Evaluation of Two Spectro-Temporal Ripple Tests and Their Relation to the Matrix Speech-in-Noise Sentence Test in Cochlear Implant Recipients.

OBJECTIVES: Spectro-temporal ripple tests are commonly used in cochlear implant (CI) research as language-independent indicators of speech recognition (in noise) or as stand-alone tests. Test-retest reliability of these tests has been scarcely documented. We evaluated the test-retest reliability of spectral-temporally modulated ripple test (SMRT) and spectro-temporal ripple for investigating processor effectiveness (STRIPES) and correlated their findings to the Dutch/Flemish Matrix speech-in-noise sentence test (MST) in CI recipients. This is the first time spectro-temporal ripple tests are correlated to an MST. DESIGN: Take-home data from 15 participants over 2 test days were analyzed. Participants were fitted with their clinical speech encoding strategy (Advanced Bionics HiRes Optima) or a 14-channel non-steered monopolar strategy. Test-retest reliability was calculated through intraclass correlation coefficients and visualized through Bland Altman plots. Association of the spectro-temporal ripple tests with the MST was evaluated through linear regression analysis. RESULTS: The SMRT and STRIPES possessed a similarly rated "good" test-retest reliability (SMRT: ICC = 0.81, confidence interval = 0.67 to 0.92; STRIPES: ICC = 0.87, confidence interval = 0.76 to 0.95) and an identical linear relationship to speech recognition in noise (SMRT: R2 = 0.28, p = 0.04; STRIPES: R2 = 0.28, p = 0.04). Both tests revealed a stable variability between session 1 and 2 outcome scores on Bland Altman plots. CONCLUSION: On the basis of our data, both spectro-temporal ripple tests possess similar test-retest reliability and a similar association with the MST. The SMRT and STRIPES can therefore both be used equally well as a quick indicator of across-listener differences in speech recognition in noise in CI recipients.

Benefit of contralateral routing of signals for unilateral cochlear implant users.

One way to improve speech understanding in noise for HI with a unilateral hearing loss is by contralateral routing of signals (CROS). Such a CROS-system captures sounds with an additional microphone at the worst hearing ear and transmits these to the better one. The better ear is then provided with a mix of signals originating from both ears. The goal of this study is to quantify the effect of a CROS-system on speech reception thresholds (SRTs) with unilaterally implanted CI-users in diffuse and directional noise as a function of speaker location. Listening tests are performed and an accurate directional intelligibly model is proposed used for further analysis. In diffuse noise it is concluded that the use of a CROS system results in a maximum gain in SRT of 7.9 dB when speech comes from the CROS side compared to a maximum loss in SRT of 2.1 dB when speech comes from the implanted side. In the case of directional noise, the effect of the CROS is symmetric and the maximum loss or gain in SRT was around 9 dB. The study therefore shows a clear potential of using the CROS system in diffuse noise.

The Temporal Fine Structure of Background Noise Determines the Benefit of Bimodal Hearing for Recognizing Speech.

Cochlear implant (CI) users have more difficulty understanding speech in temporally modulated noise than in steady-state (SS) noise. This is thought to be caused by the limited low-frequency information that CIs provide, as well as by the envelope coding in CIs that discards the temporal fine structure (TFS). Contralateral amplification with a hearing aid, referred to as bimodal hearing, can potentially provide CI users with TFS cues to complement the envelope cues provided by the CI signal. In this study, we investigated whether the use of a CI alone provides access to only envelope cues and whether acoustic amplification can provide additional access to TFS cues. To this end, we evaluated speech recognition in bimodal listeners, using SS noise and two amplitude-modulated noise types, namely babble noise and amplitude-modulated steady-state (AMSS) noise. We hypothesized that speech recognition in noise depends on the envelope of the noise, but not on its TFS when listening with a CI. Secondly, we hypothesized that the amount of benefit gained by the addition of a contralateral hearing aid depends on both the envelope and TFS of the noise. The two amplitude-modulated noise types decreased speech recognition more effectively than SS noise. Against expectations, however, we found that babble noise decreased speech recognition more effectively than AMSS noise in the CI-only condition. Therefore, we rejected our hypothesis that TFS is not available to CI users. In line with expectations, we found that the bimodal benefit was highest in babble noise. However, there was no significant difference between the bimodal benefit obtained in SS and AMSS noise. Our results suggest that a CI alone can provide TFS cues and that bimodal benefits in noise depend on TFS, but not on the envelope of the noise.

