Second Biennial Hearing Aid Research and Development Conference

September 22-24, 1997
National Institutes of Health
Bethesda, Maryland

Restoring Normal Loudness Perception as a Function of Fitting Protocol and Technology

The goal of traditional hearing aid fittings has been to make sound audible but not uncomfortable. Recently, investigators have suggested that technology is available in the form of compression signal processing that will allow individuals to perceive loudness normally as a function of frequency and input intensity level. The potential and reality of restoring normal loudness perception to individuals with hearing loss is impacted by the technology available and fitting strategies applied to that technology. Although the concept of loudness restoration has become popular with the developers of both hearing aids and fitting protocols, little frequency specific verification data have been collected in order to determine if normal loudness perception has been restored.

Fifty adult subjects with hearing loss between 15 and 40 dB at 500 Hz and 40 and 80 dB at 4000 Hz were fit with the Siemens MUSIC completely-in-the-canal hearing aids. This is a wide dynamic range, two-channel, curvilinear compression instrument. The initial fitting was based on the DSL[i/o] fitting strategy using loudness judgments obtained from the Contour Test at 500, 1000, 2000, 3000, and 4000 Hz. The original parameters of the fit (overall gain, slope, etc.) were optimized by performing the Contour Test for warble tones and speech in the soundfield. The hearing aids were manipulated until normal loudness growth was optimized across frequencies as evidenced by loudness contours that matched loudness contours previously obtained on normal hearing individuals.

The individual and group data that will be presented will include the amount of change to the original DSL[i/o] fitting by parameter (overall gain, slope, etc.) that is required to achieve a return to normal loudness growth. In addition, real-ear-to-coupler-differences (RECD) obtained for each ear of each individual will be compared with the needed changes to optimize fit in order to quantify whether fine-tuning could be minimized by employing RECD in the original fitting with adult ears.

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