Impact of a moving noise masker on speech perception in cochlear implant users

Objectives: Previous studies investigating speech perception in noise have typically been conducted with static masker positions. The aim of this study was to investigate the effect of spatial separation of source and masker (spatial release from masking, SRM) in a moving masker setup and to evaluate the impact of adaptive beamforming in comparison with fixed directional microphones in cochlear implant (CI) users. Design: Speech reception thresholds (SRT) were measured in S0N0 and in a moving masker setup (S0Nmove) in 12 normal hearing participants and 14 CI users (7 subjects bilateral, 7 bimodal with a hearing aid in the contralateral ear). Speech processor settings were a moderately directional microphone, a fixed beamformer, or an adaptive beamformer. The moving noise source was generated by means of wave field synthesis and was smoothly moved in a shape of a half-circle from one ear to the contralateral ear. Noise was presented in either of two conditions: continuous or modulated. Results: SRTs in the S0Nmove setup were significantly improved compared to the S0N0 setup for both the normal hearing control group and the bilateral group in continuous noise, and for the control group in modulated noise. There was no effect of subject group. A significant effect of directional sensitivity was found in the S0Nmove setup. In the bilateral group, the adaptive beamformer achieved lower SRTs than the fixed beamformer setting. Adaptive beamforming improved SRT in both CI user groups substantially by about 3 dB (bimodal group) and 8 dB (bilateral group) depending on masker type. Conclusions: CI users showed SRM that was comparable to normal hearing subjects. In listening situations of everyday life with spatial separation of source and masker, directional microphones significantly improved speech perception with individual improvements of up to 15 dB SNR. Users of bilateral speech processors with both directional microphones obtained the highest benefit

Speech perception in noise : impact of directional microphones in users of combined electric-acoustic stimulation

Objectives: Combined electric-acoustic stimulation (EAS) is a well-accepted therapeutic treatment for cochlear implant (CI) users with residual hearing in the low frequencies but severe to profound hearing loss in the high frequencies. The recently introduced SONNETeas audio processor offers different microphone directionality (MD) settings and wind noise reduction (WNR) as front-end processing. The aim of this study was to compare speech perception in quiet and noise between two EAS audio processors DUET 2 and SONNETeas, to assess the impact of MD and WNR on speech perception in EAS users in the absence of wind. Furthermore, subjective rating of hearing performance was registered. Method: Speech perception and subjective rating with SONNETeas or DUET 2 audio processor were assessed in 10 experienced EAS users. Speech perception was measured in quiet and in a diffuse noise setup (MSNF). The SONNETeas processor was tested with three MD settings omnidirectional/natural/adaptive and with different intensities of WNR. Subjective rating of auditory benefit and sound quality was rated using two questionnaires. Results: There was no significant difference between DUET 2 and SONNETeas processor using the omnidirectional microphone in quiet and in noise. There was a significant improvement in SRT with MD settings natural (2.2 dB) and adaptive (3.6 dB). No detrimental effect of the WNR algorithm on speech perception was found in the absence of wind. Sound quality was rated as “moderate” for both audio processors. Conclusions: The different MD settings of the SONNETeas can provide EAS users with better speech perception compared to an omnidirectional microphone. Concerning speech perception in quiet and quality of life, the performance of the DUET 2 and SONNETeas audio processors was comparable

Sensitivity to interaural time differences and localization accuracy in cochlear implant users with combined electric-acoustic stimulation

