocessed or lowpass filtered at cutoff frequencies ranging from 250 to 2,000 Hz, were measured in 20 subjects (40 ears) with severe-to-profound hearing losses above 1 kHz. For comparison purposes, 20 normal-hearing subjects (20 ears) were also tested using the same filtering conditions and a range of speech levels (10-80 dB SPL). Significantly higher asymptotic PCs were observed in the early (<=4 years) hearing-loss onset group than in both the progressive- and sudden-onset groups, even though the three groups did not differ significantly with respect to age, hearing thresholds, or speech audibility. In addition, significant negative correlations between PC and hearing-loss onset age, and positive correlations between PC and hearing-loss duration were observed. These variables accounted for a greater proportion of the variance in speech-intelligibility scores than, and were not significantly correlated with, speech audibility, as quantified using a variant of the articulation index. Although the lack of statistical independence between hearing-loss onset type, hearing-loss onset age, hearing-loss duration, and age complicate and limit the interpretation of the results, these findings indicate that other variables than audibility can influence speech intelligibility in listeners with severe-to-profound high-frequency hearing loss.