Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: Intraoperative results on feasibility and safety.

Human stapedius muscle (SM) can be directly and safely accessed via retrofacial approach, opening new approaches to directly measure the electrically evoked stapedius reflex threshold (eSRT). The measurement of the SM activity via direct surgical access represents a potential tool for objective eSRT fitting of cochlear implants (CI), increasing the benefit experienced by the CI users and leading to new perspectives in the development of smart implantable neurostimulators. 3D middle-ear reconstructions created after manual segmentation and related SM accessibility metrics were evaluated before the CI surgery for 16 candidates with assessed stapedius reflex. Retrofacial approach to access the SM was performed after facial recess exposure. In cases of poor exposition of SM, the access was performed anteriorly to the FN via drilling of the pyramidal eminence (PE). The total access rate of the SM via both the retrofacial and anterior approach of the FN was 100%. In 81.2% of cases (13/16), the retrofacial approach allowed to access the SM on previously categorized well exposed (8/8), partially exposed (4/5), and wholly concealed (1/3) SM with respect to FN. Following intraoperative evaluation in the remaining 18.8% (3/16), the SM was accessed anteriorly via drilling of the PE. Exposure of SM with respect to the FN and the sigmoid sinus's prominence was a predictor for the suitable surgical approach. The retrofacial approach offers feasible and reproducible access to the SM belly, opening direct access to electromyographic sensing of the eSRT. Surgical planner tools can quantitatively assist pre-surgical assessment.

The Relationship between Electrical Stapedius Reflex Thresholds and Behaviorally Most Comfortable Levels in Experienced Cochlear Implant Users.

OBJECTIVES: Programming the cochlear implant's speech processor with subjective methods in young, uncooperative children is difficult. Since young children cannot provide adequate feedback to the clinician, objective methods which do not require patient's response were often used. Electrical Stapedius Reflex Test is one of the most common procedures used. The goal of this study was to investigate the relationship between electricalstapedius reflex thresholds and behaviorally most comfortable levels in experienced cochlear implant users. MATERIALS AND METHODS: The patients implanted with two brands of cochlear implants were compared in terms of electrical stapedius reflex thresholds versus most comfortable levels. Speech tests results were also compared between the two groups. 46 cochlear implanted patients who had at least 1 year of cochlear implant experience were included in the study. 28 patients were implanted with Nucleus, 18 patients with Med-El devices. RESULTS: Moderate correlations were obtained between Electrical Stapedius Reflex (ESR) thresholds and C levels in Nucleus users; higher correlations were obtained for Med-El patients. ESR thresholds were present at higher levels than MCL/C levels in both Nucleus and Med-El users. No significant difference was obtained between the two groups in terms of speech tests. CONCLUSION: ESR test can be very informative for programming young and uncooperative patients.

Multi-electrode sequential versus single electrode stimulation to elicit the stapedial reflex during cochlear implantation: Correlation with maximum comfort level.

OBJECTIVES: To assess whether electrical stimulation sequentially delivered through 4 electrodes located in different cochlear areas may elicit the stapedial reflex at lower levels compared to single electrode stimulation and to correlate the sequentially obtained values with the maximum comfort level (C-level). PATIENTS AND METHODS: A retrospective study was performed on 35 post-verbal adult patients (age 19-80 years) consecutively implanted in 2 cochlear implant centers, evaluating the level of stimulation (pulse width) necessary to electrically evoke the stapedial reflex with two different stimulation modalities: single electrode versus sequential 4 electrode stimulation. Threshold values were compared with C-level obtained at activation. RESULTS: The average differences of pulse width and C-level were significantly smaller (P<0.0001) when the stapedial reflex was obtained with the sequential stimulation modality and reached statistical significance for every single electrode (P<0.0001). CONCLUSIONS: Stapedial reflex thresholds obtained with sequential stimulation through 4 different electrodes significantly correlate to the C-level obtained at the first setting and may be helpful in defining the upper limit of the dynamic field during initial CI mapping.

The Value of Electrically Evoked Stapedius Reflex in Determining the Maximum Comfort Level of a Cochlear Implant.

