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Papers by Norbert Dillier
Journal of hearing science, 2011
To evaluate all aspects of binaural signal processing algorithms, an objective measure of how the... more To evaluate all aspects of binaural signal processing algorithms, an objective measure of how they affect spatial perception is required. We are developing such a measure using a data-driven approach based on virtual acoustics and models of binaural signal processing of the auditory system. We present a brief overview of the methods and models that we use to study spatial perception. We discuss the binaural cues of realistic signals in more detail, and demonstrate the importance of interaural coherence as a binaural cue. We conclude with an outlook on our future work.
Acta Oto-laryngologica, 1990
Based on a single-chip DSP (TMS320C25, Texas Instruments) a programmable batteryoperated sound pr... more Based on a single-chip DSP (TMS320C25, Texas Instruments) a programmable batteryoperated sound processor with a digital encoder interface for the Nucleus-22 cochlear implant (CI) was built. The number of quasi-simultaneously addressed electrodes is only limited by the selected pulse width and the maximum rate of stimulation and can be as high as 10 electrodes at 300Hz repetition rate. Implementation of various processing strategies (formant or channel vocoder, filterbank, zero crossings, etc.) is possible as well as sophisticated adaptive noise reduction. Programs and stimulation parameters are stored in electrically erasable memory and may be updated via a host computer. The built-in analog output may be used for single-channel stimulation or acoustic verifications of the sound processing algorithms. The power consumption with current 16K word data memory and at maximum stimulation rate is about 1 Watt, which necessitates recharging of batteries after 11 h.
Annals of Otology, Rhinology, and Laryngology, Jun 1, 1990
The correlation between inner ear pressure and cochlear function was investigated in guinea pigs ... more The correlation between inner ear pressure and cochlear function was investigated in guinea pigs with unilaterally obliterated endolymphatic sacs and ducts. In 11 animals that developed endolymphatic hydrops, auditory thresholds as monitored by auditory evoked action potentials had increased with recruitment. Most of these animals also experienced episodes of spontaneous nystagmus. In control ears endolymphatic pressure did not differ more than 0.5 ern H20 from perilymphatic pressure. In six of 11 hydropic ears, endolymphatic pressure was more than 0.5 cm H20 higher than perilympathic pressure; auditory thresholds in all these ears had deteriorated within 2 weeks before pressure recording. No further hearing deterioration within this period was noted in five hydropic ears with endolymphatic pressure equal to or lower than perilymphatic pressure. Endolympathic-perilymphatic pressure gradients may contribute to auditory threshold increase in endolymphatic hydrops, but are not its only cause.
Annals of Otology, Rhinology, and Laryngology, 1987
Hearing devices are mostly tested using controlled laboratory environments. These feature simplif... more Hearing devices are mostly tested using controlled laboratory environments. These feature simplified auditory representations of the real conditions under which the hearing devices will perform once released, such as one speech signal played from one loudspeaker plus a noise signal playing from another loudspeaker. It can however be insufficiently realistic for some of the processing included in the devices. In order to circumvent this limitation, Virtual Sound Environments (VSE) can be used to simulate complex sound fields using headphones or arrays of loudspeakers, and thus to offer more realistic conditions than most common hearing device evaluation protocols. In this paper, a hearing device algorithm based on Interaural Level Differences (ILD) was evaluated using Binaural Room Impulse Responses (BRIR, used here as a reference), and artificial room effects reproduced via either Higher Order Ambisonics (HOA) or Vector-Based Amplitude Panning (VBAP). Results show that the algorithm...
