Diameter of the cochlear nerve in deaf humans: implications for cochlear implantation.

Although the parameters that are most important for postoperative speech perception in cochlear implantation have not been identified, it is assumed that the numbers of remaining cochlear neurons and spiral ganglion cells in the implanted deaf ears are critical. In this study, we evaluated the correlation of the maximum diameter of the cochlear and vestibular nerve trunks with the number of spiral ganglion cells in horizontal sections of the temporal bone of 42 patients who were profoundly deaf during life, and in 5 patients with normal hearing. The maximum diameters of the cochlear, vestibular, and eighth cranial nerves were significantly smaller in the deaf population as compared to normal-hearing controls. In addition, the counts of the remaining spiral ganglion cells were significantly correlated with the maximum diameter of the cochlear (p = .0006), vestibular (p = .001), and eighth cranial nerves (p = .0003). The regression equation estimated that 25% of the variance of the spiral ganglion cell count was predicted by the maximum diameter of the eighth nerve. Although the results of this study suggest that preoperative radiographic imaging of the diameter of the eighth nerve may be helpful in predicting the residual spiral ganglion cell count, the wide variability of diameters of the eighth nerve in hearing and deaf subjects militates against this theoretic usefulness.     

Chronological changes of stimulation levels in prelingually deafened children with cochlear implant

This study investigated changes in long-term cochlear implant MAPs (values of the program to stimulate electrodes) in children, and examined whether there were significant differences between children and adults. Ten prelingually deafened children (aged from 2.7 to 7.8 years) who received the Nucleus 22 cochlear implant at Kyoto University between 1996 and 1998 participated in this study. Behavioral thresholds (T levels) and maximal comfortable levels (C levels) were evaluated at 3 months post-implant, and then every 6 months up to 4 years. Ten adult cochlear implant users were also evaluated as a control group. All subjects had used their implant for at least 4 years after device connection. All prelingually deafened children demonstrated slower but continuous improvements in speech perception and production abilities during the test period. T levels became stable at 30 months post-implant in children and at 24 months post-implant in adults. C levels became stable at 6 months post-implant in children and within 3 months post-implant in adults. In conclusion, T levels of prelingually deafened children became stabilized 30 months post-implant, while C levels stabilized 6 months post-implant. MAPs of prelingually deafened children were stabilized 30 months post-implant, which was longer than that in adult cochlear implant users.     

Telephone use and the factors influencing it among cochlear implant patients

Abstract

Objective

To investigate telephone use in cochlear implant patients and to determine factors most likely to influence telephone use.

Methods

Surveys were mailed to 504 cochlear implant patients treated at Sunnybrook Health Sciences Hospital.

Results

Two hundred four patients returned surveys (49%), 87% were classified as telephone users. No differences were found in age, pre-implant hearing characteristics, and the majority of post-implant behaviors. Education and post-implant sound perception scores were found to be significantly different (P < 0.05) between telephone users and non-users.

Discussion

Telephone use among cochlear implant patients shows a positive increase compared to previous studies. In addition, we find that higher attained education and post-implant hearing scores to be independently correlated to telephone use.     

Anatomical variations of landmarks for implantation at the cochlear nucleus

A knowledge of the microanatomy of the cochlear nucleus complex and its variations is essential for successful implantation and for the design of stimulation devices. One hundred cerebellopontine angle specimens were dissected under surgical conditions using the Zeiss NC31 surgical microscope. The topographical anatomy of the exit of the vestibulocochlear nerve, the cochlear nucleus and the surface of the medulla and their relation to the surrounding structures was recorded and measured. The mean distances between the exits of the VIIth and VIIIth cranial nerves were 4.7 +/- 0.9 mm, between the VIIth and IXth 6.3 +/- 1.2 mm and between the VIIIth and IXth 5.5 +/- 1.0 mm. The visible area of the cochlear nucleus covered a square of 10.0 +/- 2.9 by 3.3 +/- 1.0 mm. A major AICA-loop had to be re-routed in 17 per cent of specimens. The taenia of the choroid plexus was present in 92 per cent and had to be cut in 51 per cent in order to enter the foramen of Luschka, that had a mean size of 3.5 by 2.0 mm. It was wide open in 24 per cent, open only after incision of the arachnoid in 53 per cent, functionally closed but opened by extensive dissection in 18 per cent and anatomically occluded in five per cent of the specimens. The typical straight vein at the cochlear nucleus leading to the entrance of the foramen of Luschka was found in 76 per cent of specimens. Constant anatomical landmarks are very helpful for finding the cochlear nucleus, but variations may endanger dissection and implantation in a remarkable number of cases.     

