Benefits of Nonlinear Frequency