Bilateral Implants

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Hi Everyone,

The following post is from a VERY experienced audiologist, Fisher,

whom I recently met in Western Australia. He is very involved in the

sequential bilateral implant studies in children in Western Australia, and

he has given me his permission to send some of his findings and insights

regarding this subject to the forums. It's a very interesting read, I hope

you enjoy it. Here 'tis:

" You mentioned when we were together leaving your other ear for future

developments. We have now done 16 children and young adults (up to 24 years

of age) and have learned a few things as you might expect. One of the

things is that it is difficult to " wake-up " an ear after years of lying idle

whilst the other ear has been effectively stimulated for several years.

All my binaural cases are of this type i.e. they have all had a single CI

and then some years later have had a second one. What appears to happen is

that both ears though deaf start of with comparable potential to learn to

discriminate speech BUT if one ear receives all the stimulation the other

ear over a period of time loses this potential in most cases. The research

done by Harvey Dillon with hearing aids appears to show the same phenomenon

of gradual loss of speech discrimination potential in the unstimulated ear

when only one hearing aid is fitted in the case of someone who is

adventitiously deafened (as you were).

I hope you will not resent my poking my nose into your personal case

uninvited but as we have now met I felt I must share these insights with you

as there is as yet not a lot of case knowledge about sequential cochlear

implantation so my group of cases is fairly substantial in the present state

of knowledge. I just feel that based on my findings if you were to consider

a second CI your chances of its giving you all its potential benefits will

be far greater if you have it sooner rather than leaving it till later.

There is not a great deal of point in waiting for more advanced CIs if the

ear has been neglected for too long. I realise you could say in your case

having been very deaf for some 20 years that you have had no great

difficulty wakening up the implanted ear and therefore you might expect the

same to occur no matter when the other ear is implanted. What I wish to

share with you is that there is strong evidence that if the other ear is

left unstimulated it is likely to lose its speech discrimination function

because of the increasing dominance of the successfully implanted " first "

ear.

The advantages of binaural stimulation from a CI are:

1. greater ease of hearing as two ears effectively summate the loudness of

speech whilst each remains at its own output level. What this means in

practice is that both devices working together can be turned down

significantly than when each works alone; the estimate in the research is a

3dB minimum gain in the binaural listening condition increasing to more like

10 dB in a range of listening conditions. Even 3dB whilst it doesn't sound a

lot because it is a logarithmic value in fact is a doubling of the output

intensity so is of great potential value in easing the listening burden on

the separate ears.

2.localisation cues are made possible and effective with a binaural set up;

allied to this is better hearing in noise and improved social conversational

function in a group situation as with two CIs it is much easier to identify

reflexively who has just started to speak as the direction of their voice is

immediately indicated to the binaural implant user. For similar reasons it

is easier to separate the speech one wants to hear from other noise sources

including room noises and the sound of other people talking such as when one

is at a meeting or party or at a venue where there is music playing.

3.another feature which I have observed in my cases is what Harvey Dillon

calls externalisation i.e. when there is effective binaural stimulation the

world sounds far more three dimensional with the sound appearing to come

from various points in the environment whereas with one device most people

appear to perceive the sound more at the ear without information about where

the sound originates. The sound in the latter case appears more flat-planed

or two dimensional than the three dimensional percept created by two devices

working together. This is of considerable psychological significance in the

cognition of envoronmental signals.

When I was a young audiologist in the mid 1950s all the kids had one hearing

aid. Among other workers I did some research to show the great benefits of

having two hearing aids. In only a few years the fitting of two hearing

aids for children became the default fitting. The costs of a second CI are

comparatively much greater than was the case with hearing aids so this will

give administrators more reason to resist the trend to binaural fittings but

I feel it is only a matter of time before the fitting of two CIs becomes the

norm. And probably eventually we will see most cases fitted with two CIs at

the same operation.

After all the Creator decided we all need two ears and I don't think he was

a wasteful planner. We've followed his lead now with two hearing aids so

why not 2 CIs unless there is some good clinical reason to the contrary? "

I contacted again after recieving the above post and asked him whether

or not he thought it would be beneficial for me to wear a hearing aid in my

unimplanted ear until such times as I might consider getting a second

implant. Of course his answer was a resounding YES!

Cheers until next time.

Mischelle in Oz

Progressive loss due to childhood measles

Severe/profound by early 20's - HA's for 30 years!

Nucleus 24 Contour, August 2000 and wearing the ESPrit 3G!

Consumer Advocate

Cochlear Ltd, Sydney, Australia

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