REZ-1人工耳蜗电极植入方法的改进研究

目的 探讨使REZ-1人工耳蜗电极靠近蜗轴的植入方法.方法 22例尸头标本CT扫描测量耳蜗直径后,植入REZ-1人工耳蜗电极,完成植入后回撤1～2个电极环,耳蜗位摄片,测量蜗轴与电极环之间距离是否有所改变.测量60例CT扫描显示一侧中耳、内耳结构正常病例的耳蜗直径.结果 22例标本中3例植入27个电极环,19例植入28个电极环.回撤电极后,与回撤前相比17例标本中第12至第19个电极环与蜗轴的距离减小(配对t检验,P<0.01),该17例标本的耳蜗直径均小于9.50 mm;而耳蜗直径大于9.60 mm的5例标本均没有出现电极环靠近蜗轴的改变.17例电极回撤后靠近蜗轴的标本耳蜗直径为9.11(0.57)mm[中位数(四分位数间距),下同],另外5例标本耳蜗卣径为9.78(0.28)mm,二者差异具有统计学意义(Mann-Whitney秩和检验,P<0.001).60例正常耳蜗直径(x±s)为(9.04±0.45)mm,90%小于9.50 mm.结论 REZ-1人工耳蜗电极植入后回撤电极的植入方法可以使耳蜗直径小于9.50 mm的患者底回内部分电极环靠近蜗轴.术前CT扫描测量耳蜗直径可以为REZ-1人工耳蜗电极选择植入方法提供帮助.     

Advantages of magnetic resonance imaging over computed tomography in preoperative evaluation of pediatric cochlear implant candidates.

OBJECTIVES: To compare magnetic resonance imaging (MRI) to high-resolution computed tomography (HRCT) in the preoperative evaluation of pediatric cochlear implant candidates. METHODS: The charts of pediatric cochlear implant candidates evaluated between July 1, 2000 and November 30, 2003 with an MRI scan of the inner ear were included in the study. Fifty-six patients were included. Associated HRCT scans were examined. Abnormalities of the cochlea, cochlear nerve, endolymphatic sac, endolymphatic duct, vestibule, and modiolus were noted. A pediatric neuroradiologist gave an opinion as to whether patients with anomalies seen with MRI but without associated HRCT would have been identified by HRCT. RESULTS: Of the 112 temporal bones imaged with MRI, the following abnormalities were encountered: 32% (36/112) had abnormalities of the cochlear turns, 30% (34/112) had abnormal signal in the modiolus, 23% (26/112) had abnormal vestibulae, 16% (18/112) had abnormal endolymphatic ducts, 15% (17/112) had abnormal endolymphatic sacs, 12% (13/112) had abnormalities of the cochlear nerves, 29% (17/56) had abnormalities of the brain. HRCT cannot directly evaluate the cochlear nerve. Available HRCT findings were combined with radiologic opinion and compared with MRI findings. The percentages of abnormalities identifiable by HRCT when compared with those seen with MRI are cochlea 42% (15/36), modiolus 35% (12/34), vestibulae 88% (23/26), endolymphatic duct 100% (18/18), and endolymphatic sac 6% (1/17). CONCLUSION: MRI is more sensitive and specific in diagnosing soft tissue abnormalities in the inner ear than HRCT in cochlear implant candidates (Fig. 4). Moreover, the abnormalities detected with MRI are more likely to influence the implantation process (e.g., asymmetric nerve aplasia, cochlear obstruction). (Figure is included in full-text article).     

Magnetic resonance imaging versus computed tomography in pre-operative evaluation of cochlear implant candidates with congenital hearing loss

Recent reports indicate that the cochlear nerve may be absent in some cases of congenital sensorineural hearing loss. The aim of this prospective study was to determine the incidence of cochlear nerve anomaly in cochlear implant candidates with congenital hearing loss using magnetic resonance imaging (MRI). Twenty-seven patients with congenital profound bilateral sensorineural hearing loss who were being evaluated for the cochlear implant procedure were studied. These patients had high-resolution computerized tomography (CT), through the petrous bone in axial sections. MRI examinations consisted of T1 and turbo spin echo (TSE) T2-weighted 3 mm axial images, and additional 3D Fourier Transform T2-weighted TSE sequences obtained on three different planes (axial, perpendicular and parallel to the internal auditory canal (IAC) i.e. oblique sagittal and coronal, respectively) for the purpose of cochlear nerve demonstration. Results showed that all of the 14 patients with normal CT of the temporal bone, had four distinct nerves in the distal part of the IAC on TSE-MRI. Thirteen patients demonstrated various bony malformations of the cochleovestibular system on CT. MRI revealed the absence of the cochleovestibular nerve in four patients where the IAC was very narrow or completely absent on CT. One patient with severe Mondini malformation who had an enlarged IAC demonstrated an isolated absent cochlear nerve.     

