Do Cochlear implants work with hearing aids? Yes, they do!
Teresa Ching
Submitted to CONTACT, Spring issue, 2001,
to be published by Cochlear Implant Club International, Inc.
You may be a parent of a hearing-impaired child who has a cochlear implant, or a professional who works with hearing-impaired children, or you may have a cochlear implant yourself and would like to know what we are up to in Australia regarding the use of cochlear implants with hearing aids. The following provides you with answers to some of the questions that you may like to ask on this issue. Although a parent’s perspective has been assumed, the content applies equally well to children and adults, and ‘my child’ can be used interchangeably with ‘me’ or ‘I’.
Now that my child wears a cochlear implant, why would he (she) need to wear a hearing aid in the non-implanted ear?
A child who has a cochlear implant in one ear and severe hearing loss with no amplification in the other ear can only listen with one ear. Try plugging one ear when talking to a friend in a noisy environment and you’ll soon notice that it becomes difficult to understand what your friend is saying. Using two ears to listen makes it easier to listen in noisy situations, and makes it easier for you to locate where sounds come from. Your child cannot enjoy these advantages that you have when he or she listens with amplification only in one ear.
Furthermore, if your child does not make use of the residual hearing in the non-implanted ear, that ear may gradually lose its ability to analyse sounds. Without amplification, the ear is not stimulated by sounds and it won’t be able to work so well if and when your child needs to call on it in the future.
Wouldn’t it be confusing for my child to hear an acoustic input via a hearing aid and an electrical input via a cochlear implant at the same time?
The National Acoustic Laboratories (NAL) and the Children’s Cochlear Implant Centre (CCIC) in Australia conducted a study recently to examine whether the use of a hearing aid would interfere with the use of a cochlear implant in contralateral ears. We did not find any evidence to indicate that the children perceived speech poorer when using a cochlear implant with a hearing aid in opposite ears compared to using a cochlear implant alone. There were no compliance problems – all children used cochlear implants and hearing aids in their everyday life and have had no problems managing both devices.
I must mention that we have adjusted the hearing aids with the cochlear implants for each individual to ensure that they work well together.
Is there any evidence showing that the use of a hearing aid with a cochlear implant is better than the use of a cochlear implant alone for children?
The study conducted by NAL and CCIC showed that children could hear speech better in noise when wearing hearing aids with cochlear implants than when wearing cochlear implants alone. The average hearing thresholds of these children at 500 Hz was 94 dB HL, at 1000 Hz was 105 dB HL, and at 2000 Hz was 115 dB. Four children did not have measurable hearing thresholds at 2000 Hz.
The following graph shows the sentence scores of the children when using cochlear implants and unadjusted hearing aids (CUA), cochlear implants and adjusted hearing aids (CIHA), hearing aids alone (HA) and cochlear implants alone (CI). The children listened to sentences presented in a speech babble noise, with speech presented at 10 dB above the level of the noise. Eight children performed much better in the CIHA condition than in the CI condition. The remaining three performed equally well in both conditions. The hearing aid benefit obtained was not significantly correlated with hearing thresholds in the non-implanted ear. It appears that even if no measurable hearing thresholds can be obtained beyond 1000 Hz, some hearing aid benefit can still be obtained.
In a laboratory test that assessed horizontal localization, it was found that the children could locate the source of sounds better when using hearing aids with cochlear implants than when using cochlear implants alone. Most importantly, the children’s parents observed that the children functioned more effectively in everyday communicative situations when using hearing aids with cochlear implants than when they were using cochlear implants alone. One parent said that her child "is now happy to converse with unfamiliar persons". Comments that other parents made about their own children included, "she picks up other people’s conversations", "she is more alert", "he can answer my questions without even looking up", "I can talk to him without having to get his attention first", and "I don’t need to repeat so often". One parent had this to say of her child, "he is like a normal kid". A detailed description of the methods used and the results of this study can be found in an article submitted to Ear & Hearing Journal (Ching, Psarros, Hill, Dillon, & Incerti, submitted).
