Frequency discrimination with sequential or simultaneous stimulation in MED-EL cochlear implants

CONCLUSION: Amplitude weighting using the bell-shaped filter design within the OPUS speech processors allows the creation of pitches intermediate to those of two adjacent electrodes. This mechanism can be used for both sequential and simultaneous stimulation. OBJECTIVES: This paper describes frequency discrimination experiments which are based on amplitude weighting of two adjacent electrodes. The effects of sequential versus simultaneous stimulation of the electrode pair were investigated. MATERIALS AND METHODS: The experiment was performed using a laboratory system emulating the signal processing using bell-shaped filters in the MED-EL speech processors. The system transformed input files (wav-files) into the stimulation data stream which was transmitted to the implant via the OPUS processor coil. Pitch discrimination was assessed for up to three electrode pairs in each subject, using an adaptive test method. Results for sequential stimulation were collected in eight subjects, a comparison between sequential and simultaneous stimulation was made in five subjects. RESULTS: Results show an average frequency discrimination of 8.8% for sequential stimulation and 11.2% for simultaneous stimulation, of the nominal test frequency. Frequency discrimination ability varied across subjects and test electrode pairs. The difference in performance between sequential and simultaneous stimulation was not statistically significant.     

Trends in cochlear implants

More than 60,000 people worldwide use cochlear implants as a means to restore functional hearing. Although individual performance variability is still high, an average implant user can talk on the phone in a quiet environment. Cochlear-implant research has also matured as a field, as evidenced by the exponential growth in both the patient population and scientific publication. The present report examines current issues related to audiologic, clinical, engineering, anatomic, and physiologic aspects of cochlear implants, focusing on their psychophysical, speech, music, and cognitive performance. This report also forecasts clinical and research trends related to presurgical evaluation, fitting protocols, signal processing, and postsurgical rehabilitation in cochlear implants. Finally, a future landscape in amplification is presented that requires a unique, yet complementary, contribution from hearing aids, middle ear implants, and cochlear implants to achieve a total solution to the entire spectrum of hearing loss treatment and management.     

Pediatric cochlear implants

Cochlear implants are a safe and effective treatment for children with severe to profound sensorineural hearing loss. As implant technology continues to improve and outcomes are analyzed, younger and younger children are being deemed candidates for implantation. The decision to operate is made after a thorough evaluation by a multidisciplinary team. This review will highlight the preoperative and postoperative issues related to pediatric cochlear implantation.     

Surgical techniques in cochlear implants

Cochlear implants have a remarkable history and a promising future. As the cochlear implant has evolved, so has the surgical technique. This review encompasses a history of the cochlear implant, a summary of the evolution of the implant incision and the methods used to secure the device and the electrode, the cochleostomy versus round window debate, and a discussion of the validity of intraoperative tests. Advanced technology, new surgical techniques, and refining established techniques are hallmarks of cochlear implant surgery. Advancements, including image-guided surgery, hearing preservation with full insertion, and telemetry-based advanced programming, are expected to be standard in the future.     

Radiology for cochlear implants

One fifth of patients selected for cochlear implants have such bony irregularities in the cochlear duct that full insertion of a multichannel electrode array is impossible. Three cases of cochlear deafness are presented where pre- and post-operative radiology played an important part in the management. Standard CT at 2 mm cuts is compared with ultra high resolution CT at 1 mm cuts. The pitfall of poor definition is that the inexperienced surgeon may find himself unexpectedly drilling out an obliterated cochlear duct. Sections 30 degrees caudal to Reid's infra orbito-meatal base line at 1 mm intervals give maximum information for minimum radiation. Plain films show the placement of individual platinum electrode contacts in relation to the spiral 'frequency map' of the cochlea. This is vital information for the audiologist who has to route specific frequencies to specific sites within the ear for a good hearing result.     

Tinnitus and cochlear implants

Objective

Several published studies seem to confirm the clinical observation that cochlear implants (CI) have a suppressive effect on tinnitus in most CI users. The aim of this paper is to present our personal experiences on tinnitus improvement after cochlear implantation.

Methods

Before surgery, 51 post-lingually profoundly deaf adults, who underwent cochlear implantation between 2005 and 2007, filled out a questionnaire reporting tinnitus characteristics and the Italian version of the Tinnitus Handicap Inventory (THI-I). Moreover, they were asked to scale tinnitus loudness and annoyance. Six months after implant activation, patients repeated the same evaluations. Scores were statistically analysed by means of a Wilcoxon signed ranks test on the hypothesis that a CI could change the tinnitus magnitude and/or its annoyance.

Results

In our series of 36 patients, 36.10% reported total loudness suppression and another 41.6% reported a reduction. Annoyance scores reduced in 75% of patients. THI reduced in 72.2% of patients.

