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1.  Cochlear Implantation in Adults with Asymmetric Hearing Loss 
Ear and Hearing  2012;33(4):521-533.
Objective
Bilateral severe-to-profound sensorineural hearing loss is a standard criterion for cochlear implantation. Increasingly, patients are implanted in one ear and continue to use a hearing aid in the non-implanted ear to improve abilities such as sound localization and speech understanding in noise. Patients with severe-to-profound hearing loss in one ear and a more moderate hearing loss in the other ear (i.e., asymmetric hearing) are not typically considered candidates for cochlear implantation. Amplification in the poorer ear is often unsuccessful due to limited benefit, restricting the patient to unilateral listening from the better ear alone. The purpose of this study was to determine if patients with asymmetric hearing loss could benefit from cochlear implantation in the poorer ear with continued use of a hearing aid in the better ear.
Design
Ten adults with asymmetric hearing between ears participated. In the poorer ear, all participants met cochlear implant candidacy guidelines; seven had postlingual onset and three had pre/perilingual onset of severe-to-profound hearing loss. All had open-set speech recognition in the better hearing ear. Assessment measures included word and sentence recognition in quiet, sentence recognition in fixed noise (four-talker babble) and in diffuse restaurant noise using an adaptive procedure, localization of word stimuli and a hearing handicap scale. Participants were evaluated pre-implant with hearing aids and post-implant with the implant alone, the hearing aid alone in the better ear and bimodally (the implant and hearing aid in combination). Postlingual participants were evaluated at six months post-implant and pre/perilingual participants were evaluated at six and 12 months post-implant. Data analysis compared results 1) of the poorer hearing ear pre-implant (with hearing aid) and post-implant (with cochlear implant), 2) with the device(s) used for everyday listening pre- and post-implant and, 3) between the hearing aid-alone and bimodal listening conditions post-implant.
Results
The postlingual participants showed significant improvements in speech recognition after six months cochlear implant use in the poorer ear. Five postlingual participants had a bimodal advantage over the hearing aid-alone condition on at least one test measure. On average, the postlingual participants had significantly improved localization with bimodal input compared to the hearing aid-alone. Only one pre/perilingual participant had open-set speech recognition with the cochlear implant. This participant had better hearing than the other two pre/perilingual participants in both the poorer and better ear. Localization abilities were not significantly different between the bimodal and hearing aid-alone conditions for the pre/perilingual participants. Mean hearing handicap ratings improved post-implant for all participants indicating perceived benefit in everyday life with the addition of the cochlear implant.
Conclusions
Patients with asymmetric hearing loss who are not typical cochlear implant candidates can benefit from using a cochlear implant in the poorer ear with continued use of a hearing aid in the better ear. For this group of ten, the seven postlingually deafened participants showed greater benefits with the cochlear implant than the pre/perilingual participants; however, further study is needed to determine maximum benefit for those with early onset of hearing loss.
doi:10.1097/AUD.0b013e31824b9dfc
PMCID: PMC3383437  PMID: 22441359
Asymmetric hearing loss; Bilateral; Bimodal; Cochlear implant; Speech recognition
2.  Bilateral Cochlear Implants in Children: Localization Acuity Measured with Minimum Audible Angle 
Ear and hearing  2006;27(1):43-59.
Objective
To evaluate sound localization acuity in a group of children who received bilateral (BI) cochlear implants in sequential procedures and to determine the extent to which BI auditory experience affects sound localization acuity. In addition, to investigate the extent to which a hearing aid in the nonimplanted ear can also provide benefits on this task.
Design
Two groups of children participated, 13 with BI cochlear implants (cochlear implant + cochlear implant), ranging in age from 3 to 16 yrs, and six with a hearing aid in the nonimplanted ear (cochlear implant + hearing aid), ages 4 to 14 yrs. Testing was conducted in large sound-treated booths with loudspeakers positioned on a horizontal arc with a radius of 1.5 m. Stimuli were spondaic words recorded with a male voice. Stimulus levels typically averaged 60 dB SPL and were randomly roved between 56 and 64 dB SPL (±4 dB rove); in a few instances, levels were held fixed (60 dB SPL). Testing was conducted by using a “listening game” platform via computerized interactive software, and the ability of each child to discriminate sounds presented to the right or left was measured for loudspeakers subtending various angular separations. Minimum audible angle thresholds were measured in the BI (cochlear implant + cochlear implant or cochlear implant + hearing aid) listening mode and under monaural conditions.
Results
Approximately 70% (9/13) of children in the cochlear implant + cochlear implant group discriminated left/right for source separations of ≤20° and, of those, 77% (7/9) performed better when listening bilaterally than with either cochlear implant alone. Several children were also able to perform the task when using a single cochlear implant, under some conditions. Minimum audible angle thresholds were better in the first cochlear implant than the second cochlear implant listening mode for nearly all (8/9) subjects. Repeated testing of a few individual subjects over a 2-yr period suggests that robust improvements in performance occurred with increased auditory experience. Children who wore hearing aids in the nonimplanted ear were at times also able to perform the task. Average group performance was worse than that of the children with BI cochlear implants when both ears were activated (cochlear implant + hearing aid versus cochlear implant + cochlear implant) but not significantly different when listening with a single cochlear implant.
Conclusions
Children with sequential BI cochlear implants represent a unique population of individuals who have undergone variable amounts of auditory deprivation in each ear. Our findings suggest that many but not all of these children perform better on measures of localization acuity with two cochlear implants compared with one and are better at the task than children using the cochlear implant + hearing aid. These results must be interpreted with caution, because benefits on other tasks as well as the long-term benefits of BI cochlear implants are yet to be fully understood. The factors that might contribute to such benefits must be carefully evaluated in large populations of children using a variety of measures.
doi:10.1097/01.aud.0000194515.28023.4b
PMCID: PMC2651156  PMID: 16446564
3.  Binaural Fusion and Listening Effort in Children Who Use Bilateral Cochlear Implants: A Psychoacoustic and Pupillometric Study 
PLoS ONE  2015;10(2):e0117611.