BACKGROUND: One of the most important steps for good user performance with a cochlear implant (CI) is activation and programming, aimed at determining the dynamic range. In adults, current levels are determined by psychophysical measures. In babies, small children, or individuals with multiple disorders, this procedure requires techniques that may provide inconsistent responses because of auditory inexperience or the age of the child, making it a very difficult process that demands the collaboration of both the patient and the family. PURPOSE: To study the relationship between the electrically evoked stapedius reflex threshold (ESRT) and maximum comfort level for stimulating electrodes (C-level) in postoperative CI users. RESEARCH DESIGN: Cross-sectional analytical observational case series study. STUDY SAMPLE: We assessed 24 patients of both sexes, aged between 18 and 68 yr, submitted to CI surgery. INTERVENTION: Otoscopy and immittance. Next, an implant speech processor connected to an Itautec® computer containing the manufacturer's software (custom sound Ep 3-2) was used, as well as an AT 235h probe inserted into the ear contralateral to the CI to capture the stapedius reflex, obtaining electrically evoked stapedius reflex thresholds. DATA COLLECTION AND ANALYSIS: Data from the last programming, defining C-levels for each electrode studied, were extracted from the databank of each patient. The manual decay function of the AT 235h middle ear analyzer was used to observe ESRT response in a same window for a longer response capture time. Electrodes 22, 16, 11, 6, and 1 were tested when active, with the aim of using electrodes over the entire length of the CI, and ESRT was considered present when compliance was ≥0.05 ml. Stimuli, in current units, were always initiated at 20 cu above the C-level. The analysis of variance parametric test, Tukey's honest significant difference test, the t-test, Wilcoxon nonparametric test, and the Kolmogorov-Smirnov test examined whether significant relationships existed between these other factors. RESULTS: The results demonstrate that all the electrodes selected for the study exhibited higher mean reflex threshold values than their mean C-level counterparts. However, there was no significant difference between them, for electrodes 1, 6, 11, and 16. The data provided allow the use of ESRT to define C-level values and make it possible to stipulate a correction factor ranging between 6 and 25.6 electrical units. CONCLUSION: The use of electrically evoked stapedius reflex thresholds can help the team in charge of programming CIs, making the process faster and safer, mainly for infants, small children, or individuals with multiple disorders.

Measurement of the Electrically Evoked Stapedial Reflex Response with Wideband Acoustic Reflectance Measurement.

BACKGROUND: The electrically evoked stapedial reflex threshold (ESRT) has been shown to be a good predictor of upper stimulation level for cochlear implant recipients. Previous research has shown that the ESRT may be recorded at lower stimulation levels and with a higher incidence of success with the use of higher frequency probe tones (e.g., 678 and 1000 Hz) relative to the use of the conventional 226-Hz probe tone. Research has also shown that the acoustic reflex may be recorded at lower stimulus levels with the use of wideband reflectance when compared to the acoustic reflex threshold recorded with a conventional acoustic immittance measurement. PURPOSE: The objective of this study was to compare the ESRT recorded with acoustic immittance and wideband reflectance measurements. RESEARCH DESIGN: A repeated measures design was used to evaluate potential differences in ESRTs with stimulation at an apical, middle, and basal electrode contact with the use of two different techniques, acoustic immittance measurement and wideband reflectance. STUDY SAMPLE: Twelve users of Cochlear Nucleus cochlear implants were included in the study. DATA COLLECTION AND ANALYSIS: Participants' ESRTs were evaluated in response to simulation at three different electrode contact sites (i.e., an apical, middle, and basal electrode contact) with the use of two different middle ear measurement techniques, acoustic immittance with the use of a 226-Hz probe tone and wideband reflectance with the use of a chirp stimulus. RESULTS: The mean ESRT recorded with wideband reflectance measurement was significantly lower when compared to the ESRT recorded with acoustic immittance. For one participant, the ESRT was not recorded with acoustic immittance before reaching the participant's loudness discomfort threshold, but it was successfully recorded with the use of wideband reflectance. CONCLUSIONS: The ESRT may potentially be recorded at lower presentation levels with the use of wideband reflectance measures relative to the use of acoustic immittance with a 226-Hz probe tone. This may allow for the ESRT to be obtained at levels that are more comfortable for the cochlear implant recipient, which may also allow for a higher incidence in the successful recording of the ESRT.