Short and long-term adaptation in the auditory nerve stimulated with high-rate electrical pulse trains are better described by a power law.

Despite the introduction of many new sound-coding strategies speech perception outcomes in cochlear implant listeners have leveled off. Computer models may help speed up the evaluation of new sound-coding strategies, but most existing models of auditory nerve responses to electrical stimulation include limited temporal detail, as the effects of longer stimulation, such as adaptation, are not well-studied. Measured neural responses to stimulation with both short (400 ms) and long (10 min) duration high-rate (5kpps) pulse trains were compared in terms of spike rate and vector strength (VS) with model outcomes obtained with different forms of adaptation. A previously published model combining biophysical and phenomenological approaches was adjusted with adaptation modeled as a single decaying exponent, multiple exponents and a power law. For long duration data, power law adaptation by far outperforms the single exponent model, especially when it is optimized per fiber. For short duration data, all tested models performed comparably well, with slightly better performance of the single exponent model for VS and of the power law model for the spike rates. The power law parameter sets obtained when fitted to the long duration data also yielded adequate predictions for short duration stimulation, and vice versa. The power law function can be approximated with multiple exponents, which is physiologically more viable. The number of required exponents depends on the duration of simulation; the 400 ms data was well-replicated by two exponents (23 and 212 ms), whereas the 10-minute data required at least seven exponents (ranging from 4 ms to 600 s). Adaptation of the auditory nerve to high-rate electrical stimulation can best be described by a power-law or a sum of exponents. This gives an adequate fit for both short and long duration stimuli, such as CI speech segments.

Effect of neural adaptation and degeneration on pulse-train ECAPs: A model study.

Electrically evoked compound action potentials (eCAPs) are measurements of the auditory nerve's response to electrical stimulation. ECAP amplitudes during pulse trains can exhibit temporal alternations. The magnitude of this alternation tends to diminish over time during the stimulus. How this pattern relates to the temporal behavior of nerve fibers is not known. We hypothesized that the stochasticity, refractoriness, adaptation of the threshold and spike-times influence pulse-train eCAP responses. Thirty thousand auditory nerve fibers were modeled in a three-dimensional cochlear model incorporating pulse-shape effects, pulse-history effects, and stochasticity in the individual neural responses. ECAPs in response to pulse trains of different rates and amplitudes were modeled for fibers with different stochastic properties (by variation of the relative spread) and different temporal properties (by variation of the refractory periods, adaptation and latency). The model predicts alternation of peak amplitudes similar to available human data. In addition, the peak alternation was affected by changing the refractoriness, adaptation, and relative spread of auditory nerve fibers. As these parameters are related to factors such as the duration of deafness and neural survival, this study suggests that the eCAP pattern in response to pulse trains could be used to assess the underlying temporal and stochastic behavior of the auditory nerve. As these properties affect the nerve's response to pulse trains, they are of uttermost importance to sound perception with cochlear implants.

[Permanent hearing loss in the prelingual phase in children with a non-aberrant neonatal hearing screening result]. / Permanent gehoorverlies in de prelinguale fase bij kinderen met een niet-afwijkende uitslag bij neonatale gehoorscreening.

--Neonatal hearing screening is fully implemented in the Netherlands since June 2006 using otoacoustic emissions (OAE) and automated auditory brainstem response (AABR) technology. --A normal neonatal hearing screening result unfortunately does not guarantee childhood normal hearing. Hearing loss may not become manifest until after the neonatal period. --Hearing loss at a later stage may be classified in three categories: (a) delayed onset hearing loss which occurs when the cause of the hearing loss is present at birth but the hearing loss itself becomes detectable at a later stage; (b) progressive hearing loss in which a very slight hearing loss may be present at birth but is not yet detectable and the hearing loss becomes progressively more severe; and (c) acquired hearing loss that results from a number of external factors, such as meningitis, ototoxic drugs, neonatal hyperbilirubinaemia necessitating an exchange transfusion, and trauma. --Neonatal hearing screening can result in detection of moderate to profound permanent hearing loss at an early age when therapeutic options may have maximum effect. However, even after this period, constant vigilance is necessary to detect permanent hearing loss in young children, especially during the prelingual period.

