In a memorable scene from 'Alice's Adventures in Wonderland' the Knave of Hearts is on trial for the theft of tarts. The King of Hearts asks the jury for its verdict, but the Queen of Hearts objects. 'No, no!' she says, 'Sentence first - verdict afterwards.'
In the arena of binaural hearing aids, many audiologists echo the stance of the irascible Queen. Sentence first - (two aids for everyone!) Verdict afterwards (Are two aids really better than one for this patient?).
During the past decade, two lines of research have converged to suggest that there is no single amplification solution appropriate for every person with bilateral hearing loss.
On one hand, there is a growing body of literature on the phenomena of auditory deprivation and acclimatization (Silverman & Silman, 1990; Silman, et al.,1992; Gatehouse, 1992; Hurley, 1993; Gelfand, 1995; ) indicating that, over time, the unaided ear of a monaurally fitted individual may lose functional capacity in comparison with the aided ear. The inescapable conclusion is that, all other things being equal, both ears should be aided at the earliest sign of auditory handicap. But 'all other things' are not always equal.
On the other hand, the literature on binaural interference (Jerger, et al., 1993; Hurley, 1993; Silman, 1995) suggests that, for reasons of either prolonged deprivation, age-related changes in the auditory system, or both, some individuals develop substantial interaural asymmetries in dichotic listening to speech (Jerger et al., 1990; Jerger & Jordan, 1992; Jerger et al., 1994; Jerger et al., 1995). Indeed, one ear may even 'interfere' with, or suppress, the other ear. And this ear (the one which causes the interference) is usually the left ear.
In these individuals, it may prove more useful to amplify only the right ear. In still other individuals conventional hearing aids may be less helpful in daily living than an assistive listening device. We are faced, then, with a dilemma. Do we aid both ears in order to prevent the effects of prolonged deprivation? Do we bow to the effects of aging and avoid amplifying an ear which may actually interfere with successful communication? Or do we resort to an assistive listening device? To me, the answer is clear. It is the audiologist's responsibility to determine what form of intervention is most appropriate for each individual patient.
This cannot be achieved by the blanket application of slogans and simplistic solutions based on the assumption that all hearing-impaired persons are alike. Rather, it can only be accomplished by careful assessment of the auditory capabilities of that particular patient.
How should such assessment be carried out?
Certainly not in the time-honored tradition of PB word lists. Before we can move forward in this area we are going to have to agree to retire the traditional, and now largely discredited, approach of testing 'word discrimination'. We need to take an entirely fresh approach to the problem; an approach based on modern concepts of 'ecological validity'.
In other words, if the testing procedure is meant to predict successful communication in everyday living, then the testing procedure must be in some way related to the listening problems encountered in everyday living. It remains to be shown, for example, that the ability to differentiate among nonsense syllables has relevance for understanding continuous speech from one direction in the presence of background noise from another direction.
It seems clear to me that techniques for evaluating the ability to understand speech via amplification should have at least the following characteristics:
The ultimate recommendation should be based on a comparison among the results observed in these various conditions. Usually performance will be best in the both-ears-aided condition, and this will justify a binaural recommendation.
But it may very well be the case, especially in elderly persons, that performance is at least as good, if not better, when only one ear is aided, or when an assistive listening device is included in the evaluation.
The patient deserves, and the audiologist ought to require this information before specific amplification recommendations and purchases are made.
After you have talked to audiologists for as many years as I have, you learn to anticipate two eternally predictable responses: 'I cannot possible spare the time to do all of that testing', and, 'Why bother with all that testing. I just let the patient decide what he/she likes best'.
My reply is simply this. Make every effort to find the time! Because the hallmark of an audiologist is the extent to which the solution to the patient's hearing problem is based on quantifiable data derived from sound, scientifically valid principles, rather than the principle of least effort. Accountability demands no less from us.
It is not the purpose of this paper to recommend a specific test or combination of tests. There are many pre-recorded test procedures commercially available that can be adapted to meet the recommendations listed above. Those who find none of these procedures to their liking are encouraged to develop their own techniques.
The important thing is not which test you use, but how you do the testing. Begin with a firm determination to break from the past and do the testing properly instead of the way it has always been done. Gather up all your word lists and consign them to the flames. Resolve to bring the fresh light of a new dawn to hearing aid evaluation.
For most hearing aid users a binaural fitting is usually the best choice. Indeed, it is important for preventing the effects of auditory deprivation on an unaided ear. But some individuals, especially in the elderly population, may actuallydo better with a different arrangement.
It is the audiologist's responsibility to determine, quantitatively, what system of amplification is optimal for a particular patient. To do this the audiologist must evaluate hearing aid performance using modern techniques that are ecologically valid for predicting success in daily living.
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Gatehouse S. (1992). The timecourse and magnitude of perceptual acclimatization to frequency responses: evidence from monaural fitting of hearing aids. Acoust Soc Amer 92 :1258-1268.
Gelfand, S. (1995). Long-term recovery and no recovery from the auditory deprivation effect with binaural amplification: six cases. J Amer Acad Audiol 6:141-149.
Hurley RM. (1993). Monaural ear effect: case presentations. J Amer Acad Audiology 4: 285-295.
Jerger J, Stach B, Johnson K, Loiselle L, Jerger S. (1990). Patterns of abnormality in dichotic listening. In: Jensen J, ed. Presbyacusis and other age related aspects. Copenhagen: Stougaard Jensen.
Jerger J, Jordan C. (1992). Age-related asymmetry on a cued-listening task. Ear
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Jerger J, Silman S, Lew HL, Chmiel R. (1993). Case studies in binaural interference: converging evidence from behavioral and electrophysiologic measures. J Amer Acad Audiol 4: 122-131.
Jerger J, Chmiel R, Allen J, Wilson A. (1994). Effects of age and gender on dichotic sentence identification. Ear Hear 15: 274-286.
Jerger J, Alford B, Lew H, Rivera V, Chmiel R. (1995). Dichotic listening, event-related potentials, and interhemispheric transfer in the elderly. Ear Hear 16:482-498.
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This article originally appeared on www.audiologyjournal.com. Audiology Online (www.audiologyonline.com) has acquired the Audiology Journal. This paper has been re-edited and updated and appears here as a courtesy to our readers for educational and informational purposes. We are grateful to the author and to Audiology Journal for allowing us (Audiology Online) to re-publish this updated version of this article here. Respectfully, Douglas L. Beck Au.D. Editor-In-Chief, Audiology Online.