An Objective Method to Determine the Electrically Evoked Stapedius Reflex Threshold During Cochlea Implantation.

OBJECTIVE: In cochlea implantation, assessment of the electrically evoked stapedius reflex threshold (eSRT) provides information for postoperative adjustment of the speech processor. This is used to prevent undesired overstimulation. To this day, the reflex is visually identified by the surgeon. However, this method may be prone to error due to ventilation-associated situs excursions, blinking, or other distractions. Therefore, the aim of this study was to establish an objective and automatized method to determine the eSRT. METHODS: Video material documenting the intraoperative measurements was analyzed offline applying a tracking software to quantify stapes head movements. Moreover, a computer program (TrackerAnalyzer) was developed to detect reflex associated movements automatically. RESULTS: Reflex responses seen visually by the surgeon compared with visual registration on the video material postoperatively and to results of the automatized method with TrackerAnalyzer showed a high inter-rater agreement (Cohen's kappa coefficient = 0.47-0.59). 82% of events in which the TrackerAnalyzer registered reflexes that were not seen by the surgeon had values close but lower to the intraoperatively determined eSRT (mean -1.02 current units). CONCLUSION: We demonstrated the feasibility of an objective and automatized method to determine electrically evoked stapedius reflex thresholds in cochlea implantation.

Normative Wideband Reflectance, Equivalent Admittance at the Tympanic Membrane, and Acoustic Stapedius Reflex Threshold in Adults.

OBJECTIVES: Wideband acoustic immittance (WAI) measures such as pressure reflectance, parameterized by absorbance and group delay, equivalent admittance at the tympanic membrane (TM), and acoustic stapedius reflex threshold (ASRT) describe middle ear function across a wide frequency range, compared with traditional tests employing a single frequency. The objective of this study was to obtain normative data using these tests for a group of normal-hearing adults and investigate test-retest reliability using a longitudinal design. DESIGN: A longitudinal prospective design was used to obtain normative test and retest data on clinical and WAI measures. Subjects were 13 males and 20 females (mean age = 26 years). Inclusion criteria included normal audiometry and clinical immittance. Subjects were tested on two separate visits approximately 1 month apart. Reflectance and equivalent admittance at the TM were measured from 0.25 to 8.0 kHz under three conditions: at ambient pressure in the ear canal and with pressure sweeps from positive to negative pressure (downswept) and negative to positive pressure (upswept). Equivalent admittance at the TM was calculated using admittance measurements at the probe tip that were adjusted using a model of sound transmission in the ear canal and acoustic estimates of ear-canal area and length. Wideband ASRTs were measured at tympanometric peak pressure (TPP) derived from the average TPP of downswept and upswept tympanograms. Descriptive statistics were obtained for all WAI responses, and wideband and clinical ASRTs were compared. RESULTS: Mean absorbance at ambient pressure and TPP demonstrated a broad band-pass pattern typical of previous studies. Test-retest differences were lower for absorbance at TPP for the downswept method compared with ambient pressure at frequencies between 1.0 and 1.26 kHz. Mean tympanometric peak-to-tail differences for absorbance were greatest around 1.0 to 2.0 kHz and similar for positive and negative tails. Mean group delay at ambient pressure and at TPP were greatest between 0.32 and 0.6 kHz at 200 to 300 µsec, reduced at frequencies between 0.8 and 1.5 kHz, and increased above 1.5 kHz to around 150 µsec. Mean equivalent admittance at the TM had a lower level for the ambient method than at TPP for both sweep directions below 1.2 kHz, but the difference between methods was only statistically significant for the comparison between the ambient method and TPP for the upswept tympanogram. Mean equivalent admittance phase was positive at all frequencies. Test-retest reliability of the equivalent admittance level ranged from 1 to 3 dB at frequencies below 1.0 kHz, but increased to 8 to 9 dB at higher frequencies. The mean wideband ASRT for an ipsilateral broadband noise activator was 12 dB lower than the clinical ASRT, but had poorer reliability. CONCLUSIONS: Normative data for the WAI test battery revealed minor differences for results at ambient pressure compared with tympanometric methods at TPP for reflectance, group delay, and equivalent admittance level at the TM for subjects with middle ear pressure within ±100 daPa. Test-retest reliability was better for absorbance at TPP for the downswept tympanogram compared with ambient pressure at frequencies around 1.0 kHz. Large peak-to-tail differences in absorbance combined with good reliability at frequencies between about 0.7 and 3.0 kHz suggest that this may be a sensitive frequency range for interpreting absorbance at TPP. The mean wideband ipsilateral ASRT was lower than the clinical ASRT, consistent with previous studies. Results are promising for the use of a wideband test battery to evaluate middle ear function.