The realization of a hearing prosthesis which provides sensory deaf patients with improved speech... more The realization of a hearing prosthesis which provides sensory deaf patients with improved speech discrimination ability and better communication possibilities is based upon the following hypothesis: A neurosensory deaf patient with at least a partially intact auditory nerve would perceive acoustic Signals if an activation pattern equivalent to the pattern in a normal ear could be reproduced artificially in his auditory nerve. A model of the peripheral auditory System has been reviewed and adapted to new physiological data to explain differences in the excitation patterns of Single auditory nerve fibers between acoustic and electrical Stimulation. Experiments with electrical Stimulation in the external ear canal and on the promontory in 3o deaf patients and 15 normal hearing subjects have shown hearing sensations in more than So % of the deaf patients although the thresholds of discomfort were very close or even below the thresholds of hearing. Extended evaluation tests with a 5o ye...
Cochlear implants (CIs) were originally aimed at restoring speech perception for patients with pr... more Cochlear implants (CIs) were originally aimed at restoring speech perception for patients with profound hearing loss. Many postlingually deafened CI patients report that music is not well perceived while others enjoy it. Music consists of complex sounds composed of tones with harmonic structure of overtones and temporal fine structure. The harmonic structure is not preserved by the current standard (Std) ACE (advanced combination encoders) mapping and the temporal fine structure is not well encoded. The mapping is believed to produce distortion due to compression oin the low frequency range. In 2008 we proposed two new semitone (Smt) mappings (Smt-LF and Smt-MF) in two frequency ranges (130-1502 Hz and 440-5040 Hz) respectively (Omran et al. 2008). Smt mapping is expected to preserve the harmonic structure representation of overtones and this may improve melody recognition with CIs. In this paper two psychoacoustic experiments (melody contour identification (MCI) (Galvin et al. 2007) and instrument recognition (IR)) were conducted with three different conditions (Std, Smt-MF and Smt-LF mappings) with CI recipients by streaming processed stimuli directly to the implant. The MCI test included five patterns (rising-rising falling-flat-falling rising-falling). Each pattern consisted of five tones; each tone had a fundamental frequency and four overtones. The lowest fundamental frequency of each pattern is called "root". Signals had two different roots A3 (220 Hz) and A4 (440 Hz). Proposed nine patterns with three roots (A3, A4 and A5) by Galvin et al. (2007) were examined in a pilot test. This test took a long time and the preliminary results showed a possibility to reduce the number of patterns to five and eliminate the fifth octave root (A5). In the IR test, four pairs of instruments (Trumpet and Trombone, Flute and Clarinet, Violin and Cello, Guitar and Piano) from four groups (Brass, Woodwind, Struck and String instruments) respectively were used. MCI and IR tests were conducted with 8 CI recipients. Results from MCI tests showed an improvement with Smt mapping in respect to Std mapping or at least similar results. However, wrong identification occurred with notes having filtered out partials. CI recipients showed an increase in identifying melody contour patterns with Smt mappings. Instrument identification performance decreased with semitone mappings.
In today's cochlear implant systems, the signal intensity is usually encoded directly into the st... more In today's cochlear implant systems, the signal intensity is usually encoded directly into the stimulation level of the charge-balanced biphasic stimuli. One of the main factors limiting the spatial resolution is the electric field spread. This resolution is further compromised with increasing stimulation intensity, since the electric field spread is expected to increase accordingly. One possible alternative to minimize the electric field spread would be to use the stimulation rate to encode the signal intensity, while keeping the stimulation level constant.The present study investigates the accompanying change in the electric field spread when using either the stimulation rate (at a constant stimulation level) or stimulation level (at a constant stimulation rate) to achieve the same change in loudness, with the hypothesis that the former results in less changes in the electric field spread compared to the latter. Psychophysical forward masking functions were measured for three masker rate/level combinations: Firstly, the masker (e11, 500ms) was loudness matched at a comfortable level for either 250Hz or 2000Hz (at stimulation levels L250 and L2000 respectively, typically L2000 < L250). Additionally, the masker was set at 250Hz and L2000, corresponding to a lower loudness percept. The masked thresholds of a 250Hz 20ms probe, presented 4ms after the end of the masker, were then measured for locations either side of e11, in an adaptive 2down-1up 3IFC task.Results with 5 CI subjects indicate a greater increase in the amount of forward masking when the stimulation level was changed from L2000 to L250 (both at 250Hz), compared to when the stimulation rate was changed from 250Hz to 2000Hz (both at 2000Hz), supporting the hypothesis. The implications of these results will be discussed.