Bilateral cochlear implants aim to provide hearing to both ears for children who are deaf and promote binaural/spatial hearing. Benefits are limited by mismatched devices and unilaterally-driven development which could compromise the normal integration of left and right ear input. We thus asked whether children hear a fused image (ie. 1 vs 2 sounds) from their bilateral implants and if this “binaural fusion” reduces listening effort. Binaural fusion was assessed by asking 25 deaf children with cochlear implants and 24 peers with normal hearing whether they heard one or two sounds when listening to bilaterally presented acoustic click-trains/electric pulses (250 Hz trains of 36 ms presented at 1 Hz). Reaction times and pupillary changes were recorded simultaneously to measure listening effort. Bilaterally implanted children heard one image of bilateral input less frequently than normal hearing peers, particularly when intensity levels on each side were balanced. Binaural fusion declined as brainstem asymmetries increased and age at implantation decreased. Children implanted later had access to acoustic input prior to implantation due to progressive deterioration of hearing. Increases in both pupil diameter and reaction time occurred as perception of binaural fusion decreased. Results indicate that, without binaural level cues, children have difficulty fusing input from their bilateral implants to perceive one sound which costs them increased listening effort. Brainstem asymmetries exacerbate this issue. By contrast, later implantation, reflecting longer access to bilateral acoustic hearing, may have supported development of auditory pathways underlying binaural fusion. Improved integration of bilateral cochlear implant signals for children is required to improve their binaural hearing.
doi:10.1371/journal.pone.0117611
PMCID: PMC4323344  PMID: 25668423
4.  Simultaneous Bilateral Cochlear Implantation in Adults: A Multicenter Clinical Study 
Ear and hearing  2006;27(6):714-731.
Objective
To determine the efficacy of “simultaneous” bilateral cochlear implantation (both implants placed during a single surgical procedure) by comparing bilateral and unilateral implant use in a large number of adult subjects tested at multiple sites.
Design
Prospective study of 37 adults with postlinguistic onset of bilateral, severe to profound sensorineural hearing loss. Performance with the bilateral cochlear implants, using the same speech processor type and speech processing strategy, was compared with performance using the left implant alone and the right implant alone. Speech understanding in quiet (CNCs and HINT sentences) and in noise (BKB-SIN Test) were evaluated at several postactivation time intervals, with speech presented at 0° azimuth, and noise at either 0°, 90° right, or 90° left in the horizontal plane. APHAB questionnaire data were collected after each subject underwent a 3-wk “bilateral deprivation” period, during which they wore only the speech processor that produced the best score during unilateral testing, and also after a period of listening again with the bilateral implants.
Results
By 6-mo postactivation, a significant advantage for speech understanding in quiet was found in the bilateral listening mode compared with either unilateral listening modes. For speech understanding in noise, the largest and most robust bilateral benefit was when the subject was able to take advantage of the head shadow effect; i.e., results were significantly better for bilateral listening compared with the unilateral condition when the ear opposite to the side of the noise was added to create the bilateral condition. This bilateral benefit was seen on at least one of the two unilateral ear comparisons for nearly all (32/34) subjects. Bilateral benefit was also found for a few subjects in spatial configurations that evaluated binaural redundancy and binaural squelch effects. A subgroup of subjects who had asymmetrical unilateral implant performances were, overall, similar in performance to subjects with symmetrical hearing. The questionnaire data indicated that bilateral users perceive their own performance to be better with bilateral cochlear implants than when using a single device.
Conclusions
Findings with a large patient group are in agreement with previous reports on smaller groups, showing that, overall, bilateral implantation offers the majority of patients advantages when listening in simulated adverse conditions.
doi:10.1097/01.aud.0000246816.50820.42
PMCID: PMC2651401  PMID: 17086081
5.  Recognition and Localization of Speech by Adult Cochlear Implant Recipients Wearing a Digital Hearing Aid in the Nonimplanted Ear (Bimodal Hearing) 
Background
The use of bilateral amplification is now common clinical practice for hearing aid users but not for cochlear implant recipients. In the past, most cochlear implant recipients were implanted in one ear and wore only a monaural cochlear implant processor. There has been recent interest in benefits arising from bilateral stimulation that may be present for cochlear implant recipients. One option for bilateral stimulation is the use of a cochlear implant in one ear and a hearing aid in the opposite nonimplanted ear (bimodal hearing).
Purpose
This study evaluated the effect of wearing a cochlear implant in one ear and a digital hearing aid in the opposite ear on speech recognition and localization.
Research Design
A repeated-measures correlational study was completed.
Study Sample
Nineteen adult Cochlear Nucleus 24 implant recipients participated in the study.
Intervention
The participants were fit with a Widex Senso Vita 38 hearing aid to achieve maximum audibility and comfort within their dynamic range.
Data Collection and Analysis
Soundfield thresholds, loudness growth, speech recognition, localization, and subjective questionnaires were obtained six–eight weeks after the hearing aid fitting. Testing was completed in three conditions: hearing aid only, cochlear implant only, and cochlear implant and hearing aid (bimodal). All tests were repeated four weeks after the first test session. Repeated-measures analysis of variance was used to analyze the data. Significant effects were further examined using pairwise comparison of means or in the case of continuous moderators, regression analyses. The speech-recognition and localization tasks were unique, in that a speech stimulus presented from a variety of roaming azimuths (140 degree loudspeaker array) was used.
Results
Performance in the bimodal condition was significantly better for speech recognition and localization compared to the cochlear implant–only and hearing aid–only conditions. Performance was also different between these conditions when the location (i.e., side of the loudspeaker array that presented the word) was analyzed. In the bimodal condition, the speech-recognition and localization tasks were equal regardless of which side of the loudspeaker array presented the word, while performance was significantly poorer for the monaural conditions (hearing aid only and cochlear implant only) when the words were presented on the side with no stimulation. Binaural loudness summation of 1–3 dB was seen in soundfield thresholds and loudness growth in the bimodal condition. Measures of the audibility of sound with the hearing aid, including unaided thresholds, soundfield thresholds, and the Speech Intelligibility Index, were significant moderators of speech recognition and localization. Based on the questionnaire responses, participants showed a strong preference for bimodal stimulation.
Conclusions
These findings suggest that a well-fit digital hearing aid worn in conjunction with a cochlear implant is beneficial to speech recognition and localization. The dynamic test procedures used in this study illustrate the importance of bilateral hearing for locating, identifying, and switching attention between multiple speakers. It is recommended that unilateral cochlear implant recipients, with measurable unaided hearing thresholds, be fit with a hearing aid.
PMCID: PMC2876351  PMID: 19594084
Bimodal hearing; cochlear implant; hearing aid; localization; speech recognition
6.  Effects of unilateral input and mode of hearing in the better ear: Self-reported performance using the Speech, Spatial and Qualities of Hearing Scale 
Ear and hearing  2014;35(1):10.1097/AUD.0b013e3182a3648b.
