Effects of temporal fine structure preservation on spatial hearing in bilateral cochlear implant users.

Typically, the coding strategies of cochlear implant audio processors discard acoustic temporal fine structure information (TFS), which may be related to the poor perception of interaural time differences (ITDs) and the resulting reduced spatial hearing capabilities compared to normal-hearing individuals. This study aimed to investigate to what extent bilateral cochlear implant (BiCI) recipients can exploit ITD cues provided by a TFS preserving coding strategy (FS4) in a series of sound field spatial hearing tests. As a baseline, we assessed the sensitivity to ITDs and binaural beats of 12 BiCI subjects with a coding strategy disregarding fine structure (HDCIS) and the FS4 strategy. For 250 Hz pure-tone stimuli but not for broadband noise, the BiCI users had significantly improved ITD discrimination using the FS4 strategy. In the binaural beat detection task and the broadband sound localization, spatial discrimination, and tracking tasks, no significant differences between the two tested coding strategies were observed. These results suggest that ITD sensitivity did not generalize to broadband stimuli or sound field spatial hearing tests, suggesting that it would not be useful for real-world listening.

Assessment of speech perception and communication skills in adolescents with cochlear implants for pre- and peri-lingual deafness.

OBJECTIVE: This study aimed to assess speech perception and communication skills in adolescents between ages 8 and 18 that received cochlear implants for pre- and peri-lingual deafness. METHODS: We studied 15 adolescents, aged 12 to 23 years, with late cochlear implantation. Speech perception was assessed with the Bishop sentences test and a memory number sequence test at 3-9 years after cochlear implantation. A questionnaire completed retrospectively was used to investigate communication skills pre- and post implantation. RESULTS: Six individuals achieved grammar comprehension scores comparable to children 8-10 years old with normal hearing; only 3 individuals achieved a percentile rank higher than 50% in the memory number sequence test. The self-reported communication skills improved after cochlear implantation in all adolescents. CONCLUSIONS: Speech perception skills of adolescents with late implantation for pre- and peri-lingual deafness are typically inferior to those of children with normal hearing at the age of 10. However, when the evaluation of the cochlear implant outcome was broadened with the use of a questionnaire, many individuals reported that they participated more actively in conversations, spoke more actively to unknown individuals, and were more easily understood by others.

The tolerance of ambiguity in late cochlear-implanted pre-lingually deaf juveniles.

OBJECTIVES: To examine the ambiguity tolerance, i.e. the ability to perceive new, contradictory and complex situations as positive challenges, of pre-lingually deafened adolescents who received a cochlear implant after their eighth birthday and to identify those dimensions of ambiguity tolerance which correlate significantly with specific variables of their oral communication. DESIGN AND SETTING: Clinical survey at an academic tertiary referral center. PARTICIPANTS AND MAIN OUTCOME MEASURES: A questionnaire concerning communication and subjectively perceived changes compared to the pre-cochlear implant situation was completed by 13 pre-lingually deafened patients aged between 13 and 23 years, who received their cochlear implants between the ages of 8 and 17 years. The results were correlated with the 'Inventory for Measuring Ambiguity Tolerance'. RESULTS: The patients showed a lower ambiguity tolerance with a total score of 134.5 than the normative group with a score of 143.1. There was a positive correlation between the total score for ambiguity tolerance and the frequency of 'use of oral speech', as well as between the subscale 'ambiguity tolerance towards apparently insoluble problems' and all five areas of oral communication that were investigated. Comparison of two variables of oral communication, which shows a significant difference pre- and postoperatively, yields a positive correlation with the subscale 'ambiguity tolerance towards the parental image'. CONCLUSIONS: Pre-lingually deafened juveniles with cochlear implant who increasingly use oral communication seem to regard the limits of a cochlear implant as an interesting challenge rather than an insoluble problem.

Instrument flight to the inner ear.