Ziel: Diese Studie untersucht Aspekte der Musikwahrnehmungsfähigkeit von Kindern, Jugendlichen un... more Ziel: Diese Studie untersucht Aspekte der Musikwahrnehmungsfähigkeit von Kindern, Jugendlichen und Erwachsenen mit Cochlea-Implantaten (CI) in Abhängigkeit von musikalischem Kontext, Frequenzbereich, Versorgungsmodalität (mono-vs. bilateral) und Alter bei der Implantation. Methode: Drei Experimente wurden durchgeführt, bei denen jeweils eine Testsequenz im Vergleich zu einer Referenzsequenz von Tonfolgen einer synthetisierten Klarinette präsentiert wurden. Die Aufgabe der Probanden bestand darin, die Sequenzen als gleich oder ungleich zu beurteilen. Experiment 1 beinhaltete, eine aufsteigende Tonhöhenänderung (0, 1, 2, 3 oder 4 Halbtöne) im zweiten von drei aufeinander folgenden Tönen in der Testsequenz zu detektieren. Experiment 2 untersuchte die Erkennung feiner Tonhöhenänderungen mit an-und absteigenden Fünftonsequenzen, die in einem melodischen Kontext (Dur-und Moll-Dreiklänge mit entsprechenden 3-und 4-Halbtonzusammensetzungen) dargeboten wurden. Bei Experiment 3 wurden, anstelle von Fünftonsequenzen, lediglich drei Töne in aufsteigender Abfolge präsentiert. Ergebnisse: Experiment 1 zeigte, dass die Fähigkeit von CI-Trägern, Tonhöhenänderungen zu detektieren, von der Grössenordnung der Variation abhängt. Alle CI-Träger konnten grössere Tonhöhenänderungen im Vergleich zu kleineren zuverlässiger wahrnehmen. Dennoch konnten alle Probandengruppen eine Tonhöhenänderung von einem Halbton oberhalb der Rateschwelle detektieren, wobei Kinder und Jugendliche tendenziell besser abschnitten als Erwachsene. Dies traf insbesondere für kleinere Tonhöhenänderungen sowie die tieferen Frequenzbereiche zu. Bei Experiment 2 und 3 wiesen die CITräger Defizite in allen Messbedingungen auf. Die Resultate aller Probanden lagen unterhalb der Rateschwelle. Die Ergebnisse zeigten eine zunehmende Verschlechterung mit abnehmendem Frequenzbereich. Zudem korrelierten die Messergebnisse mit den Angaben im Fragebogen zur musikalischen Erfahrung. Geringe Tonhöhenänderungen konnten, unabhängig vom musikalischen Kontext, von denjenigen CI-Trägern detektiert werden, die regelmässig ein Musikinstrument spielen.
International Journal of Audiology, Dec 29, 2021
Objective: This study compared two different versions of an electrophysiology-based softwareguide... more Objective: This study compared two different versions of an electrophysiology-based softwareguided cochlear implant fitting method with a procedure employing standard clinical software. The two versions used electrically evoked compound action potential (ECAP) thresholds for either five or all twenty-two electrodes to determine sound processor stimulation level profiles. Objective and subjective performance results were compared between software-guided and clinical fittings. Design: Prospective, double-blind, single-subject repeated-measures with permuted ABCA sequences. Study sample: 48 post linguistically deafened adults with 15 years of severe-to-profound deafness who were newly unilaterally implanted with a Nucleus device. Results: Speech recognition in noise and quiet was not significantly different between software-guided and standard methods, but there was a visit/learning-effect. However, the 5-electrode method gave scores on the SSQ speech subscale 0.5 points lower than the standard method. Clinicians judged usability for all methods as acceptable, as did subjects for comfort. Analysis of stimulation levels and ECAP thresholds suggested that the 5-electrode method could be refined. Conclusions: Speech recognition was not inferior using either version of the electrophysiology-based software-guided fitting method compared with the standard method. Subject-reported speech perception was slightly inferior with the five-electrode method. Software-guided methods saved about 10 min of clinician's time versus standard fittings.