Conclusion

Tinnitus reduction after CI may manifest as several mechanisms, such as habituation, acoustic masking, direct electrical nerve stimulation and cortical reorganization. Nevertheless, it is our opinion that data on CI benefits on tinnitus should be interpreted with caution and it seems reasonable to admit that further data is still necessary before considering CI as a treatment of tinnitus especially in unilateral deafness.     

Binaural cochlear implants.

With the success of monaural cochlear implantation, patients frequently ask about having a second implant. We have performed binaural cochlear implants in 12 adult patients. Desire not to disrupt a functioning implant was the primary consideration in implanting the contralateral ear. Seven patients received a second 3M/House single-channel implant to upgrade to a magnetic external receiver. Four patients with a 3M/House device in one ear elected to place a Nucleus multichannel implant in the opposite ear. One patient with a poorly functioning Nucleus device elected to have a second Nucleus device. Four patients with a Nucleus and a 3M/House implant, one with binaural 3M/House implants, and one with binaural Nucleus implants were tested for auditory discrimination in order to quantify monaural versus binaural differences. The functional benefit of the second implant was mixed, but all patients showed some degree of objective improvement on one or more tests. Five of the six are regular users of both devices; the patient with binaural Nucleus implants wears only one. Despite the differing processing schemes, patients with a Nucleus device in one ear and a 3M/House device in the other ear are able to combine the two signals to advantage. We feel that cochlear implantation in the contralateral ear is an acceptable option in selected patients desiring an upgraded implant without placing a functioning implant at risk.     

Histopathology of cochlear implants in humans

The insertion of an intrascalar electrode array during cochlear implantation causes immediate damage to the inner ear and may result in delayed onset of additional damage that may interfere with neuronal stimulation. To date, there have been reports on fewer than 50 temporal bone specimens from patients who had undergone implantation during life. The majority of these were single-channel implants, whereas the majority of implants inserted today are multichannel systems. This report presents the histopathologic findings in temporal bones from 8 individuals who in life had undergone multichannel cochlear implantation, with particular attention to the type and location of trauma and to long-term changes within the cochlea. The effect of these changes on spiral ganglion cell counts and the correlation between speech comprehension and spiral ganglion cell counts were calculated. In 4 of the 8 cases, the opposite, unimplanted ear was available for comparison. In 3 of the 4 cases, there was no significant difference between the spiral ganglion cell counts on the implanted and unimplanted sides. In addition, in this series of 8 cases, there was an apparent negative correlation between residual spiral ganglion cell count and hearing performance during life as measured by single-syllable word recognition. This finding suggests that abnormalities in the central auditory pathways are at least as important as spiral ganglion cell loss in limiting the performance of implant users.     

Bioethical issues in pediatric cochlear implants

The use of cochlear implants can modify significantly the way in which deaf children relate with the outside world through psychological, linguistic and cognitive changes. The main question about this subject is the ethical controversy with regards to who has the right to make such a decision for a young child. We present the children evaluated at our hospital in order to assess the cochlear implant option. That population was of 37 implanted children, 10 children waiting for surgery and 21 rejected children. We describe and analyze from the bioethical bases and methodology the problems found: decision of no implant in children of hearing parents, the deaf culture point of view, the mature minor doctrine, teenagers, social and cultural problems, multihandicapped children and responsibility of the implants team.     

Infectious complications in pediatric cochlear implants

OBJECTIVES: Infectious complications may cause significant delay in cochlear implant device initiation and programming and be a source of additional morbidity. We reviewed our experience with infectious complications in the pediatric age group to determine specific sources that may not be seen in adults. STUDY DESIGN: A retrospective analysis from a single implant center. METHODS: Cases of pediatric cochlear implants were reviewed for data on infectious complications. Complications were identified as "major" or "minor," "early" or "delayed." Information was gathered regarding any comorbid, chronic health condition. Data related to the causative organism(s) were collected. RESULTS: Two hundred sixty-eight cases of pediatric implants were reviewed. Twenty-two cases were identified (an infection rate of 8.2%), all classified as "major." The majority, 12, were classified as "delayed" complications. Twenty-one cases required explantation with 14 successfully reimplanted. Five cases (in 4 patients) or 23% were associated with a specific chronic pediatric condition including two children with tracheostomies. Among implanted children who had chronic health conditions, 42% developed implant-related infections. Among otherwise healthy implanted children, only 6.6% developed implant-related infections. Resistant bacterial infections were not identified. CONCLUSIONS: Health conditions in the pediatric age group were associated with 23% of our complications, a risk factor not previously identified in the literature. These children, demonstrating seven times the infection rate of healthy children, should be carefully observed postoperatively. Overall, cochlear implantation in children continues to be associated with a low risk of infectious complications.     