Modeled auditory nerve responses to amplitude modulated cochlear implant stimulation.

Cochlear implants encode speech information by stimulating the auditory nerve with amplitude-modulated pulse trains. A computer model of the auditory nerve's response to electrical stimulation can be used to evaluate different approaches to improving CI patients' perception. In this paper a computationally efficient stochastic and adaptive auditory nerve model was used to investigate full nerve responses to amplitude-modulated electrical pulse trains. The model was validated for nerve responses to AM pulse trains via comparison with animal data. The influence of different parameters, such as adaptation and stochasticity, on long-term adaptation and modulation-following behavior was investigated. Responses to pulse trains with different pulse amplitudes, amplitude modulation frequencies, and modulation depths were modeled. Rate responses as well as period histograms, Vector Strength and the fundamental frequency were characterized in different time bins. The response alterations, including frequency following behavior, observed over the stimulus duration were similar to those seen in animal experiments. The tested model can be used to predict complete nerve responses to arbitrary input, and thus to different sound coding strategies.

A fast, stochastic, and adaptive model of auditory nerve responses to cochlear implant stimulation.

Cochlear implants (CIs) rehabilitate hearing impairment through direct electrical stimulation of the auditory nerve. New stimulation strategies can be evaluated using computational models. In this study, a computationally efficient model that accurately predicts auditory nerve responses to CI pulse train input was developed. A three-dimensional volume conduction and active nerve model developed at Leiden University Medical Center was extended with stochasticity, adaptation, and accommodation. This complete model includes spatial and temporal characteristics of both the cochlea and the auditory nerve. The model was validated by comparison with experimentally measured single fiber action potential responses to pulse trains published in the literature. The effects of pulse rate and pulse amplitude on spiking patterns were investigated. The modeled neural responses to CI stimulation were very similar to the single fiber action potential measurements in animal experiments. The model's responses to pulse train stimulation with respect to spatial location were also investigated. Adaptation was stronger at the borders of the stimulated area than in the center. By combining spatial details with long-term temporal components and a broad implementation of stochasticity a comprehensive model was developed that was validated for long duration electric stimulation of a wide range of pulse rates and amplitudes. The model can be used to evaluate auditory nerve responses to cochlear implant sound coding strategies.

Visualization of human inner ear anatomy with high-resolution MR imaging at 7T: initial clinical assessment.

BACKGROUND AND PURPOSE: In many centers, MR imaging of the inner ear and auditory pathway performed on 1.5T or 3T systems is part of the preoperative work-up of cochlear implants. We investigated the applicability of clinical inner ear MR imaging at 7T and compared the visibility of inner ear structures and nerves within the internal auditory canal with images acquired at 3T. MATERIALS AND METHODS: Thirteen patients with sensorineural hearing loss eligible for cochlear implantation underwent examinations on 3T and 7T scanners. Two experienced head and neck radiologists evaluated the 52 inner ear datasets. Twenty-four anatomic structures of the inner ear and 1 overall score for image quality were assessed by using a 4-point grading scale for the degree of visibility. RESULTS: The visibility of 11 of the 24 anatomic structures was rated higher on the 7T images. There was no significant difference in the visibility of 13 anatomic structures and the overall quality rating. A higher incidence of artifacts was observed in the 7T images. CONCLUSIONS: The gain in SNR at 7T yielded a more detailed visualization of many anatomic structures, especially delicate ones, despite the challenges accompanying MR imaging at a high magnetic field.

Field patterns in a 3D tapered spiral model of the electrically stimulated cochlea.

Despite the fact that cochlear implants are widely and successfully used in clinical practice, relatively little is known to date about the electric field patterns they set up in the cochlea. Based upon the available measurements and modelling results, the scala tympani is usually considered to be a preferential current pathway that acts like a leaky transmission line. Therefore, most authors assume the current thresholds to decay exponentially along the length of the scala tympani. Here we present potential distributions calculated with a fully three-dimensional, spiralling volume conduction model of the guinea pig cochlea, and try to identify its preferential current pathways. The relatively well conducting scala tympani turns out to be the main one indeed, but the exponential decay (J approximately e(-z)) of current is only a good description of the far-field behaviour. In the vicinity of the electrodes, i.e. near the fibres that are most easily excited, higher current densities are found, that are best described by a spherical spread of the current (J approximately 1/R(2)). The results are compared with those obtained with a variant of our previous, rotationally symmetric, model and with measurements in the literature. The implications of the findings are discussed in the light of simulated neural responses.