Progress in Brain Research, 1993
The following processing strategies have been implemellled on an expcrimclllal laboratory systcm ... more The following processing strategies have been implemellled on an expcrimclllal laboratory systcm of a cochlear implant digital spcec h processor (CiDSP) for the Nucleus 2:!•channel cochlea r prosthesis. The first approa-.:h (PES. Pilch ExCIted Sa mpler) is based on the max.imum peak channel vo-.:oder concept whereby the time-varying spectral energy of a number of freque ncy bands is transformed into eleclricalslimulation pa rameters for up 10 22 electrodes. The pu lse rate at any electrode is controlled by the voice pitch of the input ~peech signal. The seco nd approach (C IS, Cl)nlinuou) Interleaved Sampler) uSeS a stimulation pulSe rale which is inuependclII 'of the input signa l. The algorithm continuo u~ly scans all)pccified frequency bands (typically be:tween four and :!:!) and salllpl~s their energy levels. As only one electrode can be stimu lated at any instance of time. the maxi mally achkvable rate of stimulation is limited by the: require:d stimulus pulse widths (determine'" individua ll y fo r e::u.:h subject)and so me addi• lionalconstraints and parameters. A numbt!r of va riations of t he C IS approach have, therefore , been implemented whIch euher maximize the number of quasi-simuhaneous stimulati o n channds or the pulse ra te on a reduced numbcr of electrodes. Evaluation experiments with five experienced cochlear implant users sho\ved signi ficantl y better pt!rformance in co nso nant ide ntification tests with the new pro-.:essing strategies than wilh the subjects' own wearable speech proc~ssors; improvements in vOwel identificati on la)ks were rarely obsened. ~l odificallons of the basic PES-and CIS strategies resulted in large va riatio ns of identifi ca tion score~. Info rmati on transmission anal ysis of confusio n matrices reveall!d a rather compll!x pattern across conditions and sp«:ch features. Optimiza!lon and fine • tunmg of processing parameters for Ihe~e codi ng strategies will reqUire more data both from specch klcntification and discrimination evaluations and from psychoph)'sical e'<Pt!riments.
IEEE Transactions on Biomedical Engineering, Aug 1, 2022
This study aimed to investigate the relationship between cochlear implant (CI) electrode distance... more This study aimed to investigate the relationship between cochlear implant (CI) electrode distances to the cochlea's inner wall (the modiolus) and electrical impedance measurements made at the CI's electrode contacts. We introduced a protocol for "three-point impedances" in which we recorded bipolar impedances in response to monopolar stimulation at a neighboring electrode. We aimed to assess the usability of three-point impedances and two existing CI impedance measurement methods (monopolar and four-point impedances) for predicting electrode positioning during CI insertion. Methods: Impedances were recorded during stepwise CI electrode array insertions in cadaveric human temporal bones. The positioning of the electrodes with respect to the modiolus was assessed at each step using cone beam computed tomography. Linear mixed regression analysis was performed to assess the relationship between the impedances and electrode-modiolar distances. The experimental results were compared to clinical impedance data and to an existing lumped-element model of an implanted CI. Results: Three-point and four-point impedances strongly correlated with electrode-modiolar distance. In contrast, monopolar impedances were only minimally affected by changes in electrode positioning with respect to the modiolus. An overall model specificity of 62% was achieved when incorporating all impedance parameters. This specificity could be increased beyond 73% when prior expectations of electrode positioning were incorporated in the model. Conclusion: Three-point and four-point impedances are promising measures to predict electrode-modiolar distance in real-time Manuscript
Springer eBooks, 1985
We have developed a system of classification using a relatively short list of code numbers derive... more We have developed a system of classification using a relatively short list of code numbers derived from the international code. This enables us to determine the frequency with which any one audiological or otological diagnosis is made, as well as the frequency of combinations of these diagnoses. It is hoped that this system will help the user to determine the relationship between disease entities in an audiological caseload. Furthermore, it may render possible a comparison of diagnoses and therapeutic results between different centers.