Objectives: In this study, localization accuracy and sensitivity to acoustic interaural time differences (ITDs) in subjects using cochlear implants with combined electric-acoustic stimulation (EAS) were assessed and compared with the results of a normal hearing control group. Methods: Eight CI users with EAS (2 bilaterally implanted, 6 unilaterally implanted) and symmetric binaural acoustic hearing and 24 normal hearing subjects participated in the study. The first experiment determined mean localization error (MLE) for different angles of sound incidence between ± 60° (frontal and dorsal presentation). The stimuli were either low-pass, high-pass or broadband noise bursts. In a second experiment, just noticeable differences (JND) of ITDs were measured for pure tones of 125 Hz, 250 Hz and 500 Hz (headphone presentation). Results: Experiment 1: MLE of EAS subjects was 8.5°, 14.3° and 14.7°, (low-, high-pass and broadband stimuli respectively). In the control group, MLE was 1.8° (broadband stimuli). In the differentiation between sound incidence from front and back, EAS subjects performed on chance level. Experiment 2: The JND-ITDs were 88.7 μs for 125 Hz, 48.8 μs for 250 Hz and 52.9 μs for 500 Hz (EAS subjects). Compared to the control group, JND-ITD for 125 Hz was on the same level of performance. No statistically significant correlation was found between MLE and JND-ITD in the EAS cohort. Conclusions: Near to normal ITD sensitivity in the lower frequency acoustic hearing was demonstrated in a cohort of EAS users. However, in an acoustic localization task, the majority of the subjects did not reached the level of accuracy of normal hearing. Presumably, signal processing time delay differences between devices used on both sides are deteriorating the transfer of precise binaural timing cues

Click-noise observed with moveable magnets in cochlear implants: case report and acoustic measurements

Severe to profound hearing loss and deafness are treated with a cochlear implant (CI) fitting. Today, the indication for CI fitting in adult patients with single sided deafness (SSD) has been recognized and financed in Germany.A magnet in the center of the CI receiver coil attaches the transmitter coil, which is worn on the outside of the head. CI from the manufacturers Advanced Bionics (Valencia, California, USA), Cochlear (Macquarie, Australia), and MED-EL (Innsbruck, Austria) are equipped with movable magnets so that MRI examinations in CI patients can be performed without side effects and without the risk of a magnet dislocation.For a 16-year-old male adolescent presented in this case report, who suffered from SSD, the indication for a CI was established after detailed diagnostics and a CI stimulator was implanted. During the postoperative period, the patient described a click-noise of the CI magnet, which was caused by jerky movements of the head (head shaking) as well as when walking. This click-noise was perceived as a severe impairment. Despite intensive rehabilitation, no hearing success was achieved due to the click-noise, which was perceived as stressful. Finally, an explantation was performed at the patient's request.The manufacturer checked the explant and could not find any indications of functional disorders. Acoustic measurements were performed on the explant at Technical University of Darmstadt in an anechoic chamber by "shaking" the explant repeatedly with a test set-up developed for this purpose. The equivalent continuous sound pressure level (Leq) measured at a distance of 100 mm was 29 dB above 1.5 kHz with a peak level (Lpeak) of 67.2 dB. An implant demonstration specimen was investigated as well, where a Leq of 31 dB and an Lpeak of 66.4 dB were measured using the same measurement setup.In SSD patients, sound - similar to bone conducting hearing aids - could be transcranially transmitted via bone conduction as well as via soft tissue, so that the normal hearing ear can perceive the click-noise of the CI magnet. The click-noise showed dominant sound pressures at frequencies above 1.5 kHz. In this frequency range, bone and soft tissue conduct the sound particularly well. In addition, the transcranial attenuation at 1.5 kHz is around 0 dB, which may also contribute to the hearing of the click-noise through the healthy ear. In order to reduce click-noise, the CI model under investigation has now been modified in terms of design.Conclusion: When advising SSD patients for a CI fitting, the possible occurrence of click-noise in the opposite ear should be pointed out.Schwerer bis hochgradiger Hörverlust und Taubheit werden mit einer Cochlea-Implantat-(CI)-Versorgung behandelt. Inzwischen wird die Indikation zur CI-Versorgung auch bei erwachsenen Patienten mit einseitiger Taubheit (engl.: single sided deafness , SSD) in Deutschland anerkannt und finanziert.Ein Magnet im Zentrum der CI-Empfangsspule fixiert die Sendespule, die außen am Kopf getragen wird. Dieser Magnet ist bei den Herstellern Advanced Bionics (Valencia, Kalifornien, USA), Cochlear (Macquarie, Australien) und MED-EL (Innsbruck, Österreich) beweglich, damit MRT-Untersuchungen bei CI-Patienten ohne Nebenwirkungen und ohne Gefahr einer Magnetdislokation durchgeführt werden können.Bei einem in diesem Fallbericht vorgestellten 16 Jahre alten männlichen Jugendlichen, der unter einer einseitigen Taubheit litt, wurde nach ausführlicher Diagnostik die Indikation für ein CI gestellt und ein CI-Stimulator implantiert. Im Verlauf nach der Operation schilderte der Patient Klickgeräusche des CI-Magneten, die durch ruckartige Bewegungen des Kopfes (Kopfschütteln) sowie beim Gehen entstanden und als starke Beeinträchtigung empfundenen wurden. Da sich neben dem als belastend empfundenem Geräusch trotz intensiver Rehabilitation kein Hörerfolg einstellte, wurde schließlich auf Wunsch des Patienten eine Explantation durchgeführt.Der Hersteller überprüfte das Explantat und konnte keine Hinweise auf Funktionsstörungen feststellen. Das Explantat wurde an der TU Darmstadt akustisch in einem reflexionsarmen Raum vermessen, indem es mit einem für diesen Zweck entwickelten Versuchsaufbau wiederholgenau "geschüttelt" wurde, um ein Klickgeräusch zu provozieren. Der in 100 mm Abstand gemessene äquivalente Dauerschallpegel (Leq) betrug oberhalb von 1,5 kHz 29 dB mit einem Spitzenpegel (Lpeak) von 67,2 dB. Bei einem ebenfalls akustisch untersuchten Implantat-Demonstrationsmuster wurden in analoger Messanordnung ein Leq von 31 dB und ein Lpeak von 66,4 dB gemessen.Bei SSD-Patienten könnte Schall - ähnlich wie bei knochenverankerten Hörimplantaten - über Knochenleitung sowie über Weichgewebe transkraniell übertragen werden, so dass das normalhörende Ohr die Klickgeräusche des CI-Magneten wahrnehmen kann. Das Klickgeräusch zeigte dominierende Schalldrücke bei Frequenzen oberhalb von 1,5 kHz. In diesem Frequenzbereich leiten Knochen und Weichgewebe den Schall besonders gut. Zusätzlich liegt die transkranielle Dämpfung bei 1,5 kHz um 0 dB, was das Hören der Klickgeräusche durch das gesunde Ohr ebenfalls begünstigen kann. Um Klickgeräusche zu reduzieren, wurde das untersuchte CI-Modell inzwischen konstruktiv geändert.Fazit: Bei der Beratung von SSD-Patienten für eine CI-Versorgung sollte auf das mögliche Auftreten von Klickgeräuschen im Gegenohr hingewiesen werden

