An adaptive response hearing aid for high frequency hearing loss
A new approach to the evaluation of hearing aid fitting has suggested that an adaptive frequency/gain characteristic is subjectively more beneficial for patients with precipitous high frequency hearing loss, listening to speech in the various quiet and noisy situations encountered in everyday life. The development and evaluation of such a hearing aid is described. Parameters for the operation of the adaptive response mechanism were determined experimentally by means of subjective listening tests using subjects with precipitous high frequency hearing loss. Software was compiled to implement these parameters on a specially designed, computer-controlled, master hearing aid system in real time. A novel evaluation procedure was developed in order to assess the benefits provided by this system in terms of objective speech discrimination measures and subjective judgements in simulations of real life listening conditions. Uncertainty about the effects of binaural hearing aid fitting and, in particular, the lack of scientific evidence of any subjective advantages to be gained, led to a secondary study of the benefits of fitting a preferred monaural response binaurally. The hypothesis that the adaptive frequency response hearing aid is more appropriate than a standard fixed frequency response aid for people with precipitous high frequency hearing loss, listening to speech in the variety of quiet and noisy situations encountered in everyday life, was partially upheld in that it was preferred by a significant number of patients with 4kHz hearing loss greater than, or equal to, 65 dBHL. However, for patients with less severe high frequency hearing loss, a flat frequency response was preferred. A secondary hypothesis, that binaural fitting of a person's preferred monaural hearing aid response provides further increases in benefit over those found for the monaural fitting, was upheld. Further findings with important implications for hearing aid fitting, both monaural and binaural, are discussed together with important directions for future work.