Otolaryngologic Clinics of North America, Feb 1, 1983
Ear Research Japan, 1983
Perilymphatic Oxygenation and Dynamic Pressure Changes by Reduced Vascular Supply to the Inner Ea... more Perilymphatic Oxygenation and Dynamic Pressure Changes by Reduced Vascular Supply to the Inner Ear K. Nagahara*, N. Dillier, U. Fisch, S. Kishimoto** * ENT Department , Kyoto National Hospital ** ENT Department , University of Zurich, Switzerland The effect of making granulation and resulting fibrotic changes in the internal auditory canal (IAC) following powdering of metyl methacrylate was examined in 24 special pyrogen free cats. Six months prior to the measurements the IAC was opened by the middle fossa approach and the superior wall of the meatus was removed . Metyl methacrylate powder was inserted into the meatus . The perilymphatic oxygen tension by the polarographic technique, hydrostatic pressure by servo-controlled micropipet system, CM, AP, were recorded. The initial perilymphatic PO2 values of the sides of reduced vascular supply and the contralateral control ears werre 11 .8±3.8 mmHg and 23.3 ±6.7 mmHg, respectively. Sensorineural hearing loss (high tone loss of on avera...
Journal of Biomedical Science and Engineering, 2018
A novel cochlear implant coding strategy based on the neural excitability has been developed and ... more A novel cochlear implant coding strategy based on the neural excitability has been developed and implemented using Matlab/Simulink. Unlike present day coding strategies, the Excitability Controlled Coding (ECC) strategy uses a model of the excitability state of the target neural population to determine its stimulus selection, with the aim of more efficient stimulation as well as reduced channel interaction. Central to the ECC algorithm is an excitability state model, which takes into account the supposed refractory behaviour of the stimulated neural populations. The excitability state, used to weight the input signal for selecting the stimuli, is estimated and updated after the presentation of each stimulus, and used iteratively in selecting the next stimulus. Additionally, ECC regulates the frequency of stimulation on a given channel as a function of the corresponding input stimulus intensity. Details of the model, implementation and results of benchtop plus subjective tests are presented and discussed. Compared to the Advanced Combination Encoder (ACE) strategy, ECC produces a better spectral representation of an input signal, and can potentially reduce channel interactions. Pilot test results from 4 CI recipients suggest that ECC may have some advantage over ACE for complex situations such as speech in noise, possibly due to ECC's ability to present more of the input spectral contents compared to ACE, which is restricted to a fixed number of maxima. The ECC strategy represents a neurophysiological approach that could potentially improve the perception of more complex sound patterns with cochlear implants.
Annals of Otology, Rhinology & Laryngology, 2001
A method is described that allows, for the first time, intraoperative vibration modes assessment ... more A method is described that allows, for the first time, intraoperative vibration modes assessment of the acoustically stimulated stapes by means of scanning laser Doppler interferometry (LDI). The study was designed to answer the following questions: 1) Is LDI practical for taking measurements during surgery? 2) Are the results comparable to the findings in temporal bone preparations? and 3) Do the vibration characteristics of the stapes change after the posterior incudal ligament is detached from the incus? Seven patients with profound bilateral hearing loss who were undergoing cochlear implantation were included in the study. The measurement system was easily applicable for intraoperative measurements and allowed contact-free analysis with very high accuracy. No major differences in the results from the live human subjects and temporal bone preparations were observed. The stapes movement was predominantly pistonlike at the lower frequencies and became complex at higher frequencies....
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Videos by Norbert Dillier
Papers by Norbert Dillier