Surgical robot systems can work beyond the limits of human perception, dexterity and scale making them inherently suitable for use in microsurgical procedures. However, despite extensive research, image-guided robotics applications for microsurgery have seen limited introduction into clinical care to date. Among others, challenges are geometric scale and haptic resolution at which the surgeon cannot sufficiently control a device outside the range of human faculties. Mechanisms are required to ascertain redundant control on process variables that ensure safety of the device, much like instrument-flight in avionics. Cochlear implantation surgery is a microsurgical procedure, in which specific tasks are at sub-millimetric scale and exceed reliable visuo-tactile feedback. Cochlear implantation is subject to intra- and inter-operative variations, leading to potentially inconsistent clinical and audiological outcomes for patients. The concept of robotic cochlear implantation aims to increase consistency of surgical outcomes such as preservation of residual hearing and reduce invasiveness of the procedure. We report successful image-guided, robotic CI in human. The robotic treatment model encompasses: computer-assisted surgery planning, precision stereotactic image-guidance, in-situ assessment of tissue properties and multipolar neuromonitoring (NM), all based on in vitro, in vivo and pilot data. The model is expandable to integrate additional robotic functionalities such as cochlear access and electrode insertion. Our results demonstrate the feasibility and possibilities of using robotic technology for microsurgery on the lateral skull base. It has the potential for benefit in other microsurgical domains for which there is no task-oriented, robotic technology available at present.

Acoustic imaging of the human chest.

STUDY OBJECTIVES: A novel method for acoustic imaging of the human respiratory system is proposed and evaluated. DESIGN: The proposed imaging system uses simultaneous multisensor recordings of thoracic sounds from the chest wall, and digital, computer-based postprocessing. Computer simulations and recordings from a life-size gelatin model of the human thorax are used to evaluate the system in vitro. Spatial representations of thoracic sounds from 8-microphone and 16-microphone recordings from five subjects (four healthy male adults and one child with lung consolidation) are used to evaluate the system in vivo. RESULTS: Results of the in vitro studies show that sound sources can be imaged to within 2 cm, and that the proposed algorithm is reasonably robust with respect to changes in the assumed sound speed within the imaged volume. The images from recordings from the healthy volunteers show distinct patterns for inspiratory breath sounds, expiratory breath sounds, and heart sounds that are consistent with the assumed origin of the respective sounds. Specifically, the images support the concept that inspiratory sounds are produced predominantly in the periphery of the lung while expiratory sounds are generated more centrally. Acoustic images from the subject with lung consolidation differ substantially from the images of the healthy subjects, and localize the abnormality. CONCLUSIONS: Acoustic imaging offers new perspectives to explore the acoustic properties of the respiratory system and thereby reveal structural and functional properties for diagnostic purposes.

Computer-based lung sound simulation.

An algorithm for the simulation of normal and pathological lung sounds is developed. The simulation algorithm is implemented on a personal computer as well as on a digital signal processor system in real time. Normal, bronchial and tracheal breathing sounds can be generated, and continuous and discontinuous adventitious lung sounds can be added. The attributes of the individual sound components, such as loudness, frequency, duration or number of occurrences within one breathing cycle, are controlled by the user. The quality of the simulations is evaluated by sending audio tapes to 15 experienced pulmonary physicians for a formal assessment. Each tape contains five simulated lung sounds and five real lung sounds from a commercially available teaching tape, presented in random order. Simulated lung sounds are slightly better rated in terms of realism and signal quality when compared to the recordings from the teaching tape. The differences are, however, not significant. 13 out of the 15 physicians feel that computer-based lung sound simulators would be a useful and desirable teaching tool for auscultation courses.

Electromagnetic interference of bone-anchored hearing aids by cellular phones.