Assessment of the Brainstem-Mediated Stapedius Muscle Reflex in Andean Children Living at High Altitudes.

Counter, S. Allen, Leo H. Buchanan, Fernando Ortega, Anthony B. Jacobs, and Göran Laurell. Assessment of the brainstem-mediated stapedius muscle reflex in Andean children living at high altitudes. High Alt Med Biol. 18:37-45, 2017.-This study examined the physiological thresholds, amplitude growth, and contraction duration of the acoustic stapedius reflex (ASR) in Andean children aged 2-17 years living at altitudes of 2850 m (Altitude I Group) and 3973 m (Altitude II Group) as part of a general medical assessment of the health status of the children. The brainstem-mediated ASR reveals the integrity of the neuronal components of the auditory reflex arc, including the cochlea receptors, eight cranial nerves, and brainstem neural projections to the cochlear nuclei, bilateral superior olivary nuclei, facial nerve nuclei, and facial nerve and its stapedius branch. Uncrossed (ipsilateral) and crossed (contralateral) ASR thresholds (ASRT), ASR amplitude growth (ASRG) function, and ASR muscle contraction duration (decay/fatigue) (ASRD) were measured noninvasively with 500, 1000 Hz and broadband (bandwidth = 125-4000 Hz) noise stimulus activators using a middle ear immittance system. Oxygen saturation (SaO2) level and heart rate were measured in a subsample of the study group. Statistical analyses revealed that the Altitude I and Altitude II groups had ASRT, ASRG function, and ASRD rates comparable to children at sea level and that the two groups were not significantly different for any of the ASR measures. No significant association was found between SaO2 or heart rate and ASRT, growth, and muscle fatigue rate. In conclusion, the assessment of the ASR in children in the high-altitude groups revealed normal function. Furthermore, the results indicate no adverse oto-physiological effects of altitude on the brainstem-mediated ASR at elevations between 2850 and 4000 m and suggest normal middle ear and auditory brainstem function.

On the origin of ear clicks during deglutition or pressure equalization.

To explore the origin of clicking sounds in the ear during deglutition or other pharyngeal movements, which are interpreted differently in the literature. Experimental study at a tertiary referral centre. Acoustic phenomena during a forced opening test of the Eustachian tube (ET) were studied in a temporal bone model. Additionally, in vivo experiments were carried out in healthy volunteers for ruling out movements of the ossicular chain or the drumhead as potential causes of clicks. Thus, acoustic recordings were performed parallel to stapedius or tensor reflex measurements or pneumatic video endoscopies of the tympanic membrane. Obviously the acoustic signals (clicks) appear when the tube opens, which could be visualized and acoustically recorded during forced opening tests in temporal bone experiments. Middle ear muscle contractions with movements of the tympanic membrane did not cause any click events. Together with the results of a previous paper (9) we interpret the clicks as disruptions of fluid or mucus films covering the mucosa during the ET opening. The final goal of our studies is to use such clicks as indicators of ET openings in a new tube function test, which has to be elaborated.

Comparison of eSRTs and comfort levels in users of Digisonic SP cochlear implants.

