Starkey Research & Clinical Blog

Can preference for one or two hearing aids be predicted?

Noble, W. (2006). Bilateral hearing aids: A review of self-reports of benefit in comparison with unilateral fitting. International Journal of Audiology, 45(Supplement 1), S63-S71.

This editorial discusses the clinical implications of an independent research study. This editorial does not represent the opinions of the original authors.

The potential benefits of bilateral and unilateral hearing aids have been debated for years. Laboratory studies and clinical recommendations generally support the use of two hearing aids for individuals with bilateral hearing loss. Yet some field studies have produced equivocal reports. In his 2006 survey of bilateral and unilateral clinical field trials, William Noble discusses variables contributing to the lack of consensus and addresses a couple of commonly cited clinical rationales for bilateral hearing aid use. Though subject population, experimental design, degree of hearing loss and usage patterns vary from one study to another, factors emerge that help determine likelihood of success in unilateral and bilateral hearing aid fitting.

The strong predisposition for clinicians to recommend bilateral hearing aid use may be based both on laboratory findings as well as common sense. Several studies have reported advantages of binaural listening (Dillon, 2001; McArdle et al., 2012), but clinicians often support their recommendation of two hearing aids with an analogy to binocular vision.  Individuals with impaired vision no longer wear monocles (with apologies to English detectives) but instead opt for binocular corrective lenses. Noble argues that the visual analogy is not apt, partly because typical vision loss is not comparable to the typical hearing loss. Rather, vision loss that is treated by corrective lenses is most similar to a mild conductive hearing loss that is rarely treated with hearing aids. Cochlear receptor damage in sensorineural hearing loss, the most common type of hearing loss treated with hearing aids, introduces processing complexities that may not be adequately corrected by hearing aids that cannot address the auditory deficits.

Though Noble’s comments are correct, the visual analogy is presented to hearing aid patients in an effort to explain how two hearing aids allow more effective use of bilateral listening cues, much as two corrective lenses can aid binocular, stereoscopic cues for depth and three-dimensional perception.  Some patients may have difficulty understanding how two hearing aids can provide beneficial cues, especially in noise, instead of additional distraction. The visual analogy, while admittedly not perfect, is a way of explaining more simply the benefit of bilateral perceptual cues.

The other commonly cited clinical rationale for bilateral hearing aid use is related to the auditory deprivation effect (Silman et al., 1984). In individuals with bilateral hearing loss, there is concern that if only one hearing aid is used, the unaided ear will be deprived of sound and suffer additional deterioration. This appears to be a long term change in the unaided ear, affecting word recognition scores but not pure tone or speech reception thresholds.  Whether or not the unaided ear effect has implications for everyday hearing aid use and the ability to function in social and work-related situations requires further investigation to determine whether it is an important consideration for clinical recommendations.

Though most laboratory studies support the benefits of binaural listening, field studies and self-reports on bilateral hearing aid use have not always provided similar outcomes (Arlinger et al., 2003; Cox, 2011). For this reason, Noble reported on evidence from clinical trials to determine the conditions under which bilateral hearing aid use is most likely to be beneficial and to determine what patient attributes most support the recommendation of bilateral hearing aid use. Three of the reviewed studies were retrospective or reports from clinical patients occurring months or years after being fitted with unilateral or bilateral hearing aids. Two studies (Dirks & Carhart, 1962; Kochkin & Kuk, 1997) suggested that people who preferred bilateral hearing aid fittings had greater levels of hearing loss, though degree of hearing loss was not controlled. A third study by Noble, et al (1995) carefully matched 17 sets of unilateral and bilateral users according to degree of hearing loss. They examined speech reception and directional and distance spatial perception in aided and unaided conditions. Significant benefits were seen when comparing aided and unaided conditions but no differences were observed between unilaterally aided and bilaterally aided groups. The subject sample had mild to moderate hearing losses, so some caution should be taken when extrapolating these findings to individuals with more severe hearing losses.

In contrast, a study of new hearing aid users resulted in a two-to-one preference for unilateral use after a six-month period (Schreurs & Olsen, 1985). Individuals in this study wore one aid and two aids alternately for one week at a time, which arguably could have adversely influenced their acclimatization. Hearing aid users experience a sometimes extended period of adjustment to amplification (Keidser, 2009) which can affect their subjective judgments of sound quality and overall benefit (Bentler, et al, 1993). For instance, occlusion and unnatural perception of one’s own voice are qualities that can be annoying to new hearing aid users and are often more pronounced with bilateral hearing aids. Though these qualities almost always improve significantly with consistent bilateral use, it is not surprising that inexperienced, intermittent bilateral users might prefer the subjective sound quality of wearing one hearing aid at a time.  Additionally, Schreurs & Olsen’s study was conducted in 1985, at which time directional microphones were not in widespread use. Hearing aid users at that time often removed one hearing aid in noisy situations because bilateral omnidirectional microphones made surrounding noise sources too disruptive.  A field study of unilateral versus bilateral use with modern hearing aids, allowing for adequate acclimatization, might yield different results.

