As hearing health care professionals, we sometimes have the opportunity to view the world from two additional non-self perspectives: that of the manufacturer, and that of the patient.
Manufacturers try as best they can to provide products which market research indicates is most appealing to the hearing impaired, whether or not those individuals are truly informed. After all, manufacturers who provide the most appealing product and support at the best price will likely achieve the best sales. Patients on the other hand, care most about value, convenience and having their needs met!
According to recent contributions to the literature addressing volume controls (VCs) as an option or as a standard product, it appears that a presumption has been made that once desired gain is programmed into the instrument, that's it. Done, finito, the end. But sounds and perceptions vary over time, and even the best programming and software cannot anticipate and accommodate all internal and external needs.
Contrary to the above mentioned presumption, and what appears to be popular current fitting philosophy, the human hearing system is dynamic - it changes constantly.
Comfort levels change throughout the day. Most Comfortable Loudness (MCL) results tell us that the same patient can prefer highly variable loudness levels to the same stimuli over the course of minutes, hours, days, weeks and months! We also know that loudness growth and loudness tolerance change with fluctuations in body chemistry. Listening perceptions are influenced by emotional, hormonal, and attentional factors. Then, if we add into this pool of variables: auditory deprivation, background noise, acclimatization, ambient reverberation, signal-to-noise ratios, central auditory processing disorders and other variables, we have a system whose need for periodic real-time adjustment supercedes expectations inspired by marketing or sales strategies to the contrary.
To better drive home this point in continuing education classes, this author goes through a litany of things that change dramatically in the human body as the day progresses. For example, as the day progresses from morning until night, we lose at least ½ inch to 1 inch of height. Our visual acuity also noticeably deteriorates, as does olfactory, gustatory and tactile senses. They all lose sensitivity to some degree over the course of a long day.
But more to our discussion here: Even those fortunate enough to have excellent hearing lose some 3 to 4 dB of threshold sensitivity at 1KHz by nightfall. In the hearing professions it's called auditory fatigue, or a lessening of sensitivity as the ears are bombarded with noise. Importantly, for the person with sensorineural hearing deficits, that translates into amplified noise.
The just noticeable difference (JND) lost by the normal ear translates into larger JNDs when measured on impaired ears stressed out with recruitment and loss of soft sound sensitivity.
It is no mystery, for instance, that an ear with a threshold of 60dB at 1KHz, can experience a loudness sensation almost identical to that of the normal ear by the time sound levels reach 80dB. The ear with a sensorineural hearing loss can zoom from just barely hearing, to almost uncomfortably loud hearing in a mere span of 20dB in loudness change. Of course, the normal ear enjoyed a range of 80dB to reach the same sensation level! That's a 5:1 loudness growth factor, or up to 5 JNDs of auditory fatigue and a perceptual variation greater than AGC or WDRC can practically accommodate.
There are many more reasons normal and abnormal ears change with regard to hearing sensitivity, even at threshold levels, from hour to hour and day to day. These reasons and variables present a compelling rationale for providing a user VC for every hearing aid user that can handle one - and perhaps for some of those we thought couldn't! Interestingly, some 77% of experienced users, when asked their preference, insist on a user VC1, regardless of how "automatic" their new instruments were promised to be.
Top ten lists are very popular now. However, I have eleven points to cover! Therefore, in order to further explore why VCs should be standard equipment, rather than options for those with the mental cognition and physical dexterity to handle them, here are the top eleven reasons:
- Auditory Fatigue . OK, yes. I mentioned this earlier. Nonetheless, I believe it is worthy of a little more elaboration2. Suppose you had dispensed and programmed your patient's new VC-less instrument(s) first thing this morning. By the time that all-important evening function rolls around, they will have lost a good portion of the needed gain to socially survive. Consequently, in their next post-fitting visit in the late afternoon they complain of "not hearing clearly at times" (they've not yet associated time of day with when those difficult times occur, and possibly neither have you). So, you ever so deftly program their gain setting up a couple of notches and become (momentarily) their super-hero: "Wonderful!", "That's more like it", "Wow, what a relief! My voice no longer sounds like my ears are stuffed up!" All smiles and peaches and cream....until the next morning when the birds chirp just a few JNDs louder than well-rested ears would like! A few trips of this back-and-forth "dance" to your office, and they begin carrying their "on trial" hearing aids in their hands, or worse still -in the box instead of their ears, when they see you next time..."These just aren't working out. You told me they were automatic..." Well, yes, they are automatic, but they can't adjust your neurological system...
- Variations in Eustachian Tube (ET) Dysfunction- In this author's experience, it is the rare elderly hearing aid user who does not experience at least some seasonal allergy, colds, barometric and temperature changes which may impact their perception of hearing, secondary to changes in their ET.3 The worsening of low frequency thresholds, and their own voice occlusion can generally be accommodated with a user controlled VC. Certainly, ET fluctuations do not present any constancy in the loudness domain, but they are important and significant to hearing aid users.
- Auditory adaptation, acclimatization, suppression, fatigue, and overload are common among hearing aid users, especially elderly users.4,5 All hearing aid users experience some degree or combination of these experiences. People with milder hearing losses generally experience less of these than do people with more severe losses.
- Fluctuating hearing thresholds secondary to Meniere's, ototoxicity6 or other allergic and autoimmune reactions. While the diagnosed population of those suffering hearing loss from these etiologies constitutes only a small percentage of total hearing aid users, these patients are often the most difficult to satisfy as their thresholds often fluctuate over time.
