Second Biennial Hearing Aid Research and Development Conference
September 22-24, 1997
National Institutes of Health
The Development of a New Fitting Procedure for Compression Amplification Based on Subjective Judgments
Jill E. Preminger,
Matthew Bakke, Arlene Neuman, The Lexington Center, Incorporated, Jackson Heights, New York
A new method for the individualized fitting of a two-channel, wide- dynamic-range compression hearing aid, based on the NAL-R prescriptive technique and individual subjective judgments of preference and/or clarity is under development. This is a report on the first phase of the project.
Twelve experienced hearing aid users with mild to moderate sensorineural hearing losses served as subjects. Each subject was fit with a compression hearing aid set for linear amplification and output compression limiting using the NAL-R prescriptive method. In laboratory sessions, paired-comparison judgments for clarity and for preference were obtained for three different speech levels, 50 dB Leq (quiet speech), 60 dB Leq (average speech), and 80 dB Leq (loud speech). The speech was presented in two different competing noises, ventilation noise, and cafeteria noise. The frequency-gain characteristics to be considered consisted of the NAL-R target and 24 variations of systematic decreases and boosts to the gain in the low and high frequency bands of the hearing aid using the Simplex procedure. The selected frequency-gain characteristics were validated with the CUNY Nonsense Syllable Test. Based on the subjective and objective test results, target compression thresholds and compression ratios were calculated.
The results demonstrated that the majority of listeners did not select the NAL-R frequency response for either clarity or preference, for the quiet speech, average speech or loud speech inputs. In addition, there was no consistency in desired frequency gain characteristics across hearing-impaired listeners. This indicates that preference and/or clarity measures must be made for individuals and can not be predicted based on group data. Finally, the target compression thresholds and compression ratios determined from the present experiment were different from those calculated by the IHAFF procedure, and there was no consistent relationship between the results from the two procedures across the listeners with hearing loss.
[Supported by the NIDRR, U.S. Department of Education]
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