OBJECTIVE: This project proposes to assess the relation between the electrical stapedius reflex threshold (eSRT) and comfort levels in users of the Digisonic SP cochlear implant. METHODS: Cross-sectional study, where eSRTs are compared to the comfort current levels at 2 weeks and at 1-year post-fitting in a group of 11 adults getting a significant improvement in open set speech recognition from a Digisonic SP cochlear implant. RESULTS: The linear relation between eSRTs and comfort levels results in Pearson correlation coefficients of 0.65 (P < 0.01; at 2 weeks) to 0.60 (P < 0.05; at 1 year). The comfort levels can be predicted from the eSRTs for the Digisonic SP device from the model equation C level = 19.12 + 0.41*eSRT within a clinically acceptable margin of error. DISCUSSION: Reflex thresholds could be obtained in most participants, and in most channels of the Digisonic implant. The equation model appears as a quite reliable predictor of comfort levels for users of this device.

Voluntary eardrum movement: a marker for tensor tympani contraction?

HYPOTHESIS: Voluntary eardrum movement (VEM) and resultant tympanometric changes reflect tensor tympani (TT) contraction. BACKGROUND: TT contraction has been hypothesized to cause symptoms of aural fullness, tinnitus, clicking, and even vertigo despite the lack of understanding of how it functions or what causes it to contract. Identifying tympanometric changes unique to TT contraction can provide a diagnostic tool for identifying its role in pathologic conditions. METHODS: Various tympanometric measurements were performed on human subjects who could voluntarily move their eardrums. These were compared with similar tympanometric measurements performed on cadaveric temporal bones while manually tensing the TT and stapedius muscles individually. RESULTS: Eight subjects (14 ears) who could cause VEM were identified. Compared with baseline, VEM resulted in significantly decreased middle ear compliance (p < 0.01) and middle ear pressure (p < 0.01) measurements. The compliance changes seen with VEM were larger than those seen with acoustically stimulated stapedius contraction. Finally, the direction of compliance change with VEM was dependent on the pressure applied to the external auditory canal (EAC), with compliance increasing with positive EAC pressure. This was not seen with stapedius contraction. These findings were reproduced using the cadaveric temporal bone model: larger compliance changes with pull on TT as compared with stapedius with neutral EAC probe pressure; change in direction of compliance changes with varying EAC probe pressure with TT pull, not with stapedius pull. CONCLUSION: TT contraction produces distinctive tympanometric findings that can be used to support its abnormal contraction in ears with symptoms compatible with TT syndrome.

The relationship between electrical auditory brainstem responses and perceptual thresholds in Digisonic® SP cochlear implant users.

Determining the electrical stimulation levels is often a difficult and time-consuming task because they are normally determined behaviorally - a particular challenge when dealing with pediatric patients. The evoked stapedius reflex threshold and the evoked compound action potential have already been shown to provide reasonable estimates of the C- and T-levels, although these estimates tend to overestimate the C- and T-levels. The aim of this study was to investigate whether the evoked auditory brainstem response (eABR) can also be used to reliably estimate a patient's C- and T-levels. The correlation between eABR detection thresholds and behaviorally measured perceptual thresholds was statistically significant (r = 0.71; P < 0.001). In addition, eABR Wave-V amplitude increased with increasing stimulation level for the three loudness levels tested. These results show that the eABR detection threshold can be used to estimate a patient's T-levels. In addition, Wave-V amplitude could provide a method for estimating C-levels in the future. The eABR objective measure may provide a useful cochlear implant fitting method - particularly for pediatric patients.

Vocalization-induced stapedius contraction.

OBJECTIVE: To present a case of a patient with visible stapedius contraction on vocalization and to discuss the related literature. PATIENTS: A 51 year-old woman with a Type III myringostapediopexy due to chronic suppurative otitis media and an incidental finding of voice-induced movement of the stapes head. INTERVENTIONS: Otoendoscopy, pure tone and impedance audiometry, and modified stapedius reflex decay. MAIN OUTCOME MEASURE: Stapes head movement on otoendoscopy. RESULTS: Stapes head movement was seen endoscopically on vocalization but not on tympanometric measures. CONCLUSION: Visible stapedius contraction with vocalization is an uncommon phenomenon. Our understanding of the nonauditory pathways to stapedius is limited and requires further research.