We report a case of electromagnetic interference between a bone-anchored hearing aid (BAHA) and a cellular phone. A 54-year-old women was successfully treated for severe mixed conductive and sensorineural hearing loss with a BAHA. Five years after implantation, the patient experienced a sudden feeling of dizziness, accompanied by a loud buzzing sound and by a sensation of head pressure while examining a digital mobile phone. During a subsequent experiment, the buzzing sound could be reproduced and was identified as electromagnetic interference between the BAHA and digital cellular phones. Seventeen adult BAHA users from our clinic participated in a subsequent survey. Of the 13 patients with some experience of digital cellular phones, 11 reported hearing annoying noises elicited by these devices. However, no other sensation, such as dizziness, was described. Owing to the increasing number of users of both hearing aids and cellular phones, the incidence of electromagnetic interference must be expected to increase as well. Although to date there is no evidence that such interference may be harmful or dangerous to users of conventional or bone-anchored hearing aids, unexpected interference can be a frightening experience.

Performance of compressed analogue (CA) and continuous interleaved sampling (CIS) coding strategies for cochlear implants in quiet and noise.

Speech understanding with compressed analogue (CA) and continuous interleaved sampling (CIS) coding strategies for cochlear implants was compared in quiet and in noise at signal-to-noise ratios (SNRs) of 15, 10 and 5 dB. The speech recognition of three experienced users of the Ineraid cochlear implant (CA coding strategy) was assessed using a set of sentence, vowel and consonant tests. Three weeks after the fitting of a CIS processor, the tests were repeated with the new device. Speech recognition scores for the sentence and consonant tests tended to be higher with the CIS processor in no or little noise, but lower in the test situations with less favourable SNRs, when compared to the CA processor (average score differences for the consonant test: +7.8% correct at 15 dB SNR; -6.8% correct at 5 dB SNR; p = 0.05). Results for the vowel test were slightly lower on average for the CIS processing strategy at all SNRs. A possible explanation for the differences in performance between CIS and CA in the consonant and sentence tests at different SNRs is the generally higher free-field threshold associated with the CA coding strategy, which may act as a single-channel noise suppression.

Digital signal processing (DSP) applications for multiband loudness correction digital hearing aids and cochlear implants.

Single-chip digital signal processors (DSPs) allow the flexible implementation of a large variety of speech analysis, synthesis, and processing algorithms for the hearing impaired. A series of experiments was carried out to optimize parameters of the adaptive beamformer noise reduction algorithm and to evaluate its performance in realistic environments with normal-hearing and hearing-impaired subjects. An experimental DSP system has been used to implement a multiband loudness correction (MLC) algorithm for a digital hearing aid. Speech tests in quiet and noise with 13 users of conventional hearing aids demonstrated significant improvements in discrimination scores with the MLC algorithm. Various speech coding strategies for cochlear implants were implemented in real time on a DSP laboratory speech processor. Improved speech discrimination performance was achieved with high-rate stimulation. Hybrid strategies incorporating speech feature detectors and complex decision algorithms are currently being investigated.

A novel real-time noise reduction system for the assessment of evoked otoacoustic emissions.

A novel noise reduction method and apparatus to be used in connection with the measurement of evoked otoacoustic emissions (EOAE) are presented. The noise reduction method is based on an adaptive noise canceller and requires a noise-only reference microphone placed in the vicinity of the OAE-probe. The method was implemented in real time on a custom built digital signal processing system using an Analog Devices ADSP-2181 digital signal processor. The system interfaces seamlessly with a commercial EOAE acquisition system. Results of a series of experiments show than noise reductions of 7-8 dB can be reached.

[New developments in hearing aid technology]. / Neuentwicklungen in der Hörgeräteversorgung.

The last decade has seen numerous and significant improvements in hearing aid technology. Digital hearing aids are becoming increasingly common and have already replaced a considerable portion of the hearing aids using the older analogue technology. Efficient noise reduction methods, most notably multi-microphone systems for hearing aids, can increase speech intelligibility in adverse listening situations and noisy environments. Accessories, such as e.g. wireless classroom communication systems (FM systems) and remote controls are becoming smaller and less visible. As a consequence of the increased complexity of modern hearing aids, however, hearing aid fitting has become considerably more complex.

[Bone anchored hearing aids (B.A.H.A.)]. / Erfahrungen mit dem teilimplantierten Knochenleitungshörgerät B.A.H.A.