The importance of human cochlear anatomy for the results of modiolus-hugging multichannel cochlear implants.

HYPOTHESIS: The fact that the anatomy of the basal turn of the human cochlea, especially, is essentially different from that of other species is likely to influence the outcome of cochlear implantation. BACKGROUND: Multichannel cochlear implants give better speech understanding than single-channel devices. They are intended to make use of the tonotopic organization of the cochlea by selectively stimulating subpopulations of the auditory nerve. At higher stimulus levels and with monopolar stimulation, excitation of nerve fibers from other turns may interfere with this concept, especially with modiolus-hugging electrodes. METHODS: A three-dimensional spiraling computer model of the human cochlea, based on histologic data, was used to test the spatial selectivity and the dynamic range before cross-turn stimulation takes place for the Clarion HiFocus implant with and without a positioner. The results were compared with a similar model of the guinea pig cochlea. RESULTS: In humans (in contrast to the guinea pig), a well-designed modiolus-hugging electrode yielded reduced current thresholds and high spatial selectivity without reduction of the useful dynamic range. The apical turn of the human cochlea, however, is largely comparable in this respect with the guinea pig cochlea, where cross-turn stimulation reduces the dynamic range substantially. CONCLUSION: The clinical success of cochlear implantation in humans and the favorable results with modiolus-hugging devices depend on the anatomy of the human cochlea.

Evaluation of voice quality in adductor spasmodic dysphonia before and after botulinum toxin treatment.

In this prospective study, the efficacy of botulinum toxin (Botox) injections in patients with adductor spasmodic dysphonia (AdSD) was assessed by 3 different modalities: perceptual and acoustic analyses and subjective self-assessment. This was done by comparing AdSD patients' pretreatment and posttreatment values and comparing these values with those of normal control speakers. In contrast to most other studies, the posttreatment status was defined as the optimal voice quality as judged by the patient. The aim of the study was to assess to what extent Botox injections actually improve voice quality and function. The AdSD subjects rated a significantly improved voice quality and function after Botox treatment. However, the results were never within normal limits. Perceptually, the characteristic and severely impaired AdSD voice improved, but another "type" of pathological voice was detected after Botox treatment. Acoustic analyses demonstrated a significant improvement, as well. Nevertheless, the "optimally" treated AdSD voice still remained significantly deviant as compared to normal voice production. Currently, Botox injection is the therapy of first choice for AdSD. Although significant improvement could be measured in our study perceptually, acoustically, and subjectively, the optimal voice that was achieved never fully matched normal voice quality or function.

An improved system approach towards future cochlear implants.

Cochlear implants (CIs) have been used for many years to restore hearing for deaf patients. Unfortunately, today's CIs are still bulky devices and uncomfortable to wear. In this paper we present three innovations that ultimately should pave the way to a fully implantable bionic ear. First a microfabrication process used to fabricate the polymer metal microelectrode array for auditory nerve stimulation is discussed. Subsequently, a compact biphasic programmable stimulator chip to be used along with this electrode array is presented. By using a double loop feedback circuit topology, the circuit provides a precise stimulation current while requiring only little voltage headroom. The resulting low power consumption and reduced chip area allow for integration of the electronic circuitry onto the electrode array. Finally, as reliability and data transmission rate are two of the most critical issues in CI devices, we propose a software method to improve both data rate and reliability of transmitting digital data from the external part of the CI to the internal part with negligible power consumption.

Stimulus level effects on neural excitation and eCAP amplitude.

