Evaluation of the desired sensation level [Input/Output] algorithm for adults with hearing loss: The acceptable range for amplified conversational speech

Objectives: This study had two related purposes: first, to define the range of optimal ear canal levels of aided speech in both high frequency and low frequency regions for adults, using both subjective and objective definitions of optimal; and second, to determine whether a prescribed frequency response, such as that given by Desired Sensation Level [Input/Output], falls within the adult listener's optimal range. Design: Twenty-three adult listeners with mild to moderately severe sensorineural hearing loss were selected from a pool of research volunteers. They were fitted in the laboratory with the Siemens Signia hearing instrument and tested with 20 nominally different frequency responses. All advanced processing options of the hearing instrument were disabled. Subjective ratings,of loudness and quality and objective measures of consonant identification were obtained for every frequency response. Results: These adult listeners had, on average, a 10 dB range of measured responses in both the low and the high frequencies that resulted in optimal performance on all the measurements. The range did not vary with degree or configuration of hearing loss, or previous hearing aid experience. Desired-Sensation-Level Input/Output targets were within the optimal range for the low frequencies, and 3 dB above the optimal range for the high frequencies. Conclusions: A range of aided ear canal frequency responses was determined within which adults with mild to moderately severe hearing loss performed optimally on both objective and subjective outcomes. Clinical implications of this finding include the following: prescriptive methods providing different targets may all result in optimal fittings; and a range of targets may be more appropriate than a single target when setting the frequency-gain characteristics of the hearing instrument.