Interleaved acoustic environments: impact of an auditory scene classification procedure on speech perception in cochlear implant users

Clinical speech perception tests with simple presentation conditions often overestimate the impact of signal preprocessing on speech perception in complex listening environments. A new procedure was developed to assess speech perception in interleaved acoustic environments of different complexity that allows investigation of the impact of an automatic scene classification (ASC) algorithm on speech perception. The procedure was applied in cohorts of normal hearing (NH) controls and uni- and bilateral cochlear implant (CI) users. Speech reception thresholds (SRTs) were measured by means of a matrix sentence test in five acoustic environments that included different noise conditions (amplitude modulated and continuous), two spatial configurations, and reverberation. The acoustic environments were encapsulated in a randomized, mixed order single experimental run. Acoustic room simulation was played back with a loudspeaker auralization setup with 128 loudspeakers. 18 NH, 16 unilateral, and 16 bilateral CI users participated. SRTs were evaluated for each individual acoustic environment and as mean-SRT. Mean-SRTs improved by 2.4 dB signal-to-noise ratio for unilateral and 1.3 dB signal-to-noise ratio for bilateral CI users with activated ASC. Without ASC, the mean-SRT of bilateral CI users was 3.7 dB better than the SRT of unilateral CI users. The mean-SRT indicated significant differences, with NH group performing best and unilateral CI users performing worse with a difference of up to 13 dB compared to NH. The proposed speech test procedure successfully demonstrated that speech perception and benefit with ASC depend on the acoustic environment