Objective
To evaluate effects of hearing mode (normal hearing, cochlear implant or hearing aid) on everyday communication among adult unilateral listeners using the Speech, Spatial and Qualities of Hearing scale (SSQ). Individuals with one good, naturally hearing ear were expected to have higher overall ratings than unilateral listeners dependent on a cochlear implant or hearing aid. We anticipated that listening environments reliant on binaural processing for successful communication would be rated most disabling by all unilateral listeners. Regardless of hearing mode, all hearing-impaired participants were expected to have lower ratings than individuals with normal hearing bilaterally. A secondary objective was to compare post-treatment SSQ results of participants who subsequently obtained a cochlear implant for the poorer hearing ear to those of participants with a single normal hearing ear.
Design
Participants were 87 adults recruited as part of ongoing research investigating asymmetric hearing effects. Sixty-six participants were unilateral listeners who had one unaided/non-implanted severe to profound hearing loss ear and were grouped based on hearing mode of the better ear: 30 had one normal hearing ear (i.e., unilateral hearing loss participants); 20 had a unilateral cochlear implant; and 16 had a unilateral hearing aid. Data were also collected from 21 normal-hearing individuals, as well as a subset of participants who subsequently received a cochlear implant in the poorer ear and thus became bilateral listeners. Data analysis was completed at the domain and subscale levels.
Results
A significant mode-of-hearing group effect for the hearing-impaired participants (i.e. with unilateral hearing loss, unilateral cochlear implant or unilateral hearing aid) was identified for two domains (Speech and Qualities) and six subscales (Speech in Quiet, Speech in Noise, Speech in Speech Contexts, Multiple Speech Stream Processing and Switching, Identification of Sound and Objects, and Sound Quality and Naturalness). There was no significant mode-of-hearing group effect for the Spatial domain or the other four subscales (Localization, Distance and Movement, Segregation of Sounds, and Listening Effort). Follow-up analysis indicated the unilateral normal hearing ear group had significantly higher ratings than the unilateral cochlear implant and/or hearing aid groups for the Speech domain and four of the ten subscales; neither the cochlear implant nor hearing aid group had subscale ratings significantly higher than each other or the unilateral hearing loss group. Audibility and sound quality imparted by hearing mode were identified as factors related to subjective listening experience. After cochlear implantation to restore bilateral hearing, SSQ ratings for bilateral cochlear implant and/or cochlear implant plus hearing aid participants were significantly higher than those of the unilateral hearing loss group for Speech in Quiet, Speech in Noise, Localization, Distance and Movement, Listening Effort, and the Spatial domain. Hearing-impaired individuals had significantly poorer ratings in all areas compared to those with bilateral normal hearing.
Conclusions
Adults reliant on a single ear, irrespective of better ear hearing mode, including those with one normal hearing ear, are at a disadvantage in all aspects of everyday listening and communication. Audibility and hearing mode were shown to differentially contribute to listening experience.
doi:10.1097/AUD.0b013e3182a3648b
PMCID: PMC3872501  PMID: 24084062
Unilateral hearing loss; Hearing disability; Cochlear implant; Hearing aid
7.  Fully implantable Otologics MET Carina™ device for the treatment of sensorineural hearing loss. Preliminary surgical and clinical results 
Summary
Middle ear implants overcome some of the common problems of conventional hearing aid technology, such as feedback, signal distortion, ear canal occlusion and associated issues. The Otologics MET Carina™, Boulder, CO, USA, is a fully implantable hearing prosthesis designed to address the amplification needs of adults (> 18 years of age), with moderate to severe sensorineural hearing loss and normal middle ears, providing a mechanical direct stimulation of middle ear ossicles. Recently, it has been successfully used also in patients with conductive hearing loss. In the present report, personal surgical and clinical experience with the fully implantable Carina™ is described in 5 adults with moderate to severe sensorineural hearing loss, operated upon between November 2007 and May 2008 in the ENT Unit, University of Pisa. Mean follow-up was 10.2 months of device use (range 7-13). Surgery was performed under general anaesthesia, in ~3 hours, with no surgical complications in any of the patients. In these 5 cases, no significant post-operative variation was observed in hearing thresholds, either for air or bone conduction, indicating absence of surgical damage to the cochlea. All patients showed improvements in hearing thresholds, in free field and in speech perception abilities, with the device functioning, moreover, they reported subjective benefits. With regard to post-operative adverse effects, no cases of extrusion of the device, device failure, loss of external communication or increased charging times were observed. Problems of feedback noise occurred, which were resolved with minor fitting adjustments in 4 cases, while a second operation was required to change the microphone position in the other patient. The present results, in agreement with those reported in the literature, confirm that the Otologics MET Carina™ is viable treatment for moderate to severe sensorineural hearing loss and, in selected cases, may represent an alternative to conventional hearing aids.
PMCID: PMC2808684  PMID: 20111617
Sensorineural hearing loss; Middle ear implants
8.  Sequential Bilateral Cochlear Implantation in a Patient with Bilateral Meniere’s Disease 
This case study describes a 45 year old female with bilateral, profound sensorineural hearing loss due to Meniere’s disease. She received her first cochlear implant in the right ear in 2008 and the second cochlear implant in the left ear in 2010. The case study examines the enhancement to speech recognition, particularly in noise, provided by bilateral cochlear implants.
Speech recognition tests were administered prior to obtaining the second implant and at a number of test intervals following activation of the second device. Speech recognition in quiet and noise as well as localization abilities were assessed in several conditions to determine bilateral benefit and performance differences between ears. The results of the speech recognition testing indicated a substantial improvement in the patient’s ability to understand speech in noise and her ability to localize sound when using bilateral cochlear implants compared to using a unilateral implant or an implant and a hearing aid. In addition, the patient reported considerable improvement in her ability to communicate in daily life when using bilateral implants versus a unilateral implant.
This case suggests that cochlear implantation is a viable option for patients who have lost their hearing to Meniere’s disease even when a number of medical treatments and surgical interventions have been performed to control vertigo. In the case presented, bilateral cochlear implantation was necessary for this patient to communicate successfully at home and at work.
doi:10.3766/jaaa.23.4.4
PMCID: PMC3431798  PMID: 22463939
Cochlear implant; hearing aid; Meniere’s disease; sensorineural hearing loss; speech recognition; vertigo
9.  Spatial Hearing and Speech Intelligibility in Bilateral Cochlear Implant Users 
Ear and hearing  2009;30(4):419-431.