Semi-implantable bone conduction hearing aids of the type Bone Anchored Hearing Aids (B.A.H.A.) consist of an external vibrator hearing aid that is attached to a titanium screw implanted in the mastoideal bone behind the ear by means of a transcutaneous connector. In this way sound waves are transmitted directly to the bones of the skull, from where they are conducted to the cochlea. The primary indication for a semi-implantable bone conduction hearing aid is hearing loss due to conduction failure that is not surgically correctable. This may be caused, e.g. by ear canal atresia and other malformations of the external auditory meatus and of the middle ear, by chronic ear infections or by persistent high grade conduction hearing impairment after radical mastoidectomy. Today B.A.H.A.'s largely replace the less convenient conventional bone conducting hearing aids as hearing glasses or hearing bands, in which a vibrator is pressed against the skull. In conduction hearing impairment on both ears B.A.H.A.'s can be implanted bilaterally and thus binaural hearing with sound source localisation are made possible. A novel application is in cases of unilateral deafness, where the device is implanted on the side of the deaf ear and the amplified sounds are transmitted through the skull to the side of the hearing ear. Here it serves as a substitute for a CROS hearing aid. In adults the implantation is performed under local anesthesia as an out-patient procedure. Implantation may be undertaken under general anesthesia on children after two years of age. In Berne, B.A.H.A. bone conduction hearing aids have been implanted in 112 patients (ages 2-82 years) in the past 13 years. The operations have proved simple and without intra-operative complications. The long-term post-operative incidence of complications was low. The transcutaneous screw caused only isolated cases of transient skin reactions or local infections. In 7% of cases, rejection of the implant or a traumatic loosening of the screw required a reimplantation procedure. Over 90% of patients reported themselves satisfied with their partially-implantable B.A.H.A. hearing aids.

[The cochlear implant--evolution of hearing and language with an artificial inner ear]. / Das Cochlea-Implantat--Entwicklung von Gehör und Sprache mit einem künstlichen Innenohr.

One of the most spectacular progresses in modern medicine is the possibility to replace a deaf ear, a sensory organ in total by an implantable electronic prosthesis, a so-called cochlear implant (CI). The CI stimulates the auditory nerve by electrical pulses and thus generates the sensation of hearing along the auditory pathway. One of the most impressive aspects of cochlear implantation is the fact that small children with profound deafness who were able a few years ago to learn spoken language only to very limited extent may achieve nowadays an almost normal language development. Duration and intensity of the training of listening and spoken language vary considerably as a function of etiology and time of deafness. Most important for the development of language is sufficient stimulation of the auditory pathway during early childhood. Early diagnosis of a severe to profound deafness is most important in order to fit hearing aids or a cochlear implant without a time delay. Affected children need intensive training by professionals specialized in education and speech therapy. Adults and adolescents who lost their hearing when language acquisition was established may understand spoken language only a few weeks after receiving a cochlear implant. Several individuals are able to use the telephone. Preliminary results after bilateral cochlear implantation of children and adults show advantages. Not only do these subjects report "better hearing with two CI as compared to hearing with one CI," but some of them developed directional hearing in a rather short time lag after fitting the second implant. And in addition they achieve better speech discrimination in environmental noise.

[Tinnitus]. / Tinnitus.

Tinnitus is an auditory perception without adequate external acoustic sources. The incidence of tinnitus in the general population is high, and can lead to total decompensation in some of the affected patients. Tinnitus is a symptom of an unspecific lesion of the ear or the central auditory system. In many cases, the cause of tinnitus can be inferred from the medical history and from the results of specific medical examines. Nevertheless, in many cases there is still no causal therapy available. As a result, for most patients approaches such as proper counselling, the fitting of hearing aids or tinnitus retraining therapy are adopted.

Towards a consensus on a hearing preservation classification system.