All of these evaluation results were obtained after the children’s hearing aids were adjusted to work with the cochlear implants they were wearing.
You spoke about adjusting hearing aids to work with cochlear implants. Did the adjustments help?
Yes, all children in the study performed better in speech tests and in everyday life after the hearing aids have been adjusted to work with the cochlear implants compared to their scores before the adjustment. This can be seen in the figure above. For 9 out of the 11 children, the column for CIHA (cochlear implants with adjusted hearing aids) is taller (higher score) than the CUA (cochlear implants with unadjusted hearing aids) column.
One child commented immediately after the adjustment, "It’s (hearing aid) much better than before". Another child said "I really notice the advantage of wearing both now". An older child commented "it’s more balanced now", and a different child simply said "I can hear better".
Could you outline the steps for adjusting hearing aids to work with cochlear implants?
There are two steps to the adjustment of hearing aids with cochlear implants. Hearing aids with wide dynamic range compression should be used with all children.
The first step aims to optimise the frequency response in a child’s hearing aid to ensure that it amplifies the input signal in a way that makes speech easiest for the child to understand. A paired comparison procedure is used to identify the appropriate frequency response. Our results indicate that the NAL prescription (Byrne & Dillon, 1986; Byrne, Parkinson, & Newall, 1991; Dillon, 1999) provides an adequate frequency response for amplification.
The second step aims to equate the loudness of speech in the ear with a hearing aid to that with a cochlear implant. The hearing aid gain is adjusted so that when speech is presented at 70 dB SPL, it sounds equally loud in the ear with a hearing aid to that with a cochlear implant.
| The child wears a hearing aid connected to a programming device. Gain is adjusted on-line so that speech is judged by the child to sound equally loud in the ear with a hearing aid to that with a cochlear implant. |  |
Sounds fairly straight forward to me. Can you perform these tests to adjust hearing aids for all children?
You can do these tests with children who are older than six years of age and of course, adults as well. For younger children, the frequency response can be set according to the NAL prescription (NAL-NL1 for non-linear hearing aids). Currently, NAL and CCIC are developing a procedure for balancing the loudness of sounds between ears for children under six years. Stay tuned.
Do you know if the hearing aid benefits obtained by children with cochlear implants apply similarly to adults with cochlear implants?
Yes, we are now in the process of assessing a group of adults who use cochlear implants and hearing aids in opposite ears. Their hearing aids have been adjusted using the same procedure that I described above. The NAL prescription provides an appropriate frequency response in their hearing aids, and the adjusted gain provides a balanced input to both ears in terms of loudness. The speech results indicated that the adults were getting much hearing aid benefit especially when listening to speech in noise. The adults also commented on the improved quality of speech when they used a cochlear implant with a hearing aid compared to using a cochlear implant alone.
Where can I (or my audiologist) get more information about using hearing aids with cochlear implants?
| You can email -
Teresa Ching at Teresa.Ching@nal.gov.au |
Colleen Psarros at Colleen@ccic.nsw.gov.au |
Reference
Byrne D & Dillon H (1986). The National Acoustic Laboratories’ (NAL) new procedure for selecting the gain and frequency response of a hearing aid. Ear & Hearing, 7: 257-265.
Byrne D, Parkinson A,& Newall P (1991). Modified hearing aid selection procedures for severe/profound hearing losses. In: Studebaker G, Bess F, Beck L (eds). The Vanderbilt Hearing Aid Report II, Maryland, York Press.
Ching TYC, Psarros C, Hill M, Dillon H, & Incerti P (submitted). Should children who use cochlear implants wear hearing aids in the opposite ear? Ear & Hearing.
Dillon H (1999). NAL-NL1: a new procedure for fitting non-linear hearing aids. The Hearing Journal, 52 (4): 10-16.