Methods for the evaluation of hearing aids

Methods of hearing-aid evaluation are sub-divided into four broad categories, prescriptive selective amplification, selection from a set of existing hearing aids, use of a fixed frequency-gain characteristic, and adaptive fitting of a master hearing aid. The advantages, disadvantages, and controversies associated with each approach are reviewed and major research needs are discussed in the light of this review. Among the more important research needs are i) the development of improved speech tests that have low test-retest variability and which can discriminate between hearing aids with much greater precision than existing tests, ii) the development of reliable methods of predicting hearing-aid performance from audiological data, and iii) the determination of the optimum characteristics of the simplest, conventional hearing aid (i.e., a frequency-selective linear amplifier with no distortion other than peak clipping to limit maximum power output). It is also recommended that the simplest conventional hearing aid with gain, frequency-response, and clipping characteristics optimally matched to the subject's residual hearing be used as a reference for assessing more sophisticated hearing aids or alternative auditory prostheses for the hearing impaired. The third part of the paper provides a progress report on the development of a protocol for the prescriptive fitting of a wearable master hearing aid. The results to date show that the parameters of a conventional hearing aid can be adjusted according to well established optimization procedures so as to obtain superior, if not optimum, performance for each subject as a result of such individualized adjustments.