Increased contralateral suppression of otoacoustic emissions indicates a hyperresponsive medial olivocochlear system in humans with tinnitus and hyperacusis.

Atypical medial olivocochlear (MOC) feedback from brain stem to cochlea has been proposed to play a role in tinnitus, but even well-constructed tests of this idea have yielded inconsistent results. In the present study, it was hypothesized that low sound tolerance (mild to moderate hyperacusis), which can accompany tinnitus or occur on its own, might contribute to the inconsistency. Sound-level tolerance (SLT) was assessed in subjects (all men) with clinically normal or near-normal thresholds to form threshold-, age-, and sex-matched groups: 1) no tinnitus/high SLT, 2) no tinnitus/low SLT, 3) tinnitus/high SLT, and 4) tinnitus/low SLT. MOC function was measured from the ear canal as the change in magnitude of distortion-product otoacoustic emissions (DPOAE) elicited by broadband noise presented to the contralateral ear. The noise reduced DPOAE magnitude in all groups ("contralateral suppression"), but significantly more reduction occurred in groups with tinnitus and/or low SLT, indicating hyperresponsiveness of the MOC system compared with the group with no tinnitus/high SLT. The results suggest hyperresponsiveness of the interneurons of the MOC system residing in the cochlear nucleus and/or MOC neurons themselves. The present data, combined with previous human and animal data, indicate that neural pathways involving every major division of the cochlear nucleus manifest hyperactivity and/or hyperresponsiveness in tinnitus and/or low SLT. The overactivation may develop in each pathway separately. However, a more parsimonious hypothesis is that top-down neuromodulation is the driving force behind ubiquitous overactivation of the auditory brain stem and may correspond to attentional spotlighting on the auditory domain in tinnitus and hyperacusis.

[The clinical application of objective hearing monitoring technology in cochlear implants].

OBJECTIVE: Compare the clinical characteristics and application value between elcetrically evoked stapedius responses and neural response telemetry. METHOD: Select number 1, 7, 11, 17, 22 electrodes from 21 cochlear implanting nucleus 24R cochlear implants, using NRT3.0 software provided by Cochlear corporation to test the threshold of elcetrically evoked stapedius responses and neural response telemetry during operation and subjective psychological physical test after operation repectively named elcetrically evoked stapedius responses threshold, electrically evokded compound aciton potentials threshold, and T-levels. Respectively study the correlations of ESRT, ECAP threshold, and T-levels. RESULT: The detection rates of ESRT, NRT, and T-levels were 96.19%, 93.33%, 100%. The mean thresholds of ESRT were 206.61 +/- 10. 74, 208.48 +/- 13.64, 205.52 +/- 14. 63, 203.76 +/- 12.97, 199.50 +/- 11.19; The mean thresholds of NRT were 184.11 +/- 6.35, 188.55 +/- 11.70, 187.00 +/- 12.29, 181.85 +/- 13.22, 179.00 +/- 10.50; The mean thresholds of T levels were 145.48 +/- 18.66, 148.62 +/- 8.22, 146.62 +/- 18.08, 142.52 +/- 13.11, 140.33 +/- 13.68. The mean thresholds of ESRT in each electrode were rather greater than that of T-levels. There is a high degree of consistency in the mean thresholds of ES RT, NRT and T-levels. The test time, test means, unilaterally detection rate during operation, ESR is better than NRT. All the electrodes were set as observation objects, the correlation of ESRT and NRT is 0.69, the correlation of NRT and T is 0.62, and the correlation of ESRT and T is 0.39. CONCLUSION: The application of elcetrically evoked stapedius responses and neural response telemetry during operation can rapidly estimate wether the implant is in good condition and the pathway is normal. Rather than neural response telemetry, elcetrically evoked stapedi us responses is more flexible, convienient, accurate and visual, while it is more objective superiority after operation especially for young children for the former detector.