The common assumption that the electrically evoked compound action potential (eCAP) has a linear relationship with the number of excited nerve fibres is derived from the acoustical unitary response concept. This study tests the validity of this hypothesis for electrical stimulation. Five guinea pigs were implanted with the tip of a human HiFocus electrode. eCAPs were measured with the forward masking paradigm, using anodic- and cathodic-leading biphasic current pulses and the inter-pulse interval was varied. Masker and probe amplitudes were varied either individually or simultaneously. Surprisingly, at high levels decreasing eCAP amplitudes were measured with increasing stimulus current. In search for an explanation, the experimental conditions were implemented in our 3D computational model of the implanted guinea pig cochlea to perform a functional comparison. In the final experiment, with fixed inter-pulse interval (IPI) and anodic-leading pulses, increasing stimulus currents showed growing numbers of excited nerve fibres and decreasing eCAP amplitudes at high levels, again. While simulating the relative contribution of single fibres to the overall eCAP, an explanation for this could be found in a waveform change in the modelled single fibre action potentials at high levels. We conclude that highly stimulated nerve fibres have another contribution to the eCAP response than lower stimulated fibres, which leads to a reduction of the eCAP amplitude at high levels.

Clinical evaluation of the Clarion CII HiFocus 1 with and without positioner.

OBJECTIVE: To study the clinical outcomes concerning speech perception of the Clarion CII HiFocus 1 with and without a positioner and link those outcomes with the functional implications of perimodiolar electrode designs, focusing on intrascalar position, insertion depth, stimulation levels, and intracochlear conductivity pathways. DESIGN: The speech perception scores of 25 consecutive patients with the Clarion CII HiFocus 1 implanted with a positioner and 20 patients without a positioner were prospectively determined. Improved multislice CT imaging was used to study the position of the individual electrode contacts relative to the modiolus and their insertion depth. Furthermore, stimulation thresholds, maximum comfort levels, and dynamic ranges were obtained. Finally, these data were associated with intracochlear conductivity paths as calculated from the potential distribution acquired with electrical field imaging. RESULTS: Implantation with a Clarion Hifocus 1 with positioner showed significantly higher speech perception levels at 3 mos, 6 mos, and 1 yr (p < 0.05) after implantation. Basally, the positioner brought the electrode contacts significantly closer to the modiolus, whereas apically no difference in distance toward the modiolus was present. Moreover, the patients with the electrode array in a perimodiolar position showed deeper insertions. The T-levels and dynamic range were not significantly different between the positioner and nonpositioner patients. Furthermore, the intracochlear conductivity paths showed no significant differences. However, a basal current drain is present for the shallowly inserted nonpositioner patients. CONCLUSIONS: A basally perimodiolar electrode design benefits speech perception. The combination of decreased distance to the modiolus, improved insertion depth, and insulating properties of the electrode array have functional implications for the clinical outcomes of the perimodiolar electrode design. Further research is needed to elucidate their individual contributions to those outcomes.

Prediction of survival in patients with head and neck cancer.

BACKGROUND: In patients with head and neck squamous cell carcinoma (HNSCC) the estimated prognosis is usually based on the TNM classification. The relative weight of the three contributing parameters is often not completely clear. Moreover, the impact of other important clinical variables such as age, gender, prior malignancies, etc is very difficult to substantiate in daily clinical practice. The Cox-regression model allows us to estimate the effect of different variables simultaneously. The purpose of this study was to design a model for application in new HNSCC patients. In our historical data-base of patients with HNSCC, patient, treatment, and follow-up data are stored by trained oncological data managers. With these hospital-based data, we developed a statistical model for risk assessment and prediction of overall survival. This model serves in clinical decision making and appropriate counseling of patients with HNSCC. PATIENTS AND METHODS: All patients with HNSCC of the oral cavity, the pharynx, and the larynx diagnosed in our hospital between 1981 and 1998 were included. In these 1396 patients, the prognostic value of site of the primary tumor, age at diagnosis, gender, T-, N-, and M-stage, and prior malignancies were studied univariately by Kaplan-Meier curves and the log-rank test. The Cox-regression model was used to investigate the effect of these variables simultaneously on overall survival and to develop a prediction model for individual patients. RESULTS: In the univariate analyses, all variables except gender contributed significantly to overall survival. Their contribution remained significant in the multivariate Cox model. Based on the relative risks and the baseline survival curve, the expected survival for a new HNSCC patient can be calculated. CONCLUSIONS: It is possible to predict survival probabilities in a new patient with HNSCC based on historical results from a data-set analyzed with the Cox-regression model. The model is supplied with hospital-based data. Our model can be extended by other prognostic factors such as co-morbidity, histological data, molecular biology markers, etc. The results of the Cox-regression may be used in patient counseling, clinical decision making, and quality maintenance.