Objective
The abilities to localize sounds and segregate speech from interfering sounds in a complex auditory environment were studied in a group of adults who use bilateral cochlear implants. The first aim of the study was to investigate the change in speech intelligibility under bilateral and unilateral listening modes as a function of bilateral experience during the first 6 mo of activation. The second aim was to look at whether localization and speech intelligibility in the presence of interfering speech are correlated and if the relationship is specific to the bilateral listening mode. The third aim was to examine whether sound lateralization (right versus left) emerges before sound localization within a hemifield.
Design
Participants were 17 native English speaking adults with postlingual deafness. All subjects received the Nucleus 24 Contour implant in both ears, either during the same surgery or during two separate surgeries that were no more than 1 mo apart. Both devices for each subject were activated at the same time, regardless of surgical approach. Speech intelligibility was measured at 3 and 6 mo after activation. Target speech was presented at 0° in front. Testing was conducted in quiet and in the presence of four-talker babble. The babble was located on the right, on the left, or in front (colocated with the target). Sound localization abilities were measured at the 3 mo interval. All testing was conducted under three listening modes: left ear alone, right ear alone, or bilateral.
Results
On the speech-in-babble task, benefit of listening with two ears compared with one was greater when going from 3 to 6 mo of experience. This was evident when the target speech and interfering speech were spatially separated, but not when they were presented from the same location. At 3 mo postactivation of bilateral hearing, 82% of subjects demonstrated bilateral benefit when right/left discrimination was evaluated. In contrast, 47% of subjects showed a bilateral benefit when sound localization was evaluated, suggesting that directional hearing might emerge in a two-step process beginning with discrimination and converging on more fine-grained localization. The bilateral speech intelligibility scores were positively correlated with sound localization abilities, so that listeners who were better able to hear speech in babble were generally better able to identify source locations.
Conclusions
During the early stages of bilateral hearing through cochlear implants in postlingually deafened adults, there is an early emergence of spatial hearing skills. Although nearly all subjects can discriminate source locations to the right versus left, less than half are able to perform the more difficult task of identifying source locations in a multispeaker array. Benefits for speech intelligibility with one versus two implants improve with time, in particular when spatial cues are used to segregate speech and competing noise. Localization and speech-in-noise abilities in this group of patients are somewhat correlated.
doi:10.1097/AUD.0b013e3181a165be
PMCID: PMC2873678  PMID: 19455039
10.  A Tutorial on Implantable Hearing Amplification Options for Adults with Unilateral Microtia and Atresia 
BioMed Research International  2014;2014:703256.
Background. Patients with unilateral atresia and microtia encounter problems in sound localization and speech understanding in noise. Although there are four implantable hearing devices available, there is little discussion and evidence on the application of these devices on patients with unilateral atresia and microtia problems. Objective. This paper will review the details of these four implantable hearing devices for the treatment of unilateral atresia. They are percuteaneous osseointegrated bone anchored hearing aid, Vibrant Soundbridge middle ear implant, Bonebridge bone conduction system, and Carina fully implantable hearing device. Methods. Four implantable hearing devices were reviewed and compared. The clinical decision process that led to the recommendation of a device was illustrated by using a case study. Conclusions. The selection of appropriate implantable hearing devices should be based on various factors, including radiological findings and patient preferences, possible surgical complications, whether the device is Food and Drug Administration- (FDA-)/CE-approved, and the finances. To ensure the accurate evaluation of candidacy and outcomes, the evaluation methods should be adapted to suite the type of hearing device.
doi:10.1155/2014/703256
PMCID: PMC4060767  PMID: 24991564
11.  Perception of Binaural Cues Develops in Children Who Are Deaf through Bilateral Cochlear Implantation 
PLoS ONE  2014;9(12):e114841.
There are significant challenges to restoring binaural hearing to children who have been deaf from an early age. The uncoordinated and poor temporal information available from cochlear implants distorts perception of interaural timing differences normally important for sound localization and listening in noise. Moreover, binaural development can be compromised by bilateral and unilateral auditory deprivation. Here, we studied perception of both interaural level and timing differences in 79 children/adolescents using bilateral cochlear implants and 16 peers with normal hearing. They were asked on which side of their head they heard unilaterally or bilaterally presented click- or electrical pulse- trains. Interaural level cues were identified by most participants including adolescents with long periods of unilateral cochlear implant use and little bilateral implant experience. Interaural timing cues were not detected by new bilateral adolescent users, consistent with previous evidence. Evidence of binaural timing detection was, for the first time, found in children who had much longer implant experience but it was marked by poorer than normal sensitivity and abnormally strong dependence on current level differences between implants. In addition, children with prior unilateral implant use showed a higher proportion of responses to their first implanted sides than children implanted simultaneously. These data indicate that there are functional repercussions of developing binaural hearing through bilateral cochlear implants, particularly when provided sequentially; nonetheless, children have an opportunity to use these devices to hear better in noise and gain spatial hearing.
doi:10.1371/journal.pone.0114841
PMCID: PMC4273969  PMID: 25531107
12.  Temporal bone histopathology in a case of sensorineural hearing loss caused by superficial siderosis of the central nervous system and treated by cochlear implantation 
Objectives
To evaluate the histopathology of the temporal bones of a patient with documented superficial siderosis of the central nervous system who underwent right cochlear implantation six years before death.
Background
Superficial siderosis of the central nervous system is due to chronic or repeated subarachnoid hemorrhage and results in sensorineural deafness in 95% of affected individuals in addition to other neurologic findings. The deposition of hemosiderin in the meninges and around cranial nerves is thought to be causative. There have been no previous reports of temporal bone pathology in this disorder.
This 57 year old man developed progressive, bilateral hearing loss starting in his 30's with loss of pure tone thresholds and word recognition. He underwent a right cochlear implant at age 51 with full insertion of the device.
Methods
The temporal bones and brainstem were fixed in formalin and prepared for histologic study by standard techniques. Special stains, including Gomori stain for iron were performed on sections of the temporal bones and cochlear nucleus.
Results
There was severe bilateral degeneration of the organ of Corti, spiral ligament, stria vascularis, and spiral ganglion cells. Gomori stain revealed iron deposits within the spiral ligament, stria vascularis and in the subepithelial mesenchymal tissue of the maculae of the vestibular system. Evaluation of the cochlear nucleus revealed iron deposits within glial cells and larger cells, probably macrophages, near the CSF surface. On the right side, the track created by the cochlear implant entered the scala tympani and continued to mm17, as measured from the round window.