Use of MRI to determine cochlear duct length in patients undergoing cochlear implantation

Objectives: It is recognised that CT can be used to determine the cochlear duct length (CDL) when selecting an electrode for cochlear implantation. It is the practice of our institution to routinely use MRI as the sole modality of pre-operative imaging in the assessment of children referred for consideration of cochlear implantation. We therefore wanted to determine whether MRI could be reliably used to determine cochlear duct length.

Methods: An analysis of 40 ears that had undergone MRI and CT of the temporal bones was undertaken. The diameter of the basal turn was independently measured for each ear using the two modalities, and CDL was then calculated.

Results: The mean error of measurement was 0.26?mm (range 0–0.8?mm), leading to a difference in calculated CDL of 0.96?mm (range 0–2.92?mm). CDL did not predict full insertion of 28?mm cochlear implant electrodes in 30 ears.

Conclusions: MRI can be used to reliably determine cochlear duct length.     

The effect of cochlear implantation on music perception by adults with usable pre-operative acoustic hearing

This study investigated the change in music perception of adults undergoing cochlear implantation. Nine adults scheduled for a cochlear implant (CI) were assessed on a music test battery both prior to implantation (whilst using hearing aids; HAs), and three months after activation of their CIs. The results were compared with data from a group of longer-term CI users and a group of HA-only users. The tests comprised assessments of rhythm, pitch, instrument, and melody perception. Pre-to-post surgery comparisons showed no significant difference in the rhythm, melody, and instrument identification scores. Subjects’ scores were significantly lower post-implant for ranking pitch intervals of one octave and a quarter octave (p=0.007, and p<0.001, respectively), and were only at chance levels for the smaller interval. However, although pitch perception was generally poorer with a CI than with a HA, it is likely that the use of both devices simultaneously could have provided higher scores for these subjects. Analysis of the other tests’ results provided insights into factors affecting music perception for adults with severe to profound hearing impairment.     

The effect of cochlear implantation on music perception by adults with usable pre-operative acoustic hearing

This study investigated the change in music perception of adults undergoing cochlear implantation. Nine adults scheduled for a cochlear implant (CI) were assessed on a music test battery both prior to implantation (whilst using hearing aids; HAs), and three months after activation of their CIs. The results were compared with data from a group of longer-term CI users and a group of HA-only users. The tests comprised assessments of rhythm, pitch, instrument, and melody perception. Pre-to-post surgery comparisons showed no significant difference in the rhythm, melody, and instrument identification scores. Subjects' scores were significantly lower post-implant for ranking pitch intervals of one octave and a quarter octave (p=0.007, and p<0.001, respectively), and were only at chance levels for the smaller interval. However, although pitch perception was generally poorer with a CI than with a HA, it is likely that the use of both devices simultaneously could have provided higher scores for these subjects. Analysis of the other tests' results provided insights into factors affecting music perception for adults with severe to profound hearing impairment.     

Effects of stimulation by cochlear implant on the cochlear nerve

Degeneration of the cochlear nerve before and after placement of the cochlear implant might influence the efficacy of the device. We examined histological characteristics, including the caliber of the cochlear nerve fibers of the central segment proximal to the porus acusticus, in three profoundly deaf patients. Two of them used a cochlear implant for many years longer in one ear than in the other, and one used an implant in one ear only. No qualitative or quantitative differences between the two sides were found. However, in all three cases we found that the cochlear nerves on both sides were substantially degenerated. These results indicated no noticeable effects of stimulation by the cochlear implant on the central portion of the cochlear nerve.     

