Bimodal hearing refers to the combination of the cochlear implant in one ear and the hearing aid in the opposite ear. Recently, cochlear implant candidacy criteria have been expanded and the number of people receiving cochlear implants with residual hearing has increased, leading to the raised bimodal population. Providing professional fitting services based on systematic bimodal fitting methods or guidelines are essential for the successful bimodal intervention of the hearing impaired. However, there is a lack of evidence-based bimodal fitting method or guideline clinically applicable. In general, bimodal fitting consists of three areas of fitting; cochlear implant mapping, hearing aid fitting, and bimodal fitting. Among them, establishing evidence-based bimodal hearing aid fitting will be a key factor to improve bimodal fitting services of hearing aid centers. The purpose of this study is to review recent literature related to bimodal hearing aid fitting to establish bimodal hearing aid fitting guidelines for hearing aid professionals. This review involves five bimodal hearing aid fitting issues including frequency response, loudness, dynamic compression, frequency transposition, and hearing aid fitting formula. In addition, it described three recent clinical bimodal hearing aid fitting guidelines provided by manufacturers. Two factors contributing to bimodal hearing aid fitting optimization across the studies are frequency response and loudness balance. Conducting loudness balance in bimodal hearing devices and adjusting gains based on the loudness balance tests are one of the important procedures for bimodal fitting optimization. Hearing aid fitting based on wide-band frequency responses and conventional hearing aid formula is recommended for the initial step of the bimodal fitting.
MATERIALS AND METHODS