Discussion and Conclusions
This is the first known case of superficial siderosis with documented temporal bone histopathology. Hearing loss was likely caused by severe degeneration of spiral ganglion cells in both ears, despite the presence of remaining hair cells in the middle and apical turns. This was consistent with cochlear neuronal degeneration and retrograde degeneration of spiral ganglion cells within the inner ear, or alternatively, consistent with primary degeneration of hair cells and neural structures within the cochlea. Despite the presence of neural degeneration, the patient achieved a word recognition score of 28% six months following implantation.
doi:10.1097/MAO.0b013e31820e7195
PMCID: PMC3137803  PMID: 21758021
Superficial siderosis; histopathology; temporal bone; hearing loss; cochlear implantation
13.  Bone Anchored Hearing Aid 
Executive Summary
Objective
The objective of this health technology policy assessment was to determine the effectiveness and cost-effectiveness of bone-anchored hearing aid (BAHA) in improving the hearing of people with conduction or mixed hearing loss.
The Technology
The (BAHA) is a bone conduction hearing device that includes a titanium fixture permanently implanted into the mastoid bone of the skull and an external percutaneous sound processor. The sound processor is attached to the fixture by means of a skin penetrating abutment. Because the device bypasses the middle ear and directly stimulates the cochlea, it has been recommended for individuals with conduction hearing loss or discharging middle ear infection.
The titanium implant is expected to last a lifetime while the external sound processor is expected to last 5 years. The total initial device cost is approximately $5,300 and the external sound processor costs approximately $3,500.
Review of BAHA by the Medical Advisory Secretariat
The Medical Advisory Secretariat’s review is a descriptive synthesis of findings from 36 research articles published between January 1990 and May 2002.
Summary of Findings
No randomized controlled studies were found. The evidence was derived from level 4 case series with relative small sample sizes (ranging from 30-188). The majority of the studies have follow-up periods of eight years or longer. All except one study were based on monaural BAHA implant on the side with the best bone conduction threshold.
Safety
Level 4 evidence showed that BAHA has been be implanted safely in adults and children with success rates of 90% or higher in most studies. No mortality or life threatening morbidity has been reported. Revision rates for tissue reduction or resiting were generally under 10% for adults but have been reported to be as high as 25% in pediatric studies.
Adverse skin reaction around the skin penetration site was the most common complication reported. Most of these conditions were successfully treated with antibiotics, and only 1% to 2% required surgical revision. Less than 1% required removal of the fixture.
Other complications included failure to osseointegrate and loss of fixture and/or abutment due to trauma or infection.
Effectiveness
Studies showed that BAHAs were implanted in people who have conduction or mixed hearing loss, congenital atresia or suppurative otitis media who were not candidates for surgical repair, and who cannot use conventional bone conduction hearing aids. The need for BAHA is not age- related. Objective audiometric measures and subjective patient satisfaction surveys showed that BAHA significantly improved the unaided and aided free field and sound field thresholds as well as speech discrimination in quiet and in noise for former users of conventional bone conduction hearing aids. The outcomes were ambiguous for former users of air conduction hearing aids.
BAHA has been shown to reduce the frequency of ear infection and reduce the discharge particularly among patients with suppurative otitis media.
Patients have reported that BAHA improved their quality of life. Reported benefits were improved speech intelligibility, better sound comfort, less pressure on the head, less skin irritation, greater cosmetic acceptance and increase in confidence. Main reported shortcomings were wind noise, feedback and difficulty in using the telephone.
Experts and the BAHA manufacturer recommended that recipients of a BAHA implant be at least 5 years old. Challenges associated with the implantation of BAHA in pediatric patients include thin bone, soft bone, higher rates of fixture loss due to trauma, psychological problems, and higher revision rates due to rapid bone growth. The overall outcomes are comparable to adult BAHA. The benefits of pediatric BAHA (e.g. on speech development) appear to outweigh the disadvantages.
Screening according to strict eligibility criteria, preoperative counselling, close monitoring by a physician with BAHA expertise and on-going follow-up were identified as critical factors for long-term implant survival. Examples of eligibility criteria were provided.
Cost-effectiveness
No literature on cost-effectiveness of BAHA was found.
PMCID: PMC3387772  PMID: 23074440
14.  Middle Ear Implantable Hearing Devices: An Overview 
Trends in Amplification  2009;13(3):206-214.
Hearing loss affects approximately 30 million people in the United States. It has been estimated that only approximately 20% of people with hearing loss significant enough to warrant amplification actually seek assistance for amplification. A significant interest in middle ear implants has emerged over the years to facilitate patients who are noncompliant with conventional hearing aides, do not receive significant benefit from conventional aides, or are not candidates for cochlear implants. From the initial studies in the 1930s, the technology has greatly evolved over the years with a wide array of devices and mechanisms employed in the development of implantable middle ear hearing devices. Currently, these devices are generally available in two broad categories: partially or totally implantable using either piezoelectric or electromagnetic systems. The authors present an up-to-date overview of the major implantable middle ear devices. Although the current devices are largely in their infancy, indications for middle ear implants are ever evolving as promising studies show good results. The totally implantable devices provide the user freedom from the social and practical difficulties of using conventional amplification.
doi:10.1177/1084713809346262
PMCID: PMC4111438  PMID: 19762429
hearing loss; ear implants; conventional amplification
15.  Cochlear Implantation in Non-Traditional Candidates: Preliminary Results in Adolescents with Asymmetric Hearing Loss 
Objective
Traditionally, children are cochlear implant (CI) candidates if bilateral severe to profound hearing loss is present and amplification benefit is limited. The current study investigated abilities of adolescents with asymmetric hearing loss (one ear with severe to profound hearing loss and better hearing contralaterally), where the poorer ear received a CI and the better ear maintained amplification.
Study Design
Within-subject case study
Setting
Pediatric hospital, outpatient clinic
Patients
Participants were five adolescents who had not met traditional CI candidacy due to one better hearing ear, but did have one ear that met criteria and was implanted. All maintained hearing aid (HA) use in the contralateral ear. In the poorer ear pre-implant, three participants had used amplification and the other two had no HA experience.
Main Outcome Measure
Participants were assessed in three listening conditions: HA alone, CI alone, and both devices together (bimodal) for speech recognition in quiet and noise, and sound localization.
Results
Three participants had CI open-set speech recognition and significant bimodal improvement for speech recognition and localization compared with the HA or CI alone. Two participants had no CI speech recognition and limited bimodal improvement.
