Self-Fitting of Hearing Devices – Part I

Self-fitting of hearing devices is an inherent feature of OTC or DTC (over-the-counter; direct-to-consumer) hearing aids.  What can we expect now that this is becoming an active feature of hearing aid sales?

The real issue, as expressed by Bess¹, is not how an OTC or DTC hearing aid delivery system benefits hearing aid manufacturers and hearing professionals, but will this benefit those with hearing loss?  The OTC option is intended to provide greater access for individuals to use amplification than does the current model of hearing aid distribution.  Without a doubt, the current distribution system would not be able to manage the influx of sales if the intended goal is to substantially increase the number of individuals using amplification.²   With this in mind, some have been concerned that OTC (over-the-counter) sales, which essentially includes self-fitting of hearing aids, cannot be managed effectively by the consumer.

Self-Fitting Defined

What is a self-fitted hearing device?

The essence of self-fitting is that the assembly, fitting and usage of hearing aids is completed by the user without any hearing experts and equipment, other than the hearing aid.

In this series of posts that will follow, as related to OTC sales, PSAPs (Personal Sound Amplification Products) are considered to be the same as OTC hearing aids, which they are, regardless of how some chose to nit-pick definitions.

The definition above of self-fitting is different than what some have suggested, such as:

“A self-contained, self-fitting hearing aid (SFHA) is a device that enables the user to perform both threshold measurements leading to a prescribed hearing aid setting and fine-tuning, without the need for audiological support or access to other equipment.”³

This author prefers the initial definition of self-fitting and has problems with this latter definition, and for other similar definitions that suggest the need for audiometric data for a self-fitted device, for the following reasons:

• There is no need to have a measurement of one’s hearing thresholds. This has been explained in a previous post.  For the most part, there is little difference in the threshold configuration of most mild and moderate hearing losses, other than the sensitivity level and minor changes in the high-end response, much of which can be managed easily with a user-adjustable volume control, and a couple of push-button response changes, if that is even desired.

• The FIRST, and PRIMARY decision that all hearing aid users make is if the instrument has sufficient gain. Is it proving enough amplification so that they can hear others/things better than without amplification, and to their satisfaction.  Knowing this, give the customers a user-controlled gain option.  After all, they can make a better decision as to what gain they will accept than can an external evaluator or fitting formula.^4,5   As to the significance of frequency response adjustment, few users can tell the difference in frequency response unless it is dramatic – more dramatic than the environmental differences often programmed into hearing aids today.  Anecdotal evidence can easily be obtained by asking customers if they can tell the difference between the various environmental settings.  To most, they sound the same, with the exception of a loudness reduction when the directional microphone performance is chosen (generally, listening in noise).

• To use hearing thresholds to lead to a prescribed hearing aid setting is no guarantee of a successful hearing aid fitting because of the great variability in target gains projected by different hearing aid formulae.^6,7,8,9,10 As reported previously, Hearing instrument manufacturers’ first-fit algorithms are known to deviate significantly from actual prescriptive targets.^8,10   Aazh and Moore found that using first-fit, 64% of hearing instruments failed to come within +/- 10 dB of target at one or more frequencies.  Similar results were found for open-fit hearing aids.¹⁰

• Hearing thresholds have little or nothing to do with fine tuning of a listening device. Fine tuning is generally performed by changes to target gains based on subjective responses by the hearing aid user, not on audiometric thresholds.  Adjustments are generally made by using the program’s “Fitting Wizard” (which is a calculated guess), or best, by adjustment using real-ear measurements.  Unfortunately, few audiologists actually use real-ear measurements, even though many have the equipment in their offices.^{11,12,13,14,15}    In a survey of dispensers, 57% reported owning real-ear equipment, but only 34% (considered an inflated percent, and perhaps closer to 25%¹⁶) of all respondents who reported that they used the equipment consistently, even though it is considered a major part of Best Practice.¹³    

The suggestion that a measurement of hearing threshold is required is without doubt, the single greatest artificial/intentional roadblock to self-fitting of hearing aids.   

What is Available for Self-Fitting?

An excellent review of partial self-fitting without audiological support has been published by Keidser and Convery.²  The devices identified in the reviews of that publication universally required access to other hardware, such as a proprietary interface, computer, smartphone, or tablet to enact the fitting.  None of such devices would be considered a “self-contained” or “self-fit” hearing aid by this author because they rely on some additional hardware/interface. 

Because certain approaches employ additional hardware does not make them poor options for self-fitting in and of themselves, but a true self-fit device should be something that any person can use, regardless of where in the world they live.  And, to really meet the unserved market, it should not require an additional device that many customers do not nor will not have access to, or perhaps cannot manage.  What if they have no cell phone service, can’t afford a computer, smart phone, or tablet?  A truly self-fitting device should require nothing more than the product itself, along with easily understood instructions on its use.

Are Any Such Self-Fitting Hearing Aids Available?   

