#2

Raudrive: I like your explanation up to a certain point. I was under the impression that the older view of unnatural loudness was as you explained…that is; other inner cells were Recruited.

But I thought the newer explanation was that the Outer hair cells also deteriorated allowing the full sound pressure to get to the inner ones which then circuitously connect to the auditory cortex. I think the newer view is that the outer cells modulate and mitigate excessive sound pressure.

Also in play to a minor extent is the muscle that tightens the ossicles when loud sounds are heard. Ed

Please correct me if I am mistaken. Ed

#3

Ed,

You are the reason I went looking for a definition of recruitment. You use the term now and then and I did not know what it meant.

The cut and paste description I inserted sounded like a good explanation of recruitment. If it is not correct I would not know.

The reason I brought this to the forum is if I didn’t understand it, maybe others didn’t either. The article helped me a bunch and explained issues I deal with concerning aids.

Thanks for getting me to thinking.

#4

Yes, understood.

Incidentally: If you drive the fluid filled organ of Corti’s inner hair cells, which is located in the cochlea, hard enough, then working adjacent inner cells will be excited and respond but not at the actual input frequency. Because the patient is hearing only a faint sound which may be distorted, the professional may score this as a valid threshold db loss. This is why pure tone threshold testing is so unreliable for the typical severe/profound loss. Ed

#5

One of the reasons I wanted to post the recruitment thread was due to my high frequency hearing loss. Others may have similar situations.

Ed, I also believe you are correct about the audio gram results. With false interpretations of hearing levels in the higher frequencies it is a set up for failure concerning the initial tuning of the aids.

I have found that when the aids are pushed, gain wise, in the upper frequencies they can quickly become very loud and not understandable. This I believe is recruitment in my case. The Phonak program does not see recruitment and tunes for this high frequency loss. This in turn will blow some users out when in noisy areas. So, I have de-tuned or lowered the gain, on my aids in these upper frequencies with fantastic results.

Ed, does this sound correct?

Thanks

#6

I am only vaguely familiar with the Phonak Ipeg software. I would think that the automatic software probably inserts a modicum of compression when presented with losses above 50 db or so. If more compression and/or lowering of the knee point is required to handle recruitment, it is up to the fitter to program it in.

Yes, just sticking linear high volume hf into a big loss ear is surely going to be counterproductive. Ed

#7

Inputting ucl #s (uncomfortable levels) on the audiogram is where recruitment is addressed.
The mpo can be manually adjusted down, leaving the compression ratio lower, helping up to some level.

#8

Thanks shan, these ucl’s will do the trick for loud environments but will still allow for max controlled gain in quieter situations. Does this sound correct?

The recruitment is only controlled when needed. An upper control limit on gain. Much like tuning controls in the petrochemical field.

I was hoping this thread would help others that have similar situations. If anything, it would help them to better explain the problem to their audiologist.

Thanks

#9

This is where digital hearing aids “can” excel by being able to control the UCL and the MPO.

My sister, who has a very profound loss, has an extreme case of recruitment where there is approx. 10db difference between comfort and pain - it’s been a real challenge to get an aid to help her. Thus an experienced audie and a high end power aid is the solution to getting the settings right.

This tread has been extremely helpful to understanding the recruitment “challenge”.

Thanks Rick for starting it and all those who contributed.

#10

With regard to MPO’s (Maximum Power Output) and other output stage limiters. Most if not all of these will cause audible distortion if driven too hard too long. It all revolves around the timing of the MPO circuit. If the timing (the time it takes to activate gain reduction) is fast it will distort the signal envelope. Output gain devices are really kinda a last resort to keep short transient peak signals from reaching the UCL point.

IMO better, less distortion prone, UCL and recruitment control is usually accomplished earlier in the chain with WDRC (Wide Dynamic Range Compression). Ed

#11

The mpo can be manually adjusted down, leaving the compression ratio lower

… I think you mean higher …

My sister, who has a very profound loss, has an extreme case of recruitment where there is approx. 10db difference between comfort and pain - it’s been a real challenge to get an aid to help her. Thus an experienced audie and a high end power aid is the solution to getting the settings right.

This may be hyperacusis … which is VERY rare and may be due to nerve network damage or a brain issue, not recruitment. It is VERY difficult to fit hyperacusis cases … and even when set up properly, the resulting 10dB dynamic range won’t deliver much data to the brain. Power aids aren’t usually needed in such cases as the MPO/UCL comes DOWN at the same time as the threshold goes UP.