Conclusions
Some adolescents with asymmetric hearing loss who are not typical CI candidates can benefit from a CI in the poorer ear, compared to a HA in the better ear alone. Additional study is needed to determine outcomes for this population, especially those who have early onset profound hearing loss in one ear and limited HA experience.
doi:10.1097/MAO.0b013e31827850b8
PMCID: PMC3600103  PMID: 23222962
16.  Binaural-Bimodal Fitting or Bilateral Implantation for Managing Severe to Profound Deafness: A Review 
Trends in Amplification  2007;11(3):161-192.
There are now many recipients of unilateral cochlear implants who have usable residual hearing in the nonimplanted ear. To avoid auditory deprivation and to provide binaural hearing, a hearing aid or a second cochlear implant can be fitted to that ear. This article addresses the question of whether better binaural hearing can be achieved with binaural/bimodal fitting (combining a cochlear implant and a hearing aid in opposite ears) or bilateral implantation. In the first part of this article, the rationale for providing binaural hearing is examined. In the second part, the literature on the relative efficacy of binaural/bimodal fitting and bilateral implantation is reviewed. Most studies on comparing either mode of bilateral stimulation with unilateral implantation reported some binaural benefits in some test conditions on average but revealed that some individuals benefited, whereas others did not. There were no controlled comparisons between binaural/bimodal fitting and bilateral implantation and no evidence to support the efficacy of one mode over the other. In the third part of the article, a crossover trial of two adults who had binaural/bimodal fitting and who subsequently received a second implant is reported. The findings at 6 and 12 months after they received their second implant indicated that binaural function developed over time, and the extent of benefit depended on which abilities were assessed for the individual. In the fourth and final parts of the article, clinical issues relating to candidacy for binaural/bimodal fitting and strategies for bimodal fitting are discussed with implications for future research.
doi:10.1177/1084713807304357
PMCID: PMC4111363  PMID: 17709573
bimodal hearing; bilateral implantation; deafness
17.  Benefits of Localization and Speech Perception with Multiple Noise Sources in Listeners with a Short-electrode Cochlear Implant 
Background
Research suggests that for individuals with significant low-frequency hearing, implantation of a short-electrode cochlear implant may provide benefits of improved speech perception abilities. Because this strategy combines acoustic and electrical hearing within the same ear while at the same time preserving low-frequency residual acoustic hearing in both ears, localization abilities may also be improved. However, very little research has focused on the localization and spatial hearing abilities of users with a short-electrode cochlear implant.
Purpose
The purpose of this study was to evaluate localization abilities for listeners with a short-electrode cochlear implant who continue to wear hearing aids in both ears. A secondary purpose was to document speech perception abilities using a speech in noise test with spatially-separate noise sources.
Research Design
Eleven subjects that utilized a short-electrode cochlear implant and bilateral hearing aids were tested on localization and speech perception with multiple noise locations using an eight-loudspeaker array. Performance was assessed across four listening conditions using various combinations of cochlear implant and/or hearing aid use.
Results
Results for localization showed no significant difference between using bilateral hearing aids and bilateral hearing aids plus the cochlear implant. However, there was a significant difference between the bilateral hearing aid condition and the implant plus use of a contralateral hearing aid for all eleven subjects. Results for speech perception showed a significant benefit when using bilateral hearing aids plus the cochlear implant over use of the implant plus only one hearing aid.
Conclusion
Combined use of both hearing aids and the cochlear implant show significant benefits for both localization and speech perception in noise for users with a short-electrode cochlear implant. These results emphasize the importance of low-frequency information in two ears for the purpose of localization and speech perception in noise.
PMCID: PMC2809934  PMID: 20085199
short-electrode; hybrid cochlear implant; cochlear implant and hearing aid; localization; speech perception
18.  Probe Microphone Measurements: 20 Years of Progress 
Trends in Amplification  2001;5(2):35-68.
Probe-microphone testing was conducted in the laboratory as early as the 1940s (e.g., the classic work of Wiener and Ross, reported in 1946), however, it was not until the late 1970s that a “dispenser friendly” system was available for testing hearing aids in the real ear. In this case, the term “dispenser friendly,” is used somewhat loosely. The 1970s equipment that I'm referring to was first described in a paper that was presented by Earl Harford, Ph.D. in September of 1979 at the International Ear Clinics' Symposium in Minneapolis. At this meeting, Earl reported on his clinical experiences of testing hearing aids in the real ear using a miniature (by 1979 standards) Knowles microphone. The microphone was coupled to an interfacing impedance matching system (developed by David Preves, Ph.D., who at the time worked at Starkey Laboratories) which could be used with existing hearing aid analyzer systems (see Harford, 1980 for review of this early work). Unlike today's probe tube microphone systems, this early method of clinical real-ear measurement involved putting the entire microphone (about 4mm by 5mm by 2mm) in the ear canal down by the eardrum of the patient. If you think cerumen is a problem with probe-mic measurements today, you should have seen the condition of this microphone after a day's work!
While this early instrumentation was a bit cumbersome, we quickly learned the advantages that probe-microphone measures provided in the fitting of hearing aids. We frequently ran into calibration and equalization problems, not to mention a yelp or two from the patient, but the resulting information was worth the trouble.
Help soon arrived. In the early 1980s, the first computerized probe-tube microphone system, the Rastronics CCI-10 (developed in Denmark by Steen Rasmussen), entered the U.S. market (Nielsen and Rasmussen, 1984). This system had a silicone tube attached to the microphone (the transmission of sound through this tube was part of the calibration process), which eliminated the need to place the microphone itself in the ear canal. By early 1985, three or four different manufactures had introduced this new type of computerized probe-microphone equipment, and this hearing aid verification procedure became part of the standard protocol for many audiology clinics. At his time, the POGO (Prescription Of Gain and Output) and Libby 1/3 prescriptive fitting methods were at the peak of their popularity, and a revised NAL (National Acoustic Laboratories) procedure was just being introduced. All three of these methods were based on functional gain, but insertion gain easily could be substituted, and therefore, manufacturers included calculation of these prescriptive targets as part of the probe-microphone equipment software. Audiologists, frustrated with the tedious and unreliable functional gain procedure they had been using, soon developed a fascination with matching real-ear results to prescriptive targets on a computer monitor.
