![]() Almost since the development of the wearable electronic hearing aid (one that encompassed high gain, good reliability, and design flexibility), the issue of monaural versus bilateral fittings has been debated. Whether bilateral is superior to monaural amplification is a long-standing question. THE EBB AND FLOW OF BILATERAL HEARING AIDS: A BRIEF HISTORY This article is concerned with localization ability and the pros and cons of bilateral amplification. Directional microphone hearing aids can also improve speech intelligibility under these conditions, and enthusiasm is growing for this form of amplification as discussed in the article by Todd Ricketts. Two key advantages of bilateral amplification are directional hearing and improved intelligibility of speech and noise from different directions. However, the enthusiasm for bilateral amplification has resurfaced and in the past decade more bilateral than monaural hearing aids have been dispensed. Following the initial enthusiasm, a down period occurred in the 1960s because of the lack of objective studies on improvements in speech intelligibility with bilateral hearing aids and the reluctance of consumers to wear two of the bulky instruments. This excitement was fueled by the studies of Hirsh and Licklider and the theoretical and clinical arguments of Bergman, Carhart, and DiCarlo and Brown. Initially, a great deal of excitement existed over the prospect of improvement in speech intelligibility and localization with the use of bilateral hearing aids. Since a true binaural hearing aid is not yet available, we will refer to all hearing aids fit for two ears as bilateral. The importance of true binaural and the insufficiency of simple bilateral hearing aids have been emphasized. Some interaction between both hearing aids is necessary to access the binaural advantage. The common assumption that two optimally fit monaural hearing aids constitute an optimum binaural fit is not necessarily true. This has important implications for those patients who receive monaural amplification during the ebb phase. ![]() The evolution of bilateral amplification has occurred at a slow pace. ![]() In some cases, evolution can be very rapid, as in the case of the cochlear implant in other cases, the evolutionary development is slow and spans many decades. The pattern is essentially one of evolution rather than revolution. A gradual settling down follows in which both the potential and limitations of these developments are recognized this results in a new generation of sensory aids that embody significant, albeit undramatic, improvements. With time, enthusiasm wanes as expectations are not met and new studies illuminate newer insights and more realistic outcomes. Glowing papers are published and skeptics are held at bay. Each new advance is met with considerable fanfare and much anticipation. There is an ebb and flow in the development of sensory aids. These data show that asymmetry in localization judgments is a much more sensitive indicator of abnormal localization ability than the magnitude of localization errors. In this article, we will address the advantages of bilateral hearing aids and reveal some new localization data that show that most listeners with bilateral amplification, when tested unaided, as well as normal-hearing listeners manifested very high degrees of symmetry in their judgments of perceived angle while listeners who routinely use monaural amplification and those with asymmetric hearing loss had relatively large asymmetries. However, it is now assumed that bilateral amplification has significant advantages over monaural amplification in most cases, a view that is supported by our localization results. Determining whether a bilateral hearing aid fitting is superior to that of a monaural hearing aid is a long-standing question for this reason, the trend toward bilateral amplification has been slow. Abstract - This article is concerned with the evolution and pros and cons of bilateral amplification.
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