Unilateral cochlear implant use promotes normal-like loudness perception in adolescents with childhood deafness.

OBJECTIVES: Behavioral measures of cochlear implant (CI) device stimulation levels can be difficult to obtain in individuals with limited or no hearing experience. Loudness measures are particularly challenging. It would therefore be useful to have a battery of objective and behavioral measures to determine CI stimulation levels in listeners with childhood deafness. In the present study, the authors characterized loudness growth in 20 adolescents: 8 with normal hearing and 12 CI participants with pre/perilingual bilateral sensorineural hearing loss. They asked (1) do adolescent CI users with childhood deafness experience similar increases in loudness as their peers with normal hearing? and (2) can loudness be predicted by objective measures of auditory activity? The authors hypothesized that loudness perception would be significantly different between CI and normal-hearing groups and that it would correlate with objective measures. DESIGN: CI users were recruited from the Cochlear Implant Program at The Hospital for Sick Children and all had used unilateral Nucleus CIs for at least 2 years. The dynamic range for each participant was defined as the difference between the behavioral threshold and the electrically evoked stapedius reflex (ESR) threshold. Loudness growth was assessed within this range behaviorally on a continuous visual scale and objectively with physiological measures. Auditory brainstem responses (ABRs) and ESRs were recorded in both groups and electrically evoked compound action potentials (ECAPs) of the auditory nerve were recorded in addition in CI listeners. The regression line slopes of ECAP and ABR amplitude growth functions were then calculated and compared with behavioral loudness growth slopes in the upper portion (40-100%) and lower portion (0-40%) of the dynamic range. Electrical pulse stimuli (in CI users) and acoustic clicks (in normal-hearing participants) were presented within each participant's dynamic range. RESULTS: The mean dynamic range in CI listeners was more variable than in normal-hearing individuals. Despite this difference, loudness at the ESR threshold was not significantly different in CI adolescents from their normal-hearing peers, and CI users exhibited normal-like loudness growth. There was a significantly positive correlation between ECAP amplitude growth and loudness growth in CI users in the upper portion of the dynamic range, while ABR wave V amplitude growth was not related to loudness growth in either group. CONCLUSIONS: We confirmed that the ESR threshold is a good measure of comfortably loud levels in adolescents with cochlear implants and their normal-hearing peers. Adolescents using CIs show normal-like rates of loudness growth on average, despite having highly variable dynamic ranges of hearing. Individual rates of loudness growth in the upper dynamic range in CI users can be predicted by the rate of amplitude growth of the ECAP. Thus, the rate of neural recruitment with increasing CI current is important for loudness perception in pre/perilingually deaf listeners and should be considered when programming their CIs.

Would an endosteal CI-electrode make sense? Comparison of the auditory nerve excitability from different stimulation sites using ESRT measurements and mathematical models.

UNLABELLED: Regarding potential endosteal cochlear implant electrodes, the primary goal of this paper is to compare different intra- and extra-cochlear stimulation sites in terms of current strengths needed for stimulating the auditory nerve. Our study was performed during routine cochlear implantation using needle electrodes for electric stimulation and by visually recording electrically elicited stapedius reflexes (ESRT) as a measure for the stimulus transfer. Of course this rather simple setup only allows rough estimations, which, however, may provide further arguments whether or not to proceed with the concept of an endosteal electrode. In addition, a mathematical model is being developed. In a pilot study, intra-operative electric stimuli were applied via a needle electrode commonly used for the promontory stimulation test. Thus, stapedius reflex thresholds (ESRTs), electrically elicited via the needle from different points inside and outside the cochlea served as indicators for the suitability of different electrode positions towards the modiolus. Tests were performed on 11 CI-recipients. In addition, the extension of electrical fields from different stimulation sites is simulated in a mathematical cochlea model. In most patients ESRT measurements could be performed and evaluated. Thus an "endosteal" stimulation seems possible, although the current intensities must be higher than at intraluminal stimulation sites. Moreover, our model calculations confirm that the extension of electric fields is less favourable with increasing distance from the electrode to the ganglion nerve cells. In terms of hearing, the concept of an endosteal electrode should only be promoted, if its superiority for hearing preservation can be proven, e.g. in animal experiments. However, for other indications like the electric suppression of tinnitus, further research seems advisable. LEVELS OF EVIDENCE: N/A.

