Channel interactions caused by spread of the intracochlear electric field and, thus, the spread of neural excitation constrain frequency selectivity and speech recognition in cochlear implant (CI) users. Studying the influence of the spread of electric field (SEF) on the spread of excitation (SOE) can help us better understand the electrical-neural interface. The primary aim of this study was to examine the influence of the SEF on the SOE. In 38 Nucleus (Cochlear Ltd. Sydney, Australia) CI recipients, we assessed the spatial SEF by measuring the voltage drop (transimpedance) and the SOE through neural responses (electrically evoked compound action potentials [eCAPs]) along the electrode array. Transimpedance was recorded using the monopolar (MP2) mode as the stimulation and recording mode. Biphasic square-wave pulses with an amplitude of 110 CL and duration of 37 µs were used for stimulation. SOE was measured at the probe active electrodes E5, E13, and E18. The stimulation amplitudes were set individually to the thresholds of the neural response telemetry (T-NRT), which were measured by the AutoNRT protocol. The transimpedance half-widths were between 0.00 electrodes and 8.55 electrodes. The SOE half-widths reached values between 0.54 electrodes and 5.70 electrodes. Considering individual transimpedance and SOE half-widths, the SEF and SOE showed a significant positive correlation only at electrode E13. Furthermore, this study shows a significant negative correlation of the SEF and SOE in consideration of mean half-widths.

Objective: The primary aim of the study was to explore whether reduced spread of electrical field is observed after partial or subtotal cochleoectomy and cochlear implantation compared with standard cochlear implantation. Secondarily, the influence on speech perception was explored comparing both groups. Study Design: Nonconcurrent cohort study. Setting: Monocentric study at a tertiary referral center. Patients: Twenty adult cochlear implant (CI) users after tumor resection with cochleoectomy of varying extent and 20 electrode-matched CI users with standard electrode insertion. Interventions: Partial and subtotal cochleoectomy for tumor removal and CI. Outcome Measures: Trans-impedance, electrically evoked compound action potentials, and word recognition were measured. Relative impedance was computed as a function of distance between the stimulation and recording electrode. Results: Trans-impedance was smaller and more homogeneous in patients with partial or subtotal cochleoectomy than in the control group. In the tumor group, the mean relative impedance decreased to 0.20 (standard deviation [SD] = 0.03) at a distance of 1 electrode and to 0.25 (SD = 0.04) in the control group. After excluding seven patients with a second tumor in the internal auditory canal or cerebellopontine angle, with transmodiolar tumors, after near total cochleoectomy, or only extended cochleostomy, word recognition was 61% (SD = 19%) at 3 months and 75% (SD = 19%) at 12 months after activation of the audio processor in the tumor group. At 12 months, it was significantly (p < 0.05) better than in the control group (3 mo: 45%, SD = 25%; 12 mo: 53%, SD = 26%). A smaller trans-impedance is associated with a better word recognition. Conclusion: We conclude that the surgical technique used for CI surgery after subtotal cochleoectomy reduces the spread of the electric field and overcomes the potential drawbacks in structure preservation associated with that technique.

Hypothesis: Audio processor magnets used in transcutaneous active hearing implants vary in retention force. We hypothesized that a range of optimal magnetic retention forces could be derived, based on objective in-situ measurements of individual retention forces. Background: The magnetic force required to retain the proper placement of transcutaneous active hearing implants varies among patients. Currently, audiologists rely on personal experience in deciding which magnet to use. Insufficient force causes frequent loss of the single-unit processors or external coils of behind-the-ear devices, and excessive force causes pain and skin irritations. Methods: We experimentally determined magnetic retention force as a function of the distance between two magnets for different processor-implant magnet combinations. In addition, we studied individual in situ retention forces in 100 patients with hearing devices. Skin status was evaluated by a physician and assessed by patient self-reporting and a questionnaire. Results: Force–distance functions showed that different magnet strengths had differential effects only at distances less than 6 mm. Examiner and patient skin status assessments and comfort scores showed that optimal retention force range was 0.23 to 0.4 N. Conclusion: We found that the currently available magnet types restrict the range of feasible skin flap thicknesses to a maximum of 6 mm. Further we conclude that retention forces between 0.23 and 0.4 N could provide the appropriate trade-off between the risk of losing device fixation and of causing skin irritations. We recommend measuring the retention force in all patients.

The aim of this study was to measure how age affects the speech recognition threshold (SRT₅₀) of the Oldenburg Sentence Test (OLSA) and the listening effort at the corresponding signal-to-noise ratio (SNR_cut). The study also investigated the effect of the spatial configuration of sound sources and noise signals on SRT₅₀ and SNR_cut. To achieve this goal, the study used olnoise and icra5 noise presented from one or more spatial locations from the front and back. Ninety-nine participants with age-related hearing loss in the 18–80 years age range, specifically in the 18–30, 31–40, 41–50, 51–60, 61–70, and 71–80 age groups, participated in this study. Speech recognition and listening effort in noise were measured and compared between the different age groups, different spatial sound configurations and noise signals. Speech recognition in noise decreased with age and became significant from the age group of 50–51. The decrease in SRT₅₀ with age was greater for icra5 noise than for olnoise. For all age groups, SRT₅₀ and SNR_cut were better for icra5 noise than for olnoise. The measured age-related reference data for SRT₅₀ and SNR_cut can be used in further studies in listeners with age-related hearing loss and hearing aid or implant users.

Speech perception in noise is challenging and is improved by binaural hearing. Since signal processing of assistive hearing devices often modifies or masks the peripheral binaural head-shadow or better-ear effects, central binaural processing should be measured separately. In a prospective study, 10 listeners with normal hearing were tested with the German matrix sentence test in a set-up with two loudspeakers located at opposite angles in the horizontal plane with respect to S₀N₀. The speech reception threshold (SRT) was investigated depending on the separation angle between speech and noise. The lowest (best) SRT was obtained for a separation of target and interfering source from S₀N₀ at an angle of about S_±60°N_∓60°. The derived normative curve was comparable to SRTs predicted by the binaural-speech-intelligibility-model. The systematic separation of signal and noise showed a significant improvement in speech intelligibility for normal-hearing people even for small separation angles. This experimental setting was verified. This study aimed to assess the effect of small sound source separation on binaural hearing and speech perception.

For many cochlear implant (CI) users, frequency discrimination is still challenging. We studied the effect of frequency differences relative to the electrode frequency bands on pure tone discrimination. A single-center, prospective, controlled, psychoacoustic exploratory study was conducted in a tertiary university referral center. Thirty-four patients with Cochlear Ltd. and MED-EL CIs and 19 age-matched normal-hearing control subjects were included. Two sinusoidal tones were presented with varying frequency differences. The reference tone frequency was chosen according to the center frequency of basal or apical electrodes. Discrimination abilities were psychophysically measured in a three-interval, two-alternative, forced-choice procedure (3I-2AFC) for various CI electrodes. Hit rates were measured, particularly with respect to discrimination abilities at the corner frequency of the electrode frequency-bands. The mean rate of correct decision concerning pitch difference was about 60% for CI users and about 90% for the normal-hearing control group. In CI users, the difference limen was two semitones, while normal-hearing participants detected the difference of one semitone. No influence of the corner frequency of the CI electrodes was found. In CI users, pure tone discrimination seems to be independent of tone positions relative to the corner frequency of the electrode frequency-band. Differences of 2 semitones can be distinguished within one electrode.