The MarkeTrak VI follow-up article, Isolating the Impact of the Volume Control on Customer Satisfaction, by Sergei Kochkin1 points out one of the glaring shortcomings in our current fitting strategy. The article represents an admirable and scholarly effort to bring to the surface an issue that has been somewhat suppressed as we stretch toward the Utopian Age in amplification.
Obviously, those of us in the research and education portion of the field have fallen asleep at the (volume) wheel on this one. The neglect in retaining the rightful and needed place of the lowly volume control in the dispensing regimen, in my opinion, is much like the proverbial elephant in the living room: its so obvious that, although we keep stubbing toes, we fail to see the immensity of our oversight.
By nearly all accounts in the literature relative to whether a user-adjustable volume control is an option or a necessity, it has been presupposed that the defective hearing system is a static not dynamic and changing entity, or that ones hearing threshold actually remains constant from day to day, and from morning to night.
It is not constant.2 This fact shouldnt surprise anyone: its been proven were not as tall at night as we are in the morning (eg, our body/spine sags by as much as one inch), nor is our vision or other senses as acute. Even a normal-hearing individual experiences an end-of-day auditory loss of hearing sensitivity due to fatigue of at least 1 JND (just noticeable difference, eg, 3-4 dB @ 1 kHz). In the case of the hearing-impaired person with severe recruitment, that 1 JND could be the functional equivalent of several JNDs for a normal-hearing person. And, of course, AGC and WDRC have nothing to do with maintaining MCL throughout the dayor even from day to day.
Moreover, if we were to program the gain of a VC-less instrument in the morning, by nightfall our patient might complain of dullness (need for more gain), fullness (own voice occlusion), or that the instrument is not loud enough.3 So, lets say we instead program the VC-less instrument in the evening; by the next morning, the birds will be chirping a lot louder than the clients liking. Back and forth we go, striving mightily to avoid the one thing (user VC) by which the patient can make real-time accommodations as needed, until finally, they complain, But you told me these hearing aids were automatic. Well, yes, they do adjust external inputs automaticallythey just cant control cochlear microphonics.4
Similarly, there are good reasons why Surr et al.5 found that 77% of hearing aid consumers prefer a VC, no matter how sophisticated the automatic technology. There are also good reasons why returned hearing instruments without VCs, as a proportion, far outnumber returned instruments with VCs at the factory. Here are just a few more ignore-at-our-peril reasons why user VCs should be the rule and not the exception:
- Variations in Eustachian tube (dys)function (allergy, colds, barometric and temperature changes, etc).6
- Auditory adaptation, suppression, fatigue, and overload, which are common among hearing aid users.2,4
- Fluctuating thresholds as a result of Menieres disease or dietary ototoxicity.7
- Limbic influences in the auditory experience (ie, aversive conditioned reflexes).8
- Variations in telephone outputs, hard-wire vs cellular systems,9 as well as other types of electronic listening devices.
- MCL vs PB-Max levels in critical listening situations.10
- Abnormal loudness growth and loudness intolerance that exceed WDRC or AGC limits.9
In light of the above (and more), it is distressing to see that many manufacturers order forms are designed to promote instruments without a user VC, causing dispensing professionals to go out of their way to order instruments with VCs. This is not to say that automatic instruments are without merit; on the contrary, Kochkins data1 suggests that these devices are capable of providing high levels of customer satisfaction. But it can be argued that the recent widespread focus on VC-less hearing aids has contributed to persistent returns for credit in the digital and hybrid technology models.9 It has also taken what many consider to be an essential auditory rehabilitation tool away from both patients and their hearing care professionals.11
When uninformed prospective users are asked if they would like to do away with the VC, the answer most often will be affirmative. But, then, if asked if theyd like to dispense with wearing hearing aids altogether, the answer would likely still be in the affirmative. The burden of such a question on those not informed sets up far too many clients for failure when they discover AGC and WDRC are not as automatic or adaptable as they were led to believe.
This problem represents yet another elephant in the living room, looming large, stoically sitting between todays brilliant technological achievements and a market desperately in need of it. Dispensing professionals need to make user VCs the rule, not the exception, and teach patients how to utilize this most needed rehabilitative tool. Factory order forms should reflect the use of a VC as the default option configuration, not the other way around.
And, most important of all, our entire industry needs to re-educate itself about the dynamicism of the human hearing system, especially as it pertains to the defective ear in the real world. Hearing-impaired patients will love us for it, though they may not understand all the reasons why.
|Max Stanley Chartrand, PhD, is director of research at DigiCare Hearing Research & Rehabilitation in Rye, Colo.|
Correspondence can be addressed to HR or Max Chartrand. Chartrand is director of research at DigiCare Hearing Research & Rehabilitation, P.O. Box 706, Rye, CO 81069; email: [email protected].
1. Kochkin S. MarkeTrak VI: Isolating the impact of the volume control on customer satisfaction. Hearing Review. 2003;10(1):26-35.
2. Willott JF. Aging and the Auditory System: Anatomy, Physiology, and Psychophysics. San Diego: Singular Publishing Group, Inc; 1991:168-201
3. Chartrand MS. In vigorous defense of volume control. Hearing Professional. 2001; May-June:9-11.
4. Durrant JD, Lovrinic JH. Bases of Hearing Science. 2nd ed. Baltimore:Williams & Wilkins;1984: 248-250.
5. Surr RK, Cord MT, Walden BE. Response of hearing aid wearers to the absence of a user-operated volume control. Hear Jour. 2001;54(4):32-36.
6. Feldman AS. Acoustic impedance-admittance battery. In: Katz J, ed. Handbook of Clinical Audiology. 2nd ed. Baltimore: Williams & Wilkins;1981:356-374.
7. Chartrand MS. Video otoscopy observation & referral: The FDA Red Flags. Hearing Professional. 2003;Jan.-Feb.
8. Hazell JWP. The TRT method in practice. In: VI International Tinnitus Seminar. London: Ed Hazell Publications THC;1996:92-98.
9. Chartrand MS, Chartrand GA. The nuts & bolts in solving problem fitting cases. In: program and abstracts of International Institute for Hearing Instruments Studies 12-hour CEU course; Livonia, Mich; 2002.
10. Sandlin RE. Principles of sound field audiometry. In: Sandlin RE, ed. Hearing Instrument Science and Fitting Practices. 2nd ed. Livonia, Mich: International Institute for Hearing Instruments Studies; 1996:615-618.
11. Chartrand MS. Hearing Instrument Counseling: Practical Applications in Counseling the Hearing Impaired. Livonia, MI:International Institute for Hearing Instruments Studies;1999.