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Cochlear implant mapping

Posted May 03 2010 4:12pm

I’ve had 5 “mapping” sessions since activation. A mapping is a reprogramming of the cochlear implant, to readjust the electrical stimulation limits of the electrodes as each user’s brain adapts to sound and fibrous tissue grows over the internal implant. Mappings are typically carried out once a week for the first 6 weeks, then every few months, then twice annually.

At each mapping I was given increased volume and it was an opportunity to address any concerns with the audiologist. This was followed by a coffee break in the hospital cafe then a speech therapy session. I have one more mapping session this week, then my next one is in June when I have my 3 month check.

It’s been a rollercoaster ride. I’ve started with beeps and pushed so hard that I got a constant whine when I put the implant on. This set me back and I had to slowly build up my tolerance again of high frequency sounds from zero, bit by bit, and have successfully avoided a reocurrence of the whine. I have not yet reached full volume, there is still some way to go, which is kind of scary. I found last week quite difficult as everything seemed too loud and I started feeling stressed, but I hung in there and carried on wearing the cochlear implant until I got used to the increased sound levels.

Inreased sound levels can be problematic for cochlear implant users because they are more sensitive to loudness changes. A hearing person can hear a wide range of sounds from very soft whispers to loud rock bands; this dynamic range of hearing is about 120dB (normal speech is within the 40-60dB range). However, a cochlear implant processor’s input dynamic range (IDR) or sound window is limited to an electrical current of 30dB, and 120dB needs to be compressed into this. Therefore the cochlear implant user is more sensitive to changes in loudness than a hearing person.

If the IDR is small, sounds outside the IDR need to be omitted or compressed; sounds that are too quiet will be cut off, and sounds that are too loud will be compressed and will sound distorted. The 3 main brands of cochlear implants have different IDRs; Advanced Bionics has 96, MedEl 75, and Cochlear 45. I currently have my IDR set at 60.

What actually happens in a mapping session? I replace my processor’s battery with a direct connect input lead to the audie’s computer and put the processor back on my head. (Yeah, this freaked ME out the first time I did this).

The audie’s software will reprogramme my implant’s internal electrode array.

My cochlear implant has 16 electrodes and when each one is stimulated, I will sense each stimulation as a beep.
The audie will set the Threshold (T) levels [to access soft speech and environmental sounds] and Comfort (M or C) levels [the amount of electrical current required to perceive a loud signal] for each electrode by judging the most comfortable and the highest stimulation I can tolerate – the most comfortable and loudest beeps I can stand to listen to.

I use the loudness scaling chart to indicate to the audiologist which level each stimulation correlates to, ranging from ‘Just Audible’ to ‘Too Loud’.

Then the audie ensures the C levels are similar in terms of my perception, so that the volume is the same in each electrode – I was able to tolerate very high levels of high frequency sounds this week but she brought these back down, otherwise everything would have sounded weird and unbalanced.

This mapping method is rather tedious and drawn out over several months. Clarujust is new software (currently in FDA trial) from Audigence Inc where the patient and processor are interfaced to a computer and words are played and repeated as heard, the software adjusting the map accordingly. Mapping this way reportedly takes 30 minutes. This software can be used by all hearing aid and cochlear implant companies except Advanced Bionics, however Phonak signed up with Audigence Inc this year prior to the Advanced Bionics/Sonova acquisition.

When a mapping is new, it tends to sound louder, until I get used to it. It takes 3 days to get used to a new mapping, then I find loud sounds have become softer and more tolerable, and I can hear a wider range of soft sounds. It is uncomfortable turning up the volume of life to the max every few days, I still have to brace myself for the jolt first thing in the morning, making the transition from complete silence to a full wham-bam-thank-you-ma’am-technicolour river pouring into my brain. Amanda’s Tip of the Day: If you wake with a hangover, take your time to put on your CI and turn down the volume. It helps (a little).

It’s an amazing learning process as I am also trying to identify sounds as well, discovering amazing new ones, and learning to discriminate between things that sound similar to me. My hearing is like a baby, it needs time to learn and grow, but it can be fun too.

Erber’s model set forth 4 levels of auditory skill development;

I have now reached the second level, I am hearing things but finding it difficult to discriminate between some sounds. Obviously, this means I am still lipreading. In my speech therapy session this week, I discovered I can’t distinguish between Gear v. Dear, tIme v. tAme. I can listen and fill in a word missing in a written sentence, but listening to a whole sentence and being given one written word is more difficult. With hearing aids, both tasks would have been impossible.

In addition to mapping, my progress is occasionally evaluated with an audiogram and speech perception performance with the cochlear implant in a soundproof booth. These tests assist the mapping process and indicate any further adjustments required. I expect I’ll have this done this week, and hope to have improved upon the 18% I achieved in my last speech perception test.

I was programmed with ClearVoice last week but am still adjusting to my new mapping, so I have just been ‘tasting’ this wonderful addition. I tried it on the train; the roar of the train engine and clashing sounds (brakes or pressure pads? – haven’t worked this sound out yet) dropped away significantly and I could clearly hear voices around me. It was awesome. Yesterday, I was sitting by a window and became conscious of this sound. I realised it was the rain spitting outside. In the garage, I could hear the drumming of the rain on the roof and the traffic outside. With ClearVoice on, the traffic became very quiet and the rain became a very clear high PLINK PLINK PLINK, and a lower PLONK PLONK when it came through a hole in the roof and landed on an object. Again, awesome!

Try out the ClearVoice demo for yourself. Don’t forget to say the mandatory WOW!

Shanti is waiting for her cochlear implant operation date and works as a personal trainer and complementary therapist. She gave me a super aromatherapy massage yesterday and I left feeling very relaxed. As soon as I left, I plugged into my iPod and was amazed to hear that the tinny / Donald Duck tone of vocals had gone from a lot of songs. Perhaps there is a link between relaxation and better hearing. Today, voices sound largely normal and it’s so so so NICE to have some normality again!

Photos courtesy of Byron


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