Adjustments explained

When your implant is activated, the audiologist fires up something on a computer and connects a dongle to your processor.  After fooling around with some settings, you may hear some beeps.  And a few minutes later, the audiologist will switch on your microphone, and you will hear sounds! Probably very strange sounds, but it is a start.

Each time you visit the audiologist, you may have some adjustments made to your program settings.  Or you may be lucky enough to get a new strategy or algorithm that promises better hearing in certain types of situations.

Life couldn’t be better, right?

Perhaps you have some particular situation for which you would like to try some minor adjustments.  Or maybe you seem to be missing the crickets on one side, but you can hear them on the other.  A little bit of knowledge about the possible adjustments might give you enough information to stride confidently into the audiologist’s office with some requests.

Please remember that your audiologist is a highly skilled professional, and may choose not to even bother trying some of your suggestions.  But you may have a good idea of what you would like to achieve, and a possible way to do so.

Your hearing with an implant will change during the first weeks and months that you use it.  After that, when things settle down, and you use only one or two programs, you may become very familiar with the sound quality.  And that is when it might be time to start thinking about what you would like to improve.

Always ask the audiologist for printouts of your program settings. Better yet, ask them to print to pdf format and send you the file by email.  If nothing else, you can use them for wrapping paper.  Just one step above that, and they are handy reminders of what you have in each program slot.  And if you read them in more detail, you may find subtle differences that you can try to correlate to the way the programs sound.  Finally, you may be able to use that knowledge to come up with things to try the next time you visit the audiologist.

Whenever you have any changes made, you should keep your prior favorite program in one slot.  You can try a couple of variations in the other slots.  If you decide that you really don’t like them after you give them a chance, you can always go back to your old standby.

Most comfortable loudness

Each electrode can present sound over a range of loudness.  At the upper end, it should be comfortably loud, but not so loud that it would become tiresome after listening at that volume for a while.  If you have experience with hearing aids, where you are always trying (unsuccessfully) to get enough volume, this is a little counterintuitive.  The implant should be comfortable, no matter how loud the sounds around you are.

If the maximum level (M level for Advanced Bionics, C for Cochlear, and MCL for MED-EL) is a little too high, you may tire of wearing the processor.  If it is set even higher, you may experience a twitch near your eye when you hear a loud sound.  It isn’t harmful, but it can be disconcerting.  And if it is pushed even higher, the current may punch through from one turn of the cochlea to another, resulting in a vastly different pitch!

And the M level is not one global adjustment for the whole implant.  Each electrode may have a different M level that you decide is comfortably loud.  The M levels may be set for groups of electrodes at a time rather than individually.  When you are first activated, it is unlikely that you will be able to provide reliable feedback to make fine adjustments to the M level.  After a while, the audiologist may start tweaking individual electrodes.

Threshold of perception

On the opposite side of loudness, there is some stimulation level below which you can’t hear anything.  It isn’t zero.  Each company defines the threshold of perception, or T level, slightly differently.  Measuring the T level is more difficult than measuring the M level.  The faintest sounds may be masked by tinnitus.  Even if you don’t have tinnitus, it can be challenging to detect the softest sounds.  People with normal hearing have the same difficulty.  Some programming systems set the T level to zero, or a fixed percentage of the M level.  Others encourage the audiologist to make some measure of the T level.  All systems have the ability to measure the T level for each electrode.

Most people with hearing loss have a smaller difference between the loudest comfortable sounds and the softest sounds that can be heard than people with normal hearing.  One job of any hearing instrument is to map the wide dynamic range of sounds to the smaller range of the patient.  While the difference (or ratio) of the M and T levels doesn’t seem to have a nice name, we can think of it as the output dynamic range of the implant.

IDR

The microphone can pick up a much larger dynamic range of sound at the input.  The audiologist has control over the input dynamic range, or IDR.  A narrow IDR may reduce unnecessary noise, and limit the sound range to that of the normal variations in speech.  A wider IDR may present a more complete picture of the sound environment.  Narrower IDR may improve speech comprehension if you have trouble with background noise, but it comes at the expense of a feeling of isolation, since you aren’t hearing as many sounds around you.

Clearly each of us will end up with an IDR that suits our own needs.  You may want to try a higher IDR for music than for speech.  Or if you are frequently in a noisy environment, a lower IDR may help.  Of course, each manufacturer has different approaches for dealing with noise, hopefully with better results than a simple reduction in IDR.

Mixing ratio

Most processors have more than one input.  For example, each has at least one microphone, possibly a telecoil, and a direct audio input.  You may want to listen to a music source with the direct audio input, but still have the microphone on just a little bit so that you can hear the telephone ring or somebody calling you.  The audiologist can set the mixing ratio between two of these sources.  You will probably have better luck if you describe what you would like to do (such as listen to music with direct audio input while retaining the ability to hear some external sounds) than if you request a specific mixing ratio.

Advanced Bionics users start out with some mix of the T-mic and the internal mike by default.  Nearly all users independently decide that they prefer 100% T-mic.  If you don’t have a 100% T-mic program, ask for one!

Automatic Gain Control

All implants employ a common algorithm to adjust the gain automatically depending on the overall loudness of the sound.  When you are in a loud environment, the volume is turned down, and vice versa.  Normally AGC should be left enabled.  But if you enjoy classical music, and would like the soft sounds to remain soft, it may be worth disabling the AGC in one program, particularly if you a making other tweaks for that particular situation.  There are some adjustments for the operation of AGC, but they are probably best left to the audiologist.

Other adjustments

Of course, there are many other adjustments possible with each implant.  Largest of all are the myriad strategies.  Most implants have a long history of program strategies of increasing complexity, and hopefully better performance.  It is always worthwhile to try the latest and greatest strategy.  If you are used to an older strategy, the new one may not sound very good at first.  But give it a chance, several weeks at least.  You may then try your old standby and wonder how you were ever able to function at all with it.

Each manufacturer is developing new strategies and algorithms, usually based upon their most recent achievement.  So if you decide that you prefer an older strategy, you may not be able to take advantage of future enhancements.

Individual electrodes can be turned way down or disabled, and electrodes can be reassigned in case the array is folded over inside your cochlea.  The range of the volume control may be modified, or the volume control can be reassigned to sensitivity instead.

Each manufacturer also provides many implant-specific adjustments that are beyond the scope of this guide.  Remember to rely on the expertise of your audiologist.  And read your program settings report to gain an understanding of what you have, and possibly to help you think of things to try at your next visit.

– Howard Samuels

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