I have long known about the research of Dr. Brian Moore, specifically about his work with dead regions in the cochlea. I have even purchased and used the TENS test to determine whether or not a region was healthy enough to receive amplified sound. “Cochlear dead regions” is a phrase that refers to a very significant amount of damage to the inner hair cells in the cochlea such that amplification with hearing aids may not be a good thing. This is a case where less may be more.
Academically I know about “cochlear dead regions” and have even spoken about them; the literature has been discussing this issue for more than a decade. But only recently have I begun to really use that knowledge. In the past it was almost as if I was being macho and felt that the more gain I could give my clients at 4000 Hz (the top note on the piano keyboard), the better job I was doing. And, of course, I “knew” my clients would hear better- never mind that that was not always the case. After all, as a macho audiologist, I knew better.
Back then, I felt, “cochlear dead regions” was a subject better left to the ivory towers of universities, and if my clients couldn’t use the amplification I gave them, that was their problem!
Of course, I am being tongue in cheek. In the vast majority of hearing aid fittings, because of the limitations of modern hearing aid technology and the severity of a person’s high-frequency hearing loss, insertion gain measures would generally fall short of the “target” gain at 4000 Hz. It is a rare situation where I can actually achieve the desired gain at 4000 Hz in any event, so why worry about specifying less gain?
Clinically I would do everything to enhance the amount of amplification in the higher frequency region- I would program the hearing aid to generate that gain. I would use acoustic plumbing to ensure that the earmold coupling was as optimal- I even referred to myself as a “dB squeezer”- someone who got those last few dBs out of a hearing aid fitting, like squeezing the last bit of toothpaste from the tube.
But back to “cochlear dead regions”. Once a cochlear dead region is suspected, the clinical approach is to stay away from that frequency region. One would typically reduce the amount of amplification in that frequency region(s) or perhaps use frequency transposition to shift the effective amplification to a lower (and hopefully) healthier cochlear region. But even though I knew that intellectually, it wasn’t until recently, when I started to use my clinic piano, that it was driven home. The piano is now part of my clinical armament- almost as useful as my audiometer.
Here’s how it works. I have my hard of hearing clients (with or without their hearing aids) sit down and start playing the notes sequentially from about 1000 Hz and up … white key, black key, white key. One thousand Hz is about two octaves above the middle of the piano keyboard and about half way between the middle (near 250 Hz) and the top note (4000 Hz). I ask clients to tell me when they can no longer distinguish between two adjacent notes. For example, they may find that starting around G, that G and G# sound about the same pitch. This corresponds to 1500 Hz (or perhaps 3000 Hz if it’s in the top octave of the piano). This is an area that I want to stay away from.
The following table gives some “approximate” frequencies and their corresponding musical notes starting at middle C (the middle of the piano keyboard):
Of course, middle C is not 250 Hz; it is 262 Hz, and the top note on the piano keyboard C is not 4000 Hz; it is 4186 Hz, but the numbers in the table are close enough. This takes about 15-20 seconds and gives clients a sense of being involved in their hearing rehabilitation. Interestingly enough, this corresponds well with the results of Dr. Moore’s TENS test- actually not so surprising since this is really just another way of assessing the same phenomenon. A comparison of Dr. Moore’s TENS test and this adjacent piano note test would make an interesting Capstone project for some AuD student.
I saw two hard of hearing musicians earlier in the week whom I have been seeing for at least 1000 years. They had complained about “fuzziness” despite my best macho audiology tactics. After this brief piano test, I reduced the gain above 2000 Hz in one ear (and bilaterally for the other musician) and the fuzziness went away. I had to explain that I knew about this for the past decade but was too clinically pig-headed to do anything about it!
Although I have not done a statistically valid survey of audiology clinics, I suspect that most clinics do not have a piano in their office. However, this is not an issue of pitch perception or even one of “just noticeable difference”. It is a simple issue of “same” or “different”.
A $25 Cassio 1970s kid’s piano keyboard would do the trick, and you can still find them for sale at low-end electronics stores or at many garage sales. Pull out the portable keyboard, ignore its tuning, and just go to work. Are two adjacent notes the “same” or “different” is all we need to know. If two adjacent notes are the same, then minimize the amount of hearing aid amplification in that region.