In some ways, not a lot has changed since those early days of probe-microphone measurements. Most people who use this equipment simply run a gain curve for a couple inputs and see if it's close to prescriptive target—something that could be accomplished using the equipment from 1985. Contrary to the predictions of many, probe-mic measures have not become the “standard hearing aid verification procedure.” (Mueller and Strouse, 1995). There also has been little or no increase in the use of this equipment in recent years. In 1998, I reported on a survey that was conducted by The Hearing Journal regarding the use of probe-microphone measures (Mueller, 1998). We first looked at what percent of people dispensing hearing aids own (or have immediate access to) probe-microphone equipment. Our results showed that 23% of hearing instrument specialists and 75% of audiologists have this equipment. Among audiologists, ownership varied among work settings: 91% for hospitals/clinics, 73% for audiologists working for physicians, and 69% for audiologists in private practice. But more importantly, and a bit puzzling, was the finding that showed that nearly one half of the people who fit hearing aids and have access to this equipment, seldom or never use it.
I doubt that the use rate of probe-microphone equipment has changed much in the last three years, and if anything, I suspect it has gone down. Why do I say that? As programmable hearing aids have become the standard fitting in many clinics, it is tempting to become enamoured with the simulated gain curves on the fitting screen, somehow believing that this is what really is happening in the real ear. Additionally, some dispensers have been told that you can't do reliable probe-mic testing with modern hearing aids—this of course is not true, and we'll address this issue in the Frequently Asked Questions portion of this paper.
The infrequent use of probe-mic testing among dispensers is discouraging, and let's hope that probe-mic equipment does not suffer the fate of the rowing machine stored in your garage. A lot has changed over the years with the equipment itself, and there are also expanded clinical applications and procedures. We have new manufacturers, procedures, acronyms and noises. We have test procedures that allow us to accurately predict the output of a hearing aid in an infant's ear. We now have digital hearing aids, which provide us the opportunity to conduct real-ear measures of the effects of digital noise reduction, speech enhancement, adaptive feedback, expansion, and all the other features. Directional microphone hearing aids have grown in popularity and what better way to assess the real-ear directivity than with probe-mic measures? The array of assistive listening devices has expanded, and so has the role of the real-ear assessment of these products. And finally, with today's PC -based systems, we can program our hearing aids and simultaneously observe the resulting real-ear effects on the same fitting screen, or even conduct an automated target fitting using earcanal monitoring of the output. There have been a lot of changes, and we'll talk about all of them in this issue of Trends.
doi:10.1177/108471380100500202
PMCID: PMC4168927  PMID: 25425897
19.  Pediatric cochlear implantation: an update 
Deafness in pediatric age can adversely impact language acquisition as well as educational and social-emotional development. Once diagnosed, hearing loss should be rehabilitated early; the goal is to provide the child with maximum access to the acoustic features of speech within a listening range that is safe and comfortable. In presence of severe to profound deafness, benefit from auditory amplification cannot be enough to allow a proper language development. Cochlear implants are partially implantable electronic devices designed to provide profoundly deafened patients with hearing sensitivity within the speech range. Since their introduction more than 30 years ago, cochlear implants have improved their performance to the extent that are now considered to be standard of care in the treatment of children with severe to profound deafness. Over the years patient candidacy has been expanded and the criteria for implantation continue to evolve within the paediatric population. The minimum age for implantation has progressively reduced; it has been recognized that implantation at a very early age (12–18 months) provides children with the best outcomes, taking advantage of sensitive periods of auditory development. Bilateral implantation offers a better sound localization, as well as a superior ability to understand speech in noisy environments than unilateral cochlear implant. Deafened children with special clinical situations, including inner ear malformation, cochlear nerve deficiency, cochlear ossification, and additional disabilities can be successfully treated, even thogh they require an individualized candidacy evaluation and a complex post-implantation rehabilitation. Benefits from cochlear implantation include not only better abilities to hear and to develop speech and language skills, but also improved academic attainment, improved quality of life, and better employment status. Cochlear implants permit deaf people to hear, but they have a long way to go before their performance being comparable to that of the intact human ear; researchers are looking for more sophisticated speech processing strategies as well as a more efficient coupling between the electrodes and the cochlear nerve with the goal of dramatically improving the quality of sound of the next generation of implants.
doi:10.1186/s13052-014-0072-8
PMCID: PMC4282008  PMID: 25179127
Sensorineural hearing loss; Cochlear implantation; Hearing rehabilitation; Surgery
20.  Examination of a Mechanical Amplifier in the Incudostapedial Joint Gap: FEM Simulation and Physical Model 
Sensors (Basel, Switzerland)  2014;14(8):14356-14374.
Implantable assembly components that are biocompatible and highly miniaturized are an important objective for hearing aid development. We introduce a mechanical transducer, which could be suitable as part of a prospective fully-implantable hearing aid. The transducer comprises a sensor and an actuator unit in one housing, located in the joint gap between the middle ear ossicles, the incus and stapes. The setup offers the advantage of a minimally invasive and reversible surgical solution. However, feedback between actuator and sensor due to mechanical coupling limits the available stable gain. We show that the system can be stabilized by digital control algorithms. The transducer is tested both in a finite elements method simulation of the middle ear and a physical model of a human middle ear. First, we characterize the sensor and actuator elements separately. Then, the maximum stable gain (MSG) of the whole transducer is experimentally determined in the middle ear model. With digital feedback control (using a least mean squares algorithm) in place, the total signal gain is greater than 30 dB for frequencies of 1 kHz and above. This shows the potential of the transducer as a high frequency hearing aid.
doi:10.3390/s140814356
PMCID: PMC4178999  PMID: 25106020
fully implantable; membrane transducer; ossicular chain; middle ear; hearing aid; FEM; feedback suppression
21.  Two Ears and Two (or More?) Devices: A Pediatric Case Study of Bilateral Profound Hearing Loss 
Trends in Amplification  2009;13(2):107-123.
Advances in technology and expanding candidacy guidelines have motivated many clinics to consider children with precipitously sloping high-frequency hearing loss as candidates for cochlear implants (CIs). A case study is presented of a pediatric CI patient whose hearing thresholds were preserved within 10 dB of preimplant levels (125–750 Hz) after receiving a fully inserted 31.5-mm electrode array at one ear. The primary goal of this study was to explore the possible benefit of using both a hearing aid (HA) and a CI at one ear while using a HA at the opposite ear. The authors find that although the use of bilateral hearing aids with a CI may only provide a slight benefit, careful attention must be paid to the coordinated fitting of devices, especially at the ear with two devices.
doi:10.1177/1084713809336423
PMCID: PMC4111527  PMID: 19447765
bimodal; electroacoustic; pediatric; cochlear implant
22.  Music Perception with Cochlear Implants: A Review 
Trends in Amplification  2004;8(2):49-82.