Auditory learning and adaptation after cochlear implantation: a preliminary study of discrimination and labeling of vowel sounds by cochlear implant users

This study examined two possible reasons underlying longitudinal increases in vowel identification by cochlear implant users: improved labeling of vowel sounds and improved electrode discrimination. The Multidimensional Phoneme Identification (MPI) model was used to obtain ceiling estimates of vowel identification for each subject, given his/her electrode discrimination skills. Vowel identification scores were initially lower than the ceiling estimates, but they gradually approached them over the first few months post-implant. Taken together, the present results suggest that improved labeling is the main mechanism explaining post-implant increases in vowel identification.     

Auditory Skills Checklist: clinical tool for monitoring functional auditory skill development in young children with cochlear implants

OBJECTIVES: The Auditory Skills Checklist (ASC) was developed to address the need for tools to evaluate functional auditory skill progress in very young children with sensorineural hearing loss. We describe the development, validation, and utility of the ASC for use in young children with cochlear implants. METHODS: Using the ASC, we measured auditory skills in 37 subjects who received cochlear implants at no more than 36 months of age. Repeated measures analysis was conducted to determine expected auditory skill development after implantation. Interrater reliability was tested on a small subset. The ASC was compared to the Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS) to determine its validity in measuring functional auditory skills. RESULTS: The ASC had excellent internal consistency (Cronbach's alpha, 0.98) and interrater reliability (intraclass correlation coefficient, 0.99), and was highly correlated with the IT-MAIS (r = 0.90). According to the repeated measures analysis, children who received a cochlear implant at 36 months of age or earlier were expected to increase their ASC score by 8 points every 3 months (beta coefficient, 8.3; p < .001). CONCLUSIONS: The ASC is a clinically relevant and easily administered tool for assessing the functional auditory skills of young children with a cochlear implant. By assessing auditory skill development over time with the ASC, we can better realize expectations for a particular child based on his or her age, hearing loss level, and management strategies in place.     

Auditory brainstem implant as a salvage treatment after unsuccessful cochlear implantation.

OBJECTIVE: The present article investigates on an individual basis the performance achieved with the auditory brainstem implant in patients who had been treated unsuccessfully with a cochlear implant. STUDY DESIGN: An intrasubject comparison between results achieved with the cochlear implant and the auditory brainstem implant is reported. SETTING: Tertiary referral care. PATIENTS: Five subjects were fitted with an auditory brainstem implant in our department because of the poor results achieved with cochlear implants. Two were children, one with bilateral cochlear nerve aplasia and one suffering from auditory neuropathy. Three were adults with complete cochlear ossification. INTERVENTION: A retrosigmoid approach was used in all subjects. Electrically evoked auditory brainstem responses and neural response telemetry were used to monitor electrode positioning. RESULTS: No complications were observed due to implantation surgery or related to activation or long-term use of the auditory brainstem implant. Auditory sensations were induced in all patients with varying numbers of electrodes (from 9-16). In all three adults, the cochlear implant did not allow either word/sentence discrimination or speech tracking, whereas the auditory brainstem implant permitted discrimination of two- or three-syllable words with scores from 85 to 100%. In the two adults with a follow-up of 5 and 6 months after auditory brainstem implant activation, the open-set sentence recognition scores (auditory-only mode) were 70% and 100%, respectively, and the speech-tracking scores were 27 and 40 words/min, respectively. One patient with a follow-up of only 3 months scored 0% in both sentence recognition and speech tracking. The two children who had achieved no hearing ability with the cochlear implant were already able to detect sounds and words as early as 2 months after activation of the auditory brainstem implant and are showing progressive improvement in their performance. CONCLUSION: Auditory brainstem implantation may be a very powerful rehabilitative treatment after cochlear implant failure. The possibility of using the auditory brainstem implant as first-choice therapy in some categories of deaf patients (e.g., subjects with auditory neuropathy or cochlear ossification) who are currently treated with cochlear implantation is discussed.     

Topography of vestibulocochlear nerve fibers in the posterior cranial fossa

In the posterior cranial fossa, the separation of the vestibular and cochlear subdivisions of the eighth nerve is clear in about 75% of cases. Although in the remaining cases the vestibulocochlear cleavage plane is not visible macroscopically, the large-fibered vestibular subdivision and the small-fibered cochlear subdivision are well recognized in histological sections. Within the cochlear subdivision, some fibers of large caliber are mixed with fibers of small caliber in a region we named the “overlapping zone.” We studied, histologically, cross sections of the intracranial portion of six eighth nerves at about 5 mm proximal to the porus acusticus. A computerized video system was used to measure the diameters of the fibers of the vestibular and cochlear subdivisions localized at different distances from the vestibulocochlear cleavage plane. The overlapping zone is located within the cochlear subdivision adjacent to the vestibulocochlear cleavage plane. It has a pear-like shape, with the larger part occupying the anterosuperior part of the cochlear subdivision. The mean cross-sectional area of this zone in our six samples is about 0.4 mm², which is approximately 23% of the area of the cochlear subdivision. The thickness of the zone in the superior-inferior direction ranges from 0.23 mm to 0.55 mm. The parameters of the described overlapping zone should be taken into consideration in vestibular neurectomy, in which complete sectioning of the vestibular fibers is important.     