When the compression is adjusted properly for our ears, these hearing aids can do a remarkable job of compensating for our recruitment problems.

I regard compression as a tool to correct for the loss of outer hair cells, rather than as a method of dealing with the more general issue of recruitment.

More generally, recruitment won’t take place until the loss is around 55dBHL - 65dBHL i.e. when the inner hair cells start exhibiting damage. In reality the majority of hard of hearing have losses of 55dBHL or below - except possibly at 3KHz or above. In other words recruitment doesn’t have a major impact for most hearing aid users.

Recruitment is indeed a REAL problem … BUT … I suspect that people worry about it too much. It’s not going to be an issue for most HOH.

#12

I don’t disagree with that, inputting ucl’s on the audiogram would be doing just that. At the starting point.
English disp. I am sure you are right also. MPO being a kneepoint of compression and lowering it would raise the ratio. The relationship between G40-60-80 could be closer to normal though. I have put MPO’s, to close, to output and it is distorting.
My real life situation is that every day I will run into situations where sounds are too loud. Maybe it is only a 80-90 dbl. Short term, normal hearing can take this, I have to cover my ears or leave. Smoke alarms are 80 dB +/- at about 2500 Hz, (I know , you can get 500 Hz…) Un aided this should be a mild 25-30 db. Not the case.
I have gone the opposite route than the (everyone should be open fit) craze.
1.5 mm vent is enough. Controlling all of the sounds seems helpful to me.
What is the least amount of amplification/output required to get the most benefit… More bandwidth??? I read an article/interview a few years ago with Harvey Dillon, he suggested there was a loudness quotient , more is not better.
Ed you have really always preached this. I ramble

#13

This is a thread from a long time ago.
It may help some who have issues with pain from their hearing aids. The information is still good today as was back in 2009.

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#14

The issue I have with this recruitment concept, which is believe is more technically described as a non linear response to increasing gain, is that it is not measured. It is simply assumed that if you have hearing loss you have a certain level of non linear gain. The correction for non linear gain gets baked into the prescription formula for compression. I don’t think it is a one size fits all thing, but that is the way it gets treated. You walk in the door, get an audiogram, and then a prescription formula gets picked, probably primarily on the basis or what the fitter usually does, a proprietary one, or one of the industry standards.

The starting point of the problem is that an audiogram is based on threshold hearing, but we live in an environment way louder that our threshold level of hearing. The whole range of gain corrections is based on one single point of threshold hearing. It seems to me that there must be a better way of testing hearing for purposes of prescribing correction than the threshold method. Perhaps the future of hearing correction, is not more bells and whistles in the hearing aids, but more sophistication in the measurement method during diagnosis.

#15

Isn’t that UCL or MCL? Whatever it’s called. Entirely subjective to what you perceive as opposed to real threshold detection but it’s a part of tests that I’ve had.

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#16

That is my understanding too.

Upper comfort level is different with everyone. My wife for example will double over in pain when UCL is reached. We have members here talking about it all the time but don’t understand it as recruitment. At least that’s my understanding. The pros might correct me on this.

Very much a part in fitting aids properly.

#17

I think the synonym is hyperacusis. I believe I have a loudness sensitivity. Quick loud sharp sounds really make me jump. I see other “normal” people where they don’t jump with the same sound. For them it’s just …meh…yeah that was loud…carry on.

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#18

That may be what my wife has. Recruitment and hyperacusis have similarities. Here is a copy and paste from a quick google search.

Difference between hyperacusis and recruitment

Hyperacusis and recruitment are not related. The significant difference between the two is explained physiologically: recruitment is a problem of the peripheral auditory system, meaning the ear and the hair cells, whereas hyperacusis is a problem of the central auditory system.Jun 15, 2007

#19

I think there are three lines of defense against really loud sounds. On is just the louder sounds compression slope. Another is setting the MPO of the aids. And last some manufacturers include a transient noise reduction system. Siemens, now Signia/Rexton came out with it in 2006, and should be on your KS7’s. They call it SoundSmoothing. It has a low, medium, and high, setting, for each program. I have mine all set at high.

#20

@John_Green This article made me think of you.
Do you think this is your issue?

#21

Thanks for that Rick.
I do think recruitment is part of my problem, but probably not all. I liked your explanation. Very few people I have mentioned it to to had any idea what it was. The way I explained it was like a radio tuned to one frequency, but with the volume turned all the way up trying to hear a signal that was not on its frequency. When even a small signal on its frequency is detected, because the volume was at maximum, that signal is overpowering. Not nearly as complete, but simple enough that most people get the idea.

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