Fortunately, current devices now exist that can be considered fully self-fitting without audiological support, assuming that one ignores the unnecessary “requirement” that an audiogram is necessary.  The Bean by Etymotic Research, the Tweak by Ear Technology, and the CS50+ by Sound World Solutions are such devices, as are essentially most PSAPs.  If any of these devices also connect wirelessly with a smart phone or with providers that offer assistance through a telehealth infrastructure or integration into a traditional hearing health-care model, that is good.  But, it is not a necessary requirement for self-fit because most (not all) of such connections are designed to obtain or use some kind of audiogram, thinking this is necessary because it has been suggested by hearing professionals.  The attempt at obtaining an audiogram is fraught with regulation and calibration issues that are best left to traditional hearing aid fitting, where it is believed that an audiogram is necessary to fit a hearing aid. 

Predicting Hearing Level Without an Audiogram

Can this be done?  It is suspected that most hearing professionals make such a prediction prior to taking an audiogram, by just talking with the customer.  It has been suggested that such a prediction could be made just using a proper questionnaire.

At least one self-assessment questionnaire has been shown to provide valuable information about an individual’s hearing levels without resorting to a pure-tone audiogram.  For example, the following comments were made relative to an inquiry made to the authors of the NSRT test, asking how well their questionnaire items related to measurements of hearing levels by category of loss.  The NSRT test was questioned because it is one of the few that has good statistical data associated with it.  The response was as follows:

“You asked how well the questionnaire items relate to the “final estimate of hearing levels by category”, as well as “general hearing level”.  Simply put, the six Likert items to which respondents provide data entries conspire very nicely to form an independent measure of hearing sensitivity (KR₂₀ = .92).  Simple-sum scores on the questionnaire separate respondents into four HL groups (normal, mild loss, moderate loss, severe loss).  I was quite surprised to see how well respondents separate into categories based upon hearing loss (predicted PTA) simply using the questionnaire data.”¹⁷

If the purpose of a self-fit hearing aid is to get individuals who have mild-to-moderate hearing loss, and who take no amplification action because of the various hoops required of them to go through, along with unacceptable/unaffordable costs, it would appear that the drive to action should have as few obstacles as necessary.  And, the big elephant obstacle in the room relates to the audiogram.

Self-fitting of hearing aids will continue in next week’s post.

References

1. Bess F. (2004).  Vanderbilt University, Fred Bess Ethics Class, November 28, 2004, Memphis, TN.
2. Marquardt K, Hosford-Dunn H, Fishback P. (2017).  The supply and demand for audiologists: preliminary modeling and analyses.  https://hearinghealthmatters.org/journalresearchposters/files/2017/06/Supply-and-Demand-for-Audiologists-Preliminary-Modeling-and-Analyses.pdf.
3. Keidser G. and Convery E. (2016). Self-fitting hearing aids: status quo and future predictions.  Trends in Hearing, Vol. 20, 1-15, April.
4. Killion M. (2004). Myths about hearing aid benefit and satisfaction. The Hearing Review, August, pp 14, 16, 18-20, 66.
5. Keidser G, Brew C, Peck A. (2003). Proprietary fitting algorithms compared with one another and with generic formulas.  Hearing Journal. 56(3):28, 32-38.
6. Hawkins D. and Cook J. (2003). Hearing aid software predictive gain values: how accurate are they?  The Hearing Journal. July, Vol. 56, No 7, pp 26, 28, 32, 34.
7. Aarts, N., Cafee, C. (2005). Manufacturer predicted and measured REAR values in adult hearing aid fitting: accuracy and clinical usefulness. Int. J. Audiol. 44, 293-301.
8. Azah H. and Moore BCJ. (2007). The value of routine real ear measurement of the gain of digital hearing aids.  Journal of the American Academy of Audiology, 18(8), 653-664.
9. Sanders, J., Stoody, T., Weber, J., Mueller, H.G., 2015. Manufacturers’ NALNL2 fittings fail real-ear verification. Rev. 21 (3), 24.
10. Azah H, Moore BC, & Prasher D. (2012). The accuracy of matching target insertion gains with open-fit hearing aids. American Journal of Audiology, 21:175-180.
11. Beyer C. (2011). Common mistakes in routine hearing aid fitting.  https://www.audiologyonline.com/ask-the-experts/common-mistakes-in-routine-hearing-39.
12. Kirkwood D. (2006) Survey: Dispensers fitted more hearing aids in 2005 at higher prices. Hear J 59:40–50.
13. Bamford, J., Beresford, D., Mencher, G., 2001. Provision and fitting of new technology hearing aids: implications from a survey of some “good practice services” in UK and USA. In: Seewald, R.C., Gravel, J.S. (Eds.), A Sound Foundation through Early Amplification: Proceedings of an International Conference. Phonak AG, Stafa, Switzerland, pp. 213-219.
14. Mueller HG, Picou EM. (2010). Survey examines popularity of real-ear probe-microphone measures. Hear Jour. 2010;63(5):27-28.
15. Mueller HG. Probe-mic measures: Hearing aid fitting’s most neglected element. Hear Jour. 2005;57(10): 33-41.
16. Mueller HG. 20Q: Real-ear probe-microphone measures—30 years of progress? AudiologyOnline, Article 12410 [Jan 2014].
17. Garrison W. and Bochner J. (2017).  Personal communication in reference to the NTID (National Technical Institute for the Deaf) NSRT Speech Recognition Test.