Is psychological status a determinant of speech perception outcomes in highly selected good adolescent cochlear implant users?

OBJECTIVE: The main purpose of this study was to assess the relationship between the speech perception skills and state-trait anxiety in cochlear implant user adolescents who were highly selected good candidates. The impact of preoperative speech perception ability on postoperative speech perception and state-trait anxiety status were also examined. SUBJECTS AND METHODS: The subjects for this study were 25 consecutively chosen congenitally profoundly deaf adolescents (12 boys, 13 girls) who received nucleus multi channel cochlear implants and were followed for at least a year at Hacettepe University. Daily Sentences in Turkish and State-Trait Anxiety Inventories (STAI) were administered to subjects after 12-72 months (mean: 35.28+/-18.27) of implant use. RESULTS: The trait and state anxiety scores were matched with the relative rank of normal hearing subjects' trait-state anxiety scores and the analysis of post-implant state-trait anxiety findings shows that both state and trait anxiety scores were widespread but still in normal range. The correlation between trait, state anxiety scores and speech perception ability was not statistically significant in adolescent cochlear implant users. However, their preoperative speech perception scores were significantly correlated with their postoperative speech perception abilities. CONCLUSION: The majority of adolescents, in this study, achieved varying degrees of open-set speech recognition and made greater gains than their previous auditory experience with hearing aids. Also, the indirect positive effects of early identification-amplification, communication therapy and counseling programs on their personal well-being is clearly observed from the outcomes of their state and trait anxiety scores. As a result of correlating the trait and state anxiety levels with pre- and post-implant speech perception skills, a significant negative correlation was expected. However, no statistical correlation was found between speech perception skills and the psychological outcomes. This result may be the indicator of the positive effect of the early habilitation-parental support and cochlear implant on the quality of life as the adolescents involved in this study were developmentally and audiologically ready for implantation. The present study provides understanding of the audiological and social-emotional influences of early identification and habilitation programs on adolescents with cochlear implants.     

Auditory neuropathy characteristics in children with cochlear nerve deficiency

OBJECTIVE: To describe a group of children exhibiting electrophysiologic responses characteristic of auditory neuropathy (AN) who were subsequently identified as having absent or small cochlear nerves (i.e., cochlear nerve deficiency). DESIGN: A retrospective review of the clinical records, audiological testing results, and magnetic resonance imaging (MRI) studies. Fifty-one of 65 children with AN characteristics on auditory brain stem response (ABR) testing had MRI available for review. Nine (18%) of these 51 children with ABR characteristic of AN have been identified as having small (N = 2; 4%) or absent (N = 7; 14%) cochlear nerves on MRI. RESULTS: Of the nine children with cochlear nerve deficiency, five (56%) were affected unilaterally and four (44%) bilaterally. Eight of nine presented after failing a newborn infant hearing screening, whereas one presented at 3 yr of age. On diagnostic ABR testing, all 9 children (9 of 13 affected ears; 69%) had evidence of a cochlear microphonic (CM) and absent neural responses in at least one ear. In the unilateral cases, AN characteristics were detected in all affected ears. In bilateral cases, at least one of the ears in each child demonstrated the AN phenotype, whereas the contralateral ear had no CM identified. Only one ear with cochlear nerve deficiency had present otoacoustic emissions as measured by distortion-product otoacoustic emissions. In children with appropriate available behavioral testing results, all ears without cochlear nerves were identified as having a profound hearing loss. Only 4 (31%) of the 13 ears with cochlear nerve deficiency had a small internal auditory canal on MRI. CONCLUSIONS: Children with cochlear nerve deficiency can present with electrophysiologic evidence of AN. These children frequently refer on newborn screening examinations that use ABR-based testing methods. Similar to other causes of AN, diagnostic ABR testing will show a CM with absent neural responses. Given that 9 (18%) of 51 children with available MRI and electrophysiologic characteristics of AN in our program have been identified as having cochlear nerve deficiency makes this a relatively common diagnosis. These findings suggest that MRI is indicated for all children diagnosed with AN. Moreover, electrophysiologic evidence of unilateral AN in association with a profound hearing loss should make the clinician highly suspicious for this problem. Although children with cochlear nerve deficiency who have a small nerve may benefit from cochlear implantation or amplification, these interventions are obviously contraindicated in children with completely absent cochlear nerves.     

