Comparison of hearing aids over the 20th century

Objective: To measure hearing aid performance using circuitry representativ e of the major eras of technological advancement during the 20th century. Design: Twenty subjects with audiometric profiles consistent with hearing a id candidacy were fit with each of seven hearing aids. No directional micro phones were used and binaural benefit was not assessed. Each hearing aid wa s fit to the strategy or fitting scheme of the era, or that which was inten ded by the presenting manufacturer. Electroacoustic and/or real ear measure s of gain, output, bandwidth, and distortion were obtained. Objective outco me measures assessing speech perception in backgrounds of noise were obtain ed. Subjective outcome measures of sound quality and ease of listening were obtained in the laboratory and in real life settings. Results: Electroacoustic and real ear measures indicate that gain and bandw idth have increased, and output and distortion have decreased with current electronic aids. Speech perception ability across the different outcome mea sures showed significantly poorer performance with the body and linear hear ing aids when input levels were high; when input levels were low, outcome m easures with hearing aids using a dynamic range compression were not negati vely affected. At the most adverse signal to noise ratios, none of the hear ing aids was shown to be superior. Measured bandwidth did not correlate hig hly with speech perception ability for any of the objective outcome measure s used. For the subjective measures of sound quality done in a blinded mann er, no significant differences were found across different listening situat ions for current hearing aids. Conclusions: The two most important factors for aided speech perception app ear to be the audibility and distortion of the signal. No current compressi on scheme proved superior with the outcome measures used in this investigat ion.