CONCLUSION: The comprehensive Hearing Preservation classification system presented in this paper is suitable for use for all cochlear implant users with measurable pre-operative residual hearing. If adopted as a universal reporting standard, as it was designed to be, it should prove highly beneficial by enabling future studies to quickly and easily compare the results of previous studies and meta-analyze their data. OBJECTIVES: To develop a comprehensive Hearing Preservation classification system suitable for use for all cochlear implant users with measurable pre-operative residual hearing. METHODS: The HEARRING group discussed and reviewed a number of different propositions of a HP classification systems and reviewed critical appraisals to develop a qualitative system in accordance with the prerequisites. RESULTS: The Hearing Preservation Classification System proposed herein fulfills the following necessary criteria: 1) classification is independent from users' initial hearing, 2) it is appropriate for all cochlear implant users with measurable pre-operative residual hearing, 3) it covers the whole range of pure tone average from 0 to 120 dB; 4) it is easy to use and easy to understand.

Development of an auditory implant manipulator for minimally invasive surgical insertion of implantable hearing devices.

OBJECTIVE: To present the auditory implant manipulator, a navigation-controlled mechanical and electronic system which enables minimally invasive ('keyhole') transmastoid access to the tympanic cavity. MATERIALS AND METHODS: The auditory implant manipulator is a miniaturised robotic system with five axes of movement and an integrated drill. It can be mounted on the operating table. We evaluated the surgical work field provided by the system, and the work sequence involved, using an anatomical whole head specimen. RESULTS: The work field provided by the auditory implant manipulator is considerably greater than required for conventional mastoidectomy. The work sequence for a keyhole procedure included pre-operative planning, arrangement of equipment, the procedure itself and post-operative analysis. CONCLUSION: Although system improvements are necessary, our preliminary results indicate that the auditory implant manipulator has the potential to perform keyhole insertion of implantable hearing devices.

[Verification of normative values for the Swiss version of the Freiburg speech intelligibility test]. / Uberprüfung der Bezugskurven der Schweizer Version des Freiburger Zahlen- und Einsilbertests.

BACKGROUND AND OBJECTIVE: In the Swiss version of the Freiburg speech intelligibility test five test words from the original German recording which are rarely used in Switzerland have been exchanged. Furthermore, differences in the transfer functions between headphone and loudspeaker presentation are not taken into account during calibration. New settings for the levels of the individual test words in the recommended recording and small changes in calibration procedures led us to make a verification of the currently used normative values. PATIENTS AND METHODS: Speech intelligibility was measured in 20 subjects with normal hearing using monosyllabic words and numbers via headphones and loudspeakers. RESULTS: On average, 50% speech intelligibility was reached at levels which were 7.5 dB lower under free-field conditions than for headphone presentation. The average difference between numbers and monosyllabic words was found to be 9.6 dB, which is considerably lower than the 14 dB of the current normative curves. CONCLUSIONS: There is a good agreement between our measurements and the normative values for tests using monosyllabic words and headphones, but not for numbers or free-field measurements.

Performance of an adaptive beamforming noise reduction scheme for hearing aid applications. I. Prediction of the signal-to-noise-ratio improvement.

Adaptive beamformers have been proposed as noise reduction schemes for conventional hearing aids and cochlear implants. A method to predict the amount of noise reduction that can be achieved by a two-microphone adaptive beamformer is presented. The prediction is based on a model of the acoustic environment in which the presence of one acoustic target-signal source and one acoustic noise source in a reverberant enclosure is assumed. The acoustic field is sampled using two omnidirectional microphones mounted close to the ears of a user. The model takes eleven different parameters into account, including reverberation time and size of the room, directionality of the acoustic sources, and design parameters of the beamformer itself, including length of the adaptive filter and delay in the target signal path. An approximation to predict the achievable signal-to-noise improvement based on the model is presented. Potential applications as well as limitations of the proposed prediction method are discussed and a FORTRAN subroutine to predict the achievable signal-to-noise improvement is provided. Experimental verification of the predictions is provided in a companion paper [J. Acoust. Soc. Am. 109, 1134 (2001)].