- Limbic influences in the auditory experience (i.e., aversive conditioned reflexes).7 Jastreboff and Hazell present a neurophysiological model for tinnitus and hyperacusis, complete with a definitive treatment describing aversive conditioned reflexes. Indeed, emotional perceptions affect hearing sensitivity.
- Variations in telephones .8 Probably, among the most challenging listening tasks for people who have significant hearing loss occurs while using the telephone. With proper training (with a user VC), most patients can function well using their hearing aid while going from telephone to telephone. Importantly, even those utilizing telecoils must be able to adjust the volume of the instrument to equalize gain and accommodate ever changing transmission systems. Without user-controlled VCs, most hearing aid users must remove their hearing aids or put up with resonant distortion (the point just prior to feedback onset), acoustic feedback, or suffer reduced gain (in cases of telecoils) during telephone use. Not all, but most of these problems are better and more effectively managed with VCs.
- Most Comfortable Loudness (MCL) vs Phonetically Balanced Maximum (PB-Max) levels in critical listening situations.9 It is common knowledge that PB Max is often not at the same loudness as the user's MCL. Therefore, in critical listening situations, where missing acoustic information can be critical to the listener, the absence of a user VC removes the ability to make momentary accommodations when necessary.
- Abnormal loudness growth and loudness intolerance that exceed WDRC or AGC limits.8 One of the most erroneous assumptions relative to abnormal loudness growth is that recruitment and loudness intolerance can be truly correlated with preset compression ratios, or even with staged threshold kneepoints (TK). In exceptional listening circumstances that exceed programmed settings, some users will require manual adjustment to meet comfortable listening needs. This is especially true in cases of directional microphone adjustments.
- Monaural fittings in cases where binaural is indicated. Central auditory processing is interdependently binaural in function. So that, when a patient is fitted monaurally when binaural is indicated, they will experience faster loudness growth, more loudness intolerance, and a lack of the attending/squelch abilities. In this case, one ear is being asked to do what two ears were meant to do without the benefit of loudness summation, which in a practical sense opens the "window" of hearing a notch more. The user VC, in this case, allows them to make real time adjustments when needed.
- CIC fittings and knowing what you're giving up. It is virtually impossible to include every filter, control, and option in most CICs. Patients who demand CIC instruments need to be informed that wearing an instrument that is cosmetically "invisible" that they may be giving up other advantages that may help them function better: User VC, telecoils, and various options.
- RFC results. Recently, one manufacturer had consulted with the author over how to reduce an ever rising rate returns for credit that has become directly proportioned to a rise in sales of digital models. Among observations made, the promotion of digital instruments without user VCs was the single largest constant in the equation for increased RFCs. In fact, an informal count showed RFCs without VCs several times higher than RFCs with VCs.
I believe the lack of standard VCs has contributed to the persistently high rates of RFCs in the digital and hybrid technology models8. The same statistics, however, show lower tech instruments (which predominantly feature user VCs) to be 50%-70% lower in RFCs. Additionally, I believe the lack of a VC has often removed, or at least minimized, an essential auditory rehabilitation tool from patients and their hearing health professionals.10 It is the opinion of this author that when instruments without VCs are the standard, many essential ingredients of otherwise successful auditory rehabilitation regimens get tossed aside and the opportunity to succeed with amplification is reduced.
Specifically, if we do not train hearing aid wearers in the efficacious use of a VC, they will not learn to cope with varying listening situations that occur daily. The VC-less hearing aid user is also left with either having to suffer the possibility of amplification-induced damage to their hearing, or forced to pick and choose when and where they wear their hearing aids.
On the other hand, admittedly, there are probably some 5-8% of all hearing aid wearers that cannot handle a user VC, and for whom a number of trade-offs must be made to meet their dexterity and other limitations.
It's important to understand that if uninformed and inexperienced prospective hearing aid wearers are asked if they would like to eliminate user-controlled VCs, the answer is typically "yes." Having no VC may appear to the novice to be akin to having an automatic transmission in their automobile, or like having an always-on DSL hook-up rather than a dial-up. Sounds great!
The burden of such a question on the novice sets far too many up for failure when they discover AGC and WDRC are not as "automatic" as they had hoped.
Of course, if the next question is, "Would you prefer to not wear hearing aids at all," the answer to that would also be a resounding "Yes!"
So, preferences of the uninitiated may not be as accurate or revealing as the opinions formed by those who have experienced the reality of the situation. In the latter's case, they tend to be fit to be tied without their user VC.
I believe dispensing professionals need to make user VCs the rule, not the exception. We need to teach patients how to utilize this most needed rehabilitative tool. Factory order forms should reflect the use of a VC as the default (standard) configuration - not the other way around. In doing so, we expect lower RFCs which will contribute to the continued decline in the cost of instrumentation to the dispensing professional and the hearing aid user.
Our entire industry needs to re-educate itself about the dynamicism of the human hearing system, especially as it presents in the defective ear. Our patients will then enjoy the best of both worlds: the most advanced amplification technology in history, and good ol' fashioned user repair strategies when more on-the-spot adjustments are needed than new fangled technology can deliver.
Dr. Chartrand serves as director of research at DigiCare Hearing Research & Rehabilitation, P.O. Box 706, Rye, CO 81069, contact: www.digicare.org.