[The objective method for recording stapedial reflex during surgery for cochlear implantation].

The purpose of the present study was to develop a method for the objective registration of the stapedial reflex at the contralateral ear during cochlear implantation surgery on the affected one. The excessive pressure in the middle ear (up to 500 daPa) was compensated by the administration of an additional air volume (1 liter) into the AA220 impedance meter pneumatic circuit. A syringe was used to measure variations of pressure in the new pneumatic circuit. Eight of the 12 patients demonstrated coincident visual and objective reflex thresholds. In the remaining 4 patients, the visually apparent stapedial reflex thresholds proved higher than those obtained objectively by the standard procedure of impedancemetry. It is concluded that the objective registration of the stapedial reflex excludes the effect of subjective factors interfering with its estimation and provides the possibility for comparative intra- and postoperative studies using one and the same instrument.

No evidence for peripheral mechanism attenuating auditory ERPs to self-induced tones.

The N1 and P2 event-related potentials (ERPs) are attenuated when the eliciting sounds coincide with our own actions. Although this ERP attenuation could be caused by central processes, it may also reflect a peripheral mechanism: the coactivation of the stapedius muscle with the task-relevant effector, which reduces signal transmission efficiency in the middle ear, reducing the effective intensity of concurrently presented tones, which, in turn, elicit lower amplitude auditory ERPs. Because stapedius muscle contraction attenuates frequencies below 2 kHz, no attenuation should occur at frequencies above 2 kHz. A self-induced tone paradigm was administered with 0.5, 2.0, and 8.0 kHz pure tones. Self-induced tones elicited attenuated N1 and P2 ERPs, but the magnitude of attenuation was not affected by tone frequency. This result does not support the hypothesis that ERP attenuation to self-induced tones are caused by stapedius muscle contractions.

Acoustic stapedius reflex function in man revisited.

OBJECTIVE: The objective of this study was to examine the role of the acoustic stapedius reflex in the protection of speech recognition from the upward spread of masking arising from low-frequency background noise. DESIGN: Speech recognition scores were measured for nine control participants (19-34 years) and six patients with transected stapedius tendons poststapedotomy (39-57 years) as a function of the amplitude of a low-frequency masker, presented at nominal signal to noise ratios of +5 dB, -5 dB, and -15 dB. All participants had pure-tone hearing thresholds in the normal range. Continuous high-pass noise was present in all conditions to avoid ceiling effects; this reduced performance in quiet to approximately 85% for all participants. Scores were measured for soft and loud nonsense syllables (average third octave band levels of 35 and 65 dB SPL), so that a comparison of the low-frequency noise masking functions at the two levels would provide information about the effects of the reflex on speech intelligibility in noise. A third group of nine control participants (19-22 years) listened in the presence of a low-frequency masker gated to come on 1 sec before stimulus onset, to reduce the likelihood of reflex adaptation. The Speech-Intelligibility Index was used to quantify the amount of speech information available in each condition. RESULTS: Patients with transected tendons performed more poorly than control participants as a function of Speech-Intelligibility Index in all conditions, even at levels that were too soft for reflex activation. This could be because of postsurgical differences in sensitivity, the more advanced age of poststapedotomy group, or differences in medial olivocochlear inhibition. For loud speech, patient performance fell nearly linearly with increases in the low-frequency masker, but control participants' performance declined little as the signal to noise ratio declined from +5 to -5 dB, and then fell rapidly as the ratio declined to -15 dB. This plateau in the masking function did not occur for the patients. Masking functions obtained with the gated low-frequency masker were either highly similar or poorer to those obtained with a continuous masker, suggesting that the use of a continuous low frequency masker did not result in significant reflex adaptation. CONCLUSIONS: The stapedius reflex appears to offer some protection from the upward spread of masking of speech by background low-frequency noise at moderate levels, but not at high levels.