Optimizing frequency-to-electrode allocation in cochlear implants

This study tested the hypothesis that speech perception of cochlear implant users could be improved by increasing the number of electrodes allocated to frequencies below 2.6 kHz, with correspondingly fewer electrodes allocated above this point. Eight users of the Nucleus CI22 implant participated and wore experimental maps in which the widths of the analysis filters were altered to provide either two or three extra low-frequency channels. Speech perception was tested following periods of take-home experience. Information transmission analysis of vowel and consonant confusions appear to support our hypothesis, showing that vowel first formant information was significantly better perceived with the experimental map and that consonant information was not significantly different. The results of CNC word testing appear to contradict this result, showing that the experimental map degraded both vowel and consonant perception. Overall, the experimental map had a small and variable effect on speech perception. These results do not support our hypothesis and indicate that further research is needed to investigate the possible effects of narrowing the filter bandwidth in low frequencies, as done in this experiment.     

Audiologists' attitudes to cochlear implants

215 audiologists completed a cross-sectional survey concerning attitudes towards cochlear implants and associated referral behaviours. Audiologists were found to hold positive attitudes towards cochlear implants, with the majority (65%) having referred at least one client for an assessment. Audiologists reported that the implant was a safe and effective technology and that they were satisfied with the progress made by clients with the device. Nonetheless, 84% of audiologists expressed concern about the psychosocial needs of clients within the implant programme. Referral behaviours were primarily associated with knowledge on how and when to refer a person for an assessment. Secondary factors included funding awareness, professional experience and training, and knowledge of, confidence in, and relationship to, a local implant programme. Referrals to implant clinics may be enhanced by fostering relationships within the broader audiological community.     

Tinnitus suppression by cochlear implants

The beneficial effects of cochlear implants on tinnitus have been noted in several studies, but few detailed appraisals of the phenomenon have been made. Six patients fitted with the UCSF/Storz cochlear implant device were studied. The effects of use of the implant device on tinnitus were monitored, and suppression of tinnitus was tracked throughout periods of stimulation and poststimulation. Tinnitus was effectively suppressed in five of six patients with the device on and with noise input, and reduction of perceived tinnitus loudness occurred in four of six with the device on but without acoustic input to the speech processor. Unilateral stimulation frequently resulted in bilateral tinnitus suppression. These studies reveal that profound tinnitus suppression is obtained by patients using their cochlear implants. Further work is required to quantify the optimal mode of stimulation, but these findings suggest that tinnitus sufferers may ultimately benefit from development of electrical stimulation tinnitus suppression devices.     

Audiologists' attitudes to cochlear implants

Abstract

215 audiologists completed a cross-sectional survey concerning attitudes towards cochlear implants and associated referral behaviours. Audiologists were found to hold positive attitudes towards cochlear implants, with the majority (65%) having referred at least one client for an assessment. Audiologists reported that the implant was a safe and effective technology and that they were satisfied with the progress made by clients with the device. Nonetheless, 84% of audiologists expressed concern about the psychosocial needs of clients within the implant programme. Referral behaviours were primarily associated with knowledge on how and when to refer a person for an assessment. Secondary factors included funding awareness, professional experience and training, and knowledge of, confidence in, and relationship to, a local implant programme. Referrals to implant clinics may be enhanced by fostering relationships within the broader audiological community.     

How cochlear implants encode speech

PURPOSE OF REVIEW: This review summarizes the history of cochlear implant signal processing and provides the rationale underlying current approaches. Present strategies are explained and recent research findings are summarized. It is suggested how these results may drive future advancements in signal processing. RECENT FINDINGS: Substantial advances have been made in our understanding of the spectral and temporal cues necessary for cochlear implant recipients to perceive music, speech in noise, and interaural timing. It is clear that higher levels of both spectral and temporal resolution, as well as better loudness and pitch coding are necessary for higher levels of performance. These factors are highly interrelated, however, and are beneficial for differing aspects of hearing. Signal processing algorithms incorporating these findings are under active development and some are currently undergoing clinical investigation. SUMMARY: Current implant devices, and those soon to be available, have substantial untapped potential to improve the auditory experience of their recipients. It is likely that in the near future, recent findings on pitch and loudness perception, as well as techniques to better emulate the normal functions of the cochlea will result in much higher levels of prosthetic hearing fidelity than are possible today. As the performance of these remarkable devices continues to improve, the population of hearing-impaired individuals who can benefit from implantation is likely to increase significantly.     

Sound code for cochlear implants

This is a review of how various commercially available cochlear prostheses encode speech and complex tones. Arguments in favor of temporal coding through relatively few channels are presented. Advantages of analogue over pulsatile stimuli are explained. Parameters responsible for perception of vowels, consonants, musical pitch and loudness are didactically analyzed. Active rehabilitation is considered an integral part of the coding effort.