The bony cochlear nerve canal in children with absent or hypoplastic cochlear nerves

Objective

To correlate presence and size of the bony cochlear nerve canal [BCNC] with size of the internal auditory meatus [IAM] on CT in children with absent or hypoplastic cochlear nerves [CNs] as compared to age matched controls.

Methods

This retrospective case-notes review was based in the departments of Cochlear Implantation and Neuroradiology at a tertiary paediatric hospital. Twenty-five ears of fifteen children (subjects) with profound sensorineural deafness (SND) and absent or hypoplastic CN on MRI scan were compared to age matched controls. Two groups of controls were included; a control group of nineteen ears of twelve children with normal hearing or conductive hearing loss [control group 1] and a second control group of twenty one ears of eleven children with severe to profound hearing loss related to GJB2 mutations [control group 2]. Both control groups had evidence of the presence of the CN. Two neuroradiologists independently assessed presence and size of BCNC and IAM on CT and presence of CN on MRI in subjects and controls. The BCNC and IAM size was compared between subjects and both control groups. The presence of BCNC was correlated with the IAM size on CT, presence/absence of CN on MRI and audiological evaluation in subjects.

Results

The mean IAM width was significantly smaller in subjects as compared to controls. The BCNC was absent in 17/25 subject ears and present in all control ears. Absent BCNC correlated with a narrow IAM in 13/17 subject ears. Presence of the BCNC supported presence of a CN although this was not seen on MRI. However, BCNC absence may be associated with presence of a CN as was seen in two subject ears. Five subject ears out of 22 [22%] with absent CN on MRI had other evidence of a present cochlear nerve.

Conclusions

BCNC is an additional parameter to assess presence of the cochlear branch of the CN. Presence of the BCNC may indicate cochlear nerve presence. Caution should be used in assessing candidacy of cochlear implants based on MRI alone and a combination of imaging and audiological tests should be used to assess presence of the CN.     

A survey of speech and other auditory perception assessment materials used by cochlear implant centers

A questionnaire assessing the various auditory perception materials used by cochlear implant centers in evaluating cochlear implant candidates and patients was developed, pilot tested, and mailed in August, 1985, to 135 cochlear implant centers. After a follow-up, there was a 45% return rate. The questionnaire sampled responses pertaining to the respondents' demographics, the types of assessment materials they used, and their opinions about speech and other auditory perception tests for evaluating cochlear implant patients. The data revealed that most centers use the same tests repeatedly for both pre- and post-implant assessments. Several factors relating to the tests and their administration were identified. Only 36% of the centers expressed satisfaction with the currently-used materials. The tests most frequently used were not necessarily considered to be the best or most appropriate for evaluating cochlear implants. Most respondents stated a need for the development of new test materials, and some suggestions were provided.     

An investigation into the effect of limiting the frequency bandwidth of speech on speech recognition in adult cochlear implant users

The purpose of this study was to investigate the effect of the limited-frequency bandwidth employed by telephones (300-3400 Hz) on speech recognition in adult cochlear implant users. The Four Alternative Auditory Feature (FAAF) test was used in four conditions: unfiltered and in three filtered conditions of 300-4500 Hz, 300-3400 Hz and 300-2500 Hz. Ten subjects implanted with the Nucleus CI24M device and 10 normal-hearing listeners were assessed to examine differences between word discrimination scores in each condition. Scores obtained from the 300-3400-Hz and 300-2500-Hz filtered conditions were significantly worse than those with unfiltered speech for the cochlear implant subjects, decreasing by 17.7% and 21.4%, respectively, from scores with unfiltered speech. By contrast, the normal-hearing listeners did not experience difficulties in discriminating between words in any of the conditions. Analysis of the word errors demonstrated that the reduction in implant subject scores with bandwidth arose from errors in place of articulation. Filtering speech in this way has a significant effect on speech recognition for cochlear implant subjects but not normal-hearing listeners. Hence, the limitations of the normal telephone bandwidth can be expected to have a negative effect on speech recognition for cochlear implant users using the telephone.