The acceptance of cochlear implantation as an effective and safe treatment for deafness has increased steadily over the past quarter century. The earliest devices were the first implanted prostheses found to be successful in compensating partially for lost sensory function by direct electrical stimulation of nerves. Initially, the main intention was to provide limited auditory sensations to people with profound or total sensorineural hearing impairment in both ears. Although the first cochlear implants aimed to provide patients with little more than awareness of environmental sounds and some cues to assist visual speech-reading, the technology has advanced rapidly. Currently, most people with modern cochlear implant systems can understand speech using the device alone, at least in favorable listening conditions. In recent years, an increasing research effort has been directed towards implant users’ perception of nonspeech sounds, especially music. This paper reviews that research, discusses the published experimental results in terms of both psychophysical observations and device function, and concludes with some practical suggestions about how perception of music might be enhanced for implant recipients in the future. The most significant findings of past research are: (1) On average, implant users perceive rhythm about as well as listeners with normal hearing; (2) Even with technically sophisticated multiple-channel sound processors, recognition of melodies, especially without rhythmic or verbal cues, is poor, with performance at little better than chance levels for many implant users; (3) Perception of timbre, which is usually evaluated by experimental procedures that require subjects to identify musical instrument sounds, is generally unsatisfactory; (4) Implant users tend to rate the quality of musical sounds as less pleasant than listeners with normal hearing; (5) Auditory training programs that have been devised specifically to provide implant users with structured musical listening experience may improve the subjective acceptability of music that is heard through a prosthesis; (6) Pitch perception might be improved by designing innovative sound processors that use both temporal and spatial patterns of electric stimulation more effectively and precisely to overcome the inherent limitations of signal coding in existing implant systems; (7) For the growing population of implant recipients who have usable acoustic hearing, at least for low-frequency sounds, perception of music is likely to be much better with combined acoustic and electric stimulation than is typical for deaf people who rely solely on the hearing provided by their prostheses.
doi:10.1177/108471380400800203
PMCID: PMC4111359  PMID: 15497033
23.  New Criteria of Indication and Selection of Patients to Cochlear Implant 
Numerous changes continue to occur in cochlear implant candidacy. In general, these have been accompanied by concomitant and satisfactory changes in surgical techniques. Together, this has advanced the utility and safety of cochlear implantation. Most devices are now approved for use in patients with severe to profound unilateral hearing loss rather then the prior requirement of a bilateral profound loss. Furthermore, studies have begun utilizing short electrode arrays for shallow insertion in patients with considerable low-frequency residual hearing. This technique will allow the recipient to continue to use acoustically amplified hearing for the low frequencies simultaneously with a cochlear implant for the high frequencies. The advances in design of, and indications for, cochlear implants have been matched by improvements in surgical techniques and decrease in complications. The resulting improvements in safety and efficacy have further encouraged the use of these devices. This paper will review the new concepts in the candidacy of cochlear implant. Medline data base was used to search articles dealing with the following topics: cochlear implant in younger children, cochlear implant and hearing preservation, cochlear implant for unilateral deafness and tinnitus, genetic hearing loss and cochlear implant, bilateral cochlear implant, neuropathy and cochlear implant and neural plasticity, and the selection of patients for cochlear implant.
doi:10.1155/2011/573968
PMCID: PMC3195958  PMID: 22013448
24.  Younger- and older-age adults with unilateral and bilateral cochlear implants: Speech and spatial hearing self-ratings and performance 
Objective
Compare results of cochlear implantation in younger and older adults in the domains of disability and handicap, as well as in tests of word recognition and localization, across unilateral implant (CI), bilateral (CI+CI) and CI with an acoustic hearing aid in the non-implanted ear (CI+HA).
Design
Three parts: retrospective (post-implant only) analysis; prospective (pre-versus post-implant); correlation between age and benefit from CI versus CI+CI. Two age groups, above and below 60 years, for the first two analyses; age is a continuous variable for the third analysis.
Setting
Tertiary referral hospital clinic
Patients
Postlingually severely-to-profoundly hearing impaired adults: Totals of 68 CI, 36 CI+CI, and 38 CI+HA in the retrospective part of the study; totals of 30 CI, 18 CI+CI and 16 CI+HA in the prospective parts. Numbers vary from these totals on individual measures.
Interventions
Patients receive either one or two cochlear implants; some with one CI opt to retain a hearing aid in the non-implanted ear.
Outcome measures
Principal measures: Hearing Handicap Inventory for the Elderly, Hearing Handicap Questionnaire, Speech, Spatial and Qualities of Hearing scale, word recognition test, and soundfield localization test. The study is exploratory, but proceeding from a null hypothesis of no expected contrast as a function of patient age.
Results
All patient groups show significant benefit following implantation. No significant age-related differences are observed in patients with unilateral implant, nor in CI+HA group. In the CI+CI group, the younger cohort showed very substantial increases in both performance and self-rated abilities; the older cohort provides more mixed outcomes.
Conclusion
Results for the CI group confirm and extend earlier research. The result for the younger group of CI+CI patients demonstrates the consistent incremental benefit obtained from a bilateral procedure. The mixed outcome observed in the older CI+CI group might be due to individual differences in interaction between effects of aging and the ability to integrate binaural cues.
doi:10.1097/MAO.0b013e3181b76b3b
PMCID: PMC2828521  PMID: 19692936
25.  Testing a Method for Quantifying the Output of Implantable Middle Ear Hearing Devices 
Audiology & neuro-otology  2007;12(4):265-276.
This report describes tests of a standard practice for quantifying the performance of implantable middle ear hearing devices (also known as implantable hearing aids). The standard and these tests were initiated by the Food and Drug Administration of the United States Government. The tests involved measurements on two hearing devices, one commercially available and the other home built, that were implanted into ears removed from human cadavers. The tests were conducted to investigate the utility of the practice and its outcome measures: the equivalent ear canal sound pressure transfer function that relates electrically driven middle ear velocities to the equivalent sound pressure needed to produce those velocities, and the maximum effective ear canal sound pressure. The practice calls for measurements in cadaveric ears in order to account for the varied anatomy and function of different human middle ears.
doi:10.1159/000101474
PMCID: PMC2596735  PMID: 17406105
Implantable hearing aids; Middle ear transfer function; Sound-induced stapes velocity

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