Dr. Ross on Hearing Loss
Reflections on Binaural Hearing Aid Fittings
by Mark Ross, Ph.D.
When it was first suggested to me that I write on this topic, my first thought was "what again!" Twenty years ago, when I reviewed the literature on binaural/monaural hearing aids (Ross, l977), I thought the conclusions were pretty clear - and I still do: most people with hearing loss, in most situations, are going to hear better with two rather than one hearing aid. So why is this issue still with us? Why doesn't just about everybody with a bilateral hearing loss wear binaural hearing aids? Although some of the old reasons no longer apply in this day and age, a little historical background can give us some perspective in understanding the answers to these questions.
In the (Almost) Beginning
When people first started wearing hearing aids, it was just about physically impossible to wear two of them because of their size. The salient question then was not whether two was better than one, but rather could the person derive any benefit at all from a hearing aid? If this sounds too simplistic, we should recall that it wasn't all that long ago when many physicians (in particular) believed that if you had a sensori-neural hearing loss, you couldn't be helped with a hearing aid. It took a long time for the realization to germinate that people with sensori-neural hearing losses were indeed potential hearing aid candidates. This in itself was a revolutionary idea, never mind thinking about an aid for the other ear! When I put on my first body worn hearing aid 48 years ago, it never occurred to me, or to anybody else as far as I could tell, to think about a binaural fitting. It just wasn't done. But I'm sure that I (and just about every other hearing aid user I knew in those days) would have resisted the idea of a binaural body aid fitting, regardless of any possible acoustic advantages.
The normal recommendation, then, was for one hearing aid. Many articles on fitting hearing aids (including some of my own) focused on which ear to fit. So we developed such rules as "fit the worse ear, when the better ear can make an unaided contribution", unless "the speech discrimination in the worse ear is "x" amount (never really defined) poorer than the better ear", and so on. Some of us would recommend an earmold for each ear, so that the aids could be switched from ear to ear (to keep a non-aided ear from getting "rusty" - sound familiar?), or a "Y" cord, particularly for children when we didn't have accurate individual ear information.
Advent of Ear-Level Hearing Aids
This orientation carried over when ear-level aids were first developed in the late l950's. Although hearing aids had changed, we hadn't. Because one hearing aid was the norm, it became necessary to prove that two was better than one in order to justify the second aid. The burden of proof, in other words, fell on the binaural advocates. We (and I number myself among them) had to prove binaural superiority, and we had to do it in "objective" and "scientific" terms. Just taking hard of hearing people at their word, no matter how similar their unsolicited descriptions of binaural superiority were, was not enough. There was a great divergence in attitudes between hearing aid dealers and audiologists (who were forbidden at that time from selling hearing aids). The dealers were saying binaural was really better and we were saying they were being influenced by the extra sale (not necessarily mutually contradictory points!). We demanded proof, in terms that a new, insecure, and somewhat skeptical profession could accept (i.e. data-based studies).
First Research Studies
The first studies comparing binaural/monaural hearing aid performances were done in the late l950's. By today's standards, these would be considered woefully inadequate (e.g., body aids mounted adjacent to ears for the binaural condition and on the chest for the monaural condition, or testing speech discrimination only in quiet). Later studies in the l960's and 70's were more sophisticated, although not always very realistic. For example, in a common paradigm, the stimuli was recorded through a stationary KEMAR (an artificial head) in an effort to control for head movements; however, since one of the factors underlying normal binaural listening is precisely slight head movements, the study's design eliminated one of the salient factors distinguishing binaural from monaural listening.
And then we had years of research in which the primary signal was delivered at a 45 degree angle, while competing signals were presented at the opposite 45 degree angle (the monaural direct/indirect or near ear/far ear conditions). As a hearing aid user I know that I practically break my neck at times to ensure that I can face the person I'm listening to (a zero degree azimuth condition for the primary signal). Don't we teach our patients to face the person who is doing the talking? When was the last time you faced straight ahead while you were listening to somebody at a 45 degree angle from you? In other words, many of these studies were a bit weak on face validity. Still, of the 19 studies completed by l977, none showed monaural superiority (4 were equal and 15 favored the binaural condition). But even while these studies were going on, and there was still a professional dispute about the merits of binaural listening (the hearing aid dealers had no such doubts), many of us in clinics were fitting binaural body aids to congenitally hearing-impaired children.
Early Binaural Fittings: The developing rationale
We took this step basically in response to the Maternal Rubella epidemic of l964 and 1965. Suddenly, we were faced with a horde of hearing-impaired children in our clinics who we had to manage as well as we could, giving them the benefit of any doubts regarding the merits of binaural amplification. In doing this, we were also stimulated by the early "True Believers" in the auditory approach, basically inspired teachers of the deaf (Helen Beebe, Ciwa Griffith, Doreen Pollack, Marion Ernst, Ruth Bender) who pushed the nascent profession of Audiology to be more aggressive in our auditory treatment for these children. They had no hard data, just their refined clinical observational skills, and sometimes they pushed when it was inappropriate (e.g., expecting totally deaf children to "listen"), but basically they set up a challenge that audiologists felt compelled to respond to. While I don't have any specific figures, my impression is that some large portion of these early rubella children were fit with body worn binaural aids, supported mainly by our observations of the children's auditory-verbal development rather than their responses to speech discrimination tests. Young profoundly hearing-impaired children, as Gus Mueller and Allison Grimes discovered in their l977 study of monaural/binaural performance, are not the most suitable subjects for word recognition tests.
With adults, on the other hand, the usual binaural/monaural evaluation procedure depended upon demonstrating binaural superiority in speech discrimination scores. While such word discrimination tests can be appropriate measurement tools, the common clinical practice was to deliver the speech stimuli with monitored live-voice, using no more than 50 words, without realistic test conditions (i.e., frontal location of primary signal, appropriately located competing noises, and at several intensity and signal to noise levels). Given these kinds of unstandardized and unrealistic assessment conditions, the wonder was that binaural superiority was so often demonstrated in the test scores! Adults with hearing loss were telling us that it was "easier" to hear with two aids than with one (less effort, shortened latency time), that they experienced a sense of "fullness" and "space" with two aids, that it was easier to localize the source of sound (this observation had been supported in the early research), and that they could hear people on either side of them. We didn't know what to make of these observations, since relevant tests for these dimensions were not part of our usual clinical armamentarium. In other words, there were (and are) perceptual differences between binaural and monaural hearing aid use that were (and are) difficult to evaluate, and for too many of us if it couldn't be measured, it wasn't relevant.
"Assertive" Binaural Fittings and "Auditory Training"
But let's jump ahead 20 years from the time I wrote the chapter I referred to above, to the current year l997. What's different now? Well, for one I don't think we'd find many audiologists who would deny that normally, binaural listening is superior to monaural for most people with hearing loss. This is one issue that I think we have finally resolved. "Hearing aid fitting" should normally mean binaural in the same way that fitting eyeglasses implies a stereoscopic fitting. Of course, we still have to determine exceptions for particular individuals and here I think that we're often much too cautious. A person doesn't have to show a symmetrical hearing loss in order to benefit from a binaural fitting. Other than the person with absolutely no hearing in the contralateral ear, I'm not sure who I would disqualify as a potential binaural candidate. The question I would ask - at least initially - is not whether it can be objectively and subjectively demonstrated that binaural aids are superior to a monaural aid, but is objective and subjective performance poorer with two rather than one aid. If not, then it's worth giving the binaural fitting an intensive and supervised trial. There is nowhere else to go but up.
In the past, I've recommended many binaural hearing aids for people with very asymmetrical hearing loss, like a flat loss in one ear and a corner audiogram in the other. My rationale was the demonstrated capacity of the central auditory system to fuse disparate simultaneous signals coming from the two ears (like a high pass filter in one ear and a low-pass in the other ear). . People with normal central auditory systems were (and presumably still are) able to do this with little difficulty and there was no a priori reason for assuming that the vast majority of hard of hearing people couldn't do the same. Yes, I know there are people with central auditory system pathologies who clearly do find that a second hearing aid diminishes their overall auditory performance. But even with them, as long as the patient is cooperative, I would suggest a careful trial period. My point is that we shouldn't write off a second ear too casually. I seriously object to using relatively rare pathological conditions to create the general impression that binaural interference is the rule rather than the exception.
The vast majority of our problematical binaural candidates are going to be those with asymmetrical hearing losses. Do we give up or do we try the second aid? Isn't auditory training something that we ought to be doing? In instances where the second aid appears to be worsening overall speech perception, I suggest that this is exactly what we should be doing. One procedure I've used is to instruct questionable binaural candidates to add the second aid in the poorer ear while watching TV commercials (of which there is no lack) or a news broadcast. I suggest that they do this for as many minutes per day as they feel comfortable, for as many days as they can tolerate, being sure to periodically switch the poorer side off so that they can compare the two auditory experiences. It may take some people longer than the typical 30 day trial period to determine whether they can benefit from a second aid, which is one of the reasons for position papers by SHHH recommending a 60 day trial period and a group hearing aid orientation program. These provisions will provide the time (60 days) and the structure (group hearing aid orientation) to help determine the efficacy of a second hearing aid (there are additional reasons, of course, for these position papers).
Cosmetics and Cost
Thanks to Shlomo Silman and Stanley Gelfand, we've had lots of attention paid lately to the phenomenon of adult onset sensory deprivation. We're pretty sure by now that it is a real event. What goes unsaid is that every time we see someone like this, somebody missed the boat (either the hearing aid dispenser or the patient, if he or she was informed of the possible consequences and elected to go with one hearing aid anyway). Before we too easily condemn hard of hearing people for not acting in their own self-interest, we should look at ourselves first. From the time I entered the field, the hearing aid industry and professionals have exhibited a schizophrenic attitude toward marketing hearing aids. On the one hand we've extolled their virtues ("get back in touch", "stay tuned to the world", "hear your grandchildren", etc.), and on the other hand, we've reinforced the stigma effect by emphasizing how invisible the aids are. What this latter kind of appeal does, in my opinion, is to simply foster denial. If a hearing loss is nothing to be ashamed of, why do we have to hide the hearing aids?
I'm not questioning the acoustic advantages of CIC aids, or the fact that for many people if the aids aren't invisible, they're not going to wear them. What I am saying - at least in this context - is that if we keep on conveying the message that a hearing loss is something to be ashamed of and a hearing aid is something to hide, then for some people the thought of using two aids conveys twice as much stigma and shame. How often have we heard someone resist accepting a second aid by saying "Oh my hearing loss is not that bad!" I can't think of any other disabilities, other than hearing loss, in which the prerequisite for an effective rehabilitation program is not the acceptance of the condition. Only with hearing loss are we expected to engage in a remediation program (and that is what hearing aids are) without the affected party acknowledging, or at least accepting, the condition we're working on. Not a very healthy situation.
And then there's money. Generally, two aids cost twice as much as one. We all know this, but we also tend to minimize it when talking to patients ("How can you put a price on better hearing? It's priceless"). No it's not. For far too many people, the "pricelessness" aspect is overshadowed by the price. Nowadays when a single hearing aid may cost several thousand dollars, we're deluding ourselves if we think the cost of a second aid does not seriously impact on people's decision to go binaural. They have to make a cost/benefit decision, and if the cost of a second aid is several thousand dollars, many are going to feel that they'll be able to "get along" with just one. I've had people call me in tears after being told by their hearing aid dispenser that their new aids were going to cost them three or four thousand dollars. While I don't claim to have an answer to this dilemma, I do think that we should acknowledge this reality and not thoughtlessly put the onus on patients (as I've heard and read) who we accuse of having distorted value systems when they reject a second aid (and walk out of the office into their new Cadillac, etc.).
The Next Step: "Trinaural" Hearing
Now that I've fulminated on the cost of binaural hearings aids, it's going to seem odd when I suggest that in the future we consider "trinaural" fittings. By a "trinaural" fitting (I know our species is not capable of trinaural hearing, but isn't it a catchy marketing term!), I mean for the hard of hearing person to have a remote microphone/transmitter available that can be placed close to the source of sounds. This is perfectly feasible now using BTE/FM hearing aids. These devices are not just for children in schools. As a matter of fact, I think the greatest market for them in the future will be with adults. Unlike conventional FM systems, both the receivers and the transmitters are convenient to wear and to use (a major reason for their lack of acceptance now by adults, as was pointed out in a recent article by Jerger, Chmiel, Florin, Pirozzolo & Wilson, l996). The newer BTE/FM systems are more flexible and adaptable than previous models. The receivers include such features as easily varied channels, squelch circuits, "T" coils, and the selection of either FM alone, microphone alone, or both. Some FM receivers are contained in boots that fit over the bottom of advanced models BTE aids. The lavaliere microphone transmitter is about the same size as the remote control in many current programmable hearing aids. Unlike these aids, however, the remote ear can directly increase the speech to noise ratio by being placed close to desired sound sources. I've experienced many occasions in the last few years where communication in restaurants, receptions, automobiles, noisy streets, etc would have been much more difficult, if not impossible, without my "third" ear.
What I'm suggesting is that binaural is not enough, at least in many situations for many people with hearing loss; with two bad ears, it's nice to have a "portable" third ear available. But while we're waiting for another generation to pass before this concept becomes widely accepted (and I hope I'm being overly pessimistic), we should, to quote what I wrote 20 years ago: "now consider binaural amplification the method of choice for all hearing impaired individuals and then modify this is specific instances in accordance with our observations, tests, and the evidence."
Jerger, J., Chmiel, R., Florin, E., Pirozzolo, R. & Wilson, N. (l996). Comparison of Conventional Amplification and an Assistive Listening Device in Elderly Persons. Ear and Hearing, 17, 490-504.
Ross, M. (l977). Binaural Versus Monaural Hearing Aid Amplification for Hearing Impaired Individuals. In, Childhood Deafness: Causation, Assessment, & Management, Bess, F. (Ed.), Grune and Stratton: New York
Ross, M. (l980). Binaural Versus Monaural Hearing Aid Amplification for Hearing Impaired Individuals. In, Binaural Amplification Volume II, Libby, E.R. (Ed), Zenetron: New York.