Ekkehard Stürzebecher

Combined Electric and Acoustic Stimulation of the Auditory System: Results of a Clinical Study

Combined electric and acoustic stimulation (EAS) of the auditory system is a new therapy for patients with severe to profound high- and mid-frequency hearing loss but remaining low-frequency hearing. In a prospective study, 13 patients with low-frequency hearing of better than 60 dB below 1 kHz were implanted with a MED-EL COMBI 40+ cochlear implant. Pure tone thresholds as well as monosyllabic word scores and Hochmair-Schulz-Moser sentences in quiet and in noise were measured with hearing aids, cochlear implant alone and in the combined stimulation mode (EAS) in the same ear. Hearing could be partially preserved in 11 out of the 13 patients. All patients scored significantly higher with cochlear implant alone than with hearing aids. Seven patients scored higher in the EAS mode than with cochlear implant alone for sentences in noise, 4 remained unchanged, and 2 could not use EAS. Synergistic effects of EAS were most prominent for hearing in noise with increases of up to 72% as compared to cochlear implant alone.

Auditory steady-state responses to chirp stimuli based on cochlear traveling wave delay.

This study investigates the use of chirp stimuli to compensate for the cochlear traveling wave delay. The temporal dispersion in the cochlea is given by the traveling time, which in this study is estimated from latency-frequency functions obtained from (1) a cochlear model, (2) tone-burst auditory brain stem response (ABR) latencies, (3) and narrow-band ABR latencies. These latency-frequency functions are assumed to reflect the group delay of a linear system that modifies the phase spectrum of the applied stimulus. On the basis of this assumption, three chirps are constructed and evaluated in 49 normal-hearing subjects. The auditory steady-state responses to these chirps and to a click stimulus are compared at two levels of stimulation (30 and 50 dB nHL) and a rate of 90s. The chirps give shorter detection time and higher signal-to-noise ratio than the click. The shorter detection time obtained by the chirps is equivalent to an increase in stimulus level of 20 dB or more. The results indicate that a chirp is a more efficient stimulus than a click for the recording of early auditory evoked responses in normal-hearing adults using transient sounds at a high rate of stimulation.

Results of Cochlear Implantation in Patients with Severe to Profound Hearing Loss—Implications for Patient Selection

In patients with some residual hearing and minor benefit from conventional hearing aids, the benefits of cochlear implantation have to be weighed carefully against eventual adverse effects. In this study, pre- and post-operative thresholds as well as functional results after cochlear implantation are reported; 17 of 44 implanted adults had residual hearing pre-operatively (mean threshold(250 to 4000 Hz): 106 dB HL) in the implanted ear. Residual hearing in the implanted ear could not, in general, be preserved post-operatively. Seventeen of 44 implanted children had some amount of residual hearing in the implanted ear pre-operatively (implanted ear: 114 dB HL; contralateral ear: 109.9 dB HL; mean thresholds(250 to 4000 Hz))). Contrary to the results in adults, residual hearing in the implanted ear remained statistically unchanged. Hearing in the contralateral ear increased significantly from 109.9 to 101.9 dB HL post-operatively. This increase was mainly attributed to maturation of the central auditory pathway. In adults with residual hearing, the monosyllable word recognition scores increased significantly from 9 per cent pre-operatively to 42 per cent post-operatively. Children with residual hearing tended to perform better on speech-related test material compared to children without prior auditory experience. Cochlear implantation is indicated in adults and children with residual hearing and minor benefit from conventional amplification. The contralateral ear in children should be considered for additional acoustical stimulation.

Objective Response Detection in the Frequency Domain: Comparison of Several q-Sample Tests

The objective assessment of the hearing threshold requires a suitable statistical test for response detection. For checking the q spectral lines of an auditory-evoked potential spectrum in the frequency domain, a q-sample test seems to be more favourable compared to q applications of a one-sample test. The response detection performance of three q-sample tests (q-sample analogue of Watsons U2 test, q-sample uniform scores test and a modified q-sample uniform scores test) has been checked by extensive Monte Carlo simulations. To compare the performance of the three test statistics, sensitivity was calculated and receiver-operating characteristics were constructed from the probability density functions estimated by the Monte Carlo simulations. In addition, a comparison on the basis of real near-threshold auditory brainstem response data was carried out. The modified q-sample uniform scores test appeared to be the most powerful test. Some aspects of the practical application of this test are discussed in this paper.

Automated auditory response detection: Statistical problems with repeated testing Evaluación repetida en la detección de respuestas auditivas

Sequential application of a statistical test is usually applied in an automated auditory response detection algorithm. The sequential test strategy is very time-efficient but increases the probability of a false rejection of the null-hypothesis. For this reason, it is necessary to correct the critical test value. However, the well-known Bonferroni correction leads to an over-correction when dealing with dependent or partly dependent data. The objective of the study reported here was to develop a method to determine the critical test value for the sequential testing of dependent data. Extensive Monte Carlo simulations were used to develop this method. The simulation results were reviewed and the benefit of the suggested method, in comparison to the Bonferroni correction, was shown using a large sample of real amplitude modulation following response data. The detection rate determined for these data and the ROC curve demonstrate the advantage of using the method suggested here.

Objective Detection of the Amplitude Modulation Following Response (AMFR):Detectión objetiva de la respuesta consecuente de amplitud modulada (AMFR)

The amplitude modulation following response (AMFR) has been shown to be a promising tool for objective frequency-specific assessment of hearing thresholds in children. AMFR is represented in the frequency domain by a single spectral line. This simplifies the objective statistical detection in comparison to other responses with a more complex waveform. The aim of the present study is to compare the performance of four known tests (phase coherence (PC), new Hotelling T2 (HT2*), modified PC (PC*), magnitude-squared coherence (MSC)) on the basis of a large sample (n = 1484) of AMFR recordings (stimulus level of 30 dB nHL in normally-hearing subjects, and 30 dB SL in hearing-impaired subjects) to find the test best suited for AMFR detection. The decision was made on the basis of the detection rates as well as of the ROC curves. Based on the large data pool, MSC and PC* show equal performance and a small but consistent advantage in objective detection of AMFR over HT2* and PC.

Click-evoked ABR at high stimulus repetition rates for neonatal hearing screening: Potenciales auditivos evocados (ABR) por clicks a tasas altas de estimulación para la identificación de problemas auditivos en neonatos

A new, fast screening algorithm based on auditory brainstem response (ABR) recorded at a high click repetition rate is proposed. Response detection is carried out in the frequency domain by a statistical test procedure which includes the fundamental frequency and the harmonics below 800 Hz. First, the method was tested in 25 young adults. ABRs were recorded in the repetition rate range 20/s to 400/s. With a mean response detection time of 31 s, a click repetition rate of 140/s was found to be the optimum rate among the adult group. The method was then tested using a group of 114 neonates in whom the repetition rate range 60/s to 200/s was examined. At the repetition rate 90/s, which was found to be the optimum rate in neonates, the mean detection time was 24.6 s. In addition to the fast ABR detection, the proposed screening algorithm also allows simultaneous hearing screening of both ears using a one-channel data recording. Se propone un algoritmo nuevo y rápido de identificación basado en las respuestas auditivas de tallo cerebral (ABR) registradas con una tasa alta de estimulación con clicks. La detección de las respuestas se lleva a cabo en el campo fre-cuencial por medio de una prueba estadistica que incluye la frecuencia fundamental y los armónicos inferiores a 800 Hz. El método fue inicialmente probado en 25 adultos jóvenes. Las ABRs se registraron con un rango de tasas de estimulación de 20/s a 400/s. Se encontró que con una tiempo promedio de detección de la respuesta de 31 s., la tasa óptima de estimulación con clicks, para el grupo de los adultos era de 140/s. Posteriormente el método fue probado en un grupo de 114 neonatos en quienes la tasa de estimulación varió de 60/s. a 200/s. El tiempo promedio de detección fue de 24.6 s., cuando se utilizó una tasa de estimulación de 90/s., considerada como la optima para neonatos. Además de la rápida detección de ABR, el algoritmo de identificación que se propone, pcrmite también la identificación auditiva simul-tánea en ambos oídos con el uso de un sistema de registro de datos de un canal.

Efficient Stimuli for Recording of the Amplitude Modulation Following Response: Estímulos eficientes para el registro de la Respuesta de Seguimiento a la Modulación de la Amplitud (AMFR)

Amplitude modulation following response (AMFR) is a promising tool for objective frequency-specific assessment of hearing thresholds in children. The stimulus generally used for AMFR recording (one amplitude-modulated carrier) activates only a small part of the basilar membrane. Therefore, the response amplitude is small. Combined frequency and amplitude modulation is not significantly more effective. A new stimulus is proposed that is composed of several carriers. All carriers are modulated with the same modulation frequency. The signal to noise ratio of the response to the multiple-carrier stimulus is significantly increased compared with the usual one-carrier stimulus. Therefore, response detection near threshold is expected to be improved. AMFR also seems to be well suited to newborn hearing screening. Simultaneous recording of six responses (three AMFRs from each ear) to 1-, 2-, and 4-kHz multiple-carrier stimuli of a 40 dB HL stimulus level is demonstrated in normally-hearing adults. Verification in babies will be necessary.

Objective detection of auditory brainstem potentials: Comparison of statistical tests in the time and frequency domains

Newborn hearing screening with auditory brainstem potentials (ABR) requires objective ABR detection by a statistical test procedure with high performance. Statistical testing can be performed in the time or frequency domain. The aim of the present study was to compare the performance of three tests in the time domain (Friedman test, variance ratio F SP, Cochrans Q-test) with that of a test in the frequency domain (modified q-sample uniform scores test) that, in a former investigation, was shown to be the best test in the frequency domain. To compare the performance of the four tests, the test power was calculated and receiver operating characteristics (ROCs) were constructed from the probability density functions estimated using Monte Carlo simulations. In addition, a comparison on the basis of real near-threshold ABR data was carried out. The modified q-sample uniform scores test appeared to be the most powerful one. Some aspects of practical application are discussed.

Objective Detection of Auditory Evoked Potentials Comparison of Several Statistical Tests in the Frequency Domain by Means of Monte Carlo Simulations

Fully objective assessment of the hearing threshold by auditory evoked potentials requires an objective detection of these responses by means of suitable statistical tests. The Rayleigh test, Watsons U2 test, Kuipers test and Hodges-Ajnes test check the phase angle distribution of a Fourier harmonics in a sample of stimulus-related EEG epochs. The modified Rayleigh test includes, in addition to the phase angles, the amplitude information in the form of ranks of the spectral amplitudes. To compare the signal detection performance of these tests, estimates of the probability density functions were calculated by means of extensive Monte Carlo simulations. From the probability density functions, the sensitivity of the tests was calculated and receiver operating characteristics (ROC) were constructed. The modified Rayleigh test appeared to be the most powerful test, followed by the Rayleigh test and Watsons U2 test. The application of Kuipers test and Hodges-Ajnes test as well is not to be recommended for AEP detection.