Two follow-up studies examined subjects that were slightly younger than a typical clinical population (Brooks & Bulmer, 1981; Erdman & Sedge, 1981). Both of these studies found that a majority of subjects preferred the use of two hearing aids.  These reports suggest that individuals whose activities require effective communication in challenging listening situations may prefer bilateral hearing aids. The remaining studies in Noble’s review were crossover studies, or experiments in which clinical patients were randomly assigned to a unilateral or bilateral condition and crossed over to the other condition after several weeks.  Stephens, et al (1991) found a greater degree of hearing loss and self-rated disability in the individuals who opted for bilateral hearing aid use; consistent with the retrospective reports of Dirks & Carhart (1962) and Kochkin & Kuk (1997) discussed earlier.

The studies examined in this literature review reveal several patterns. First, individuals with more severe hearing loss or perceived disability were more likely to prefer bilateral hearing aids. Subjects who preferred unilateral hearing aid use tended to have mild to moderate losses.  Second, participants employed in dynamic listening situations preferred bilateral hearing aid use, suggesting that individuals whose regular activities require effective communication in a variety of contexts may be more likely to benefit from the use of two hearing aids (Noble & Gatehouse, 2006).

Noble points out that laboratory studies cannot adequately consider the range of experiences encountered by hearing aid users in everyday situations. Laboratory research isolates variables for study, with subjects responding to specific stimuli in isolated, carefully contrasted conditions, whereas in everyday life, hearing aid users encounter a wide range of listening situations ranging from single speech sources in quiet conditions to multiple speech sources in the presence of competing noise. Conversely, clinical field trials probe the subjective responses of hearing aid users in a variety of real-world situations, but it can be difficult to extricate the specific variables affecting their perceptions. Though their outcomes may not always appear to be in agreement, both types of study provide useful information to guide clinical practice.

It is clear that bilateral hearing aid use has potential to reduce listening effort (Feuerstein, 1992), improve speech understanding, localization and receptiveness to lateral sounds (Noble & Gatehouse, 2006). Still, field studies consistently report a subset of patients that preference for unilateral hearing aid use. Whether environmentally or psychoacoustically motivated, the factors that underlie these preferences remain unclear. With consideration to documented benefits, bilateral hearing loss should first be treated with the prescription of bilateral hearing aids. Consideration for unilateral use should happen after the patient has adequate field experience and expresses subjective preference for the option of unilateral amplification.

References

Arlinger, S., Brorsson, B., Lagerbring, C., Leijon, A., Rosenhall, U. & Schersten, T. (2003). Hearing Aids for Adults – benefits and costs. Stockholm: Swedish Council on Technology Assessment in Health Care.

Bentler, R.A., Niebuhr, D.P., Getta, J.P. & Anderson, C.V. 1993b. Longitudinal study of hearing aid effectiveness. II. Subjective measures. Journal of Speech and Hearing Research 36, 820-831.

Byrne, D., Noble, W. & LePage, B. (1992). Effects of long0term bilateral and unilateral fitting of different hearing aid types on the ability to locate sounds. Journal of the American Academy of Audiology 3, 369-382.

Cox, R.M., Schwartz, K.S., Noe, C.M. & Alexander, G.C. (2011). Preference for one or two hearing aids among adult patients. Ear and Hearing 32 (2), 181-197.

Dillon, H. (2001). Monaural and binaural considerations in hearing aid fitting. In: Dillon, H., ed. Hearing Aids. Turramurra, Australia: Boomerang Press, 370-403.

Dirks, D. & Carhart, R. (1962). A survey of reactions from users of binaural and monaural hearing aids. Journal of Speech and Hearing Disorders 27(4), 311-322.

Feuerstein, J.F. (1992). Monaural versus binaural hearing: Ease of listening, word recognition and attentional effort. Ear & Hearing 13(2), 80-86.

Keidser, G., O’Brien, A., Carter, L., McLelland, M. & Yeend, I. (2009).  Variation in preferred gain with experience for hearing-aid users. International Journal of Audiology 2008 (47), 621-635.

Kochkin, S. & Kuk, F. (1997). The binaural advantage: Evidence from subjective benefit and customer satisfaction data. The Hearing Review, 4.

McArdle, R., Killion, M., Mennite, M. & Chisolm, T. (2012).  Are Two Ears Not Better Than One? Journal of the American Academy of Audiology 23, 171-181.

Noble, W. (2006). Bilateral hearing aids: A review of self-reports of benefit in comparison with unilateral fitting. International Journal of Audiology, 45(Supplement 1), S63-S71.

Noble, W. & Gatehouse, S. (2006). Effects of bilateral versus unilateral hearing aid fitting on abilities measured by the Speech, Spatial and Qualities of Hearing Scale (SSQ). International Journal of Audiology 45(2), 172-181.

Noble, W., TerHorst, K. & Byrne, D. (1995). Disabilities and handicaps associated with impaired auditory localization. Journal of the American Academy of Audiology 6(2), 129-140.

Silman, S., Gelfand, S. & Silverman, C. (1984). Late-onset auditory deprivation: Effects of monaural versus binaural hearing aids. Journal of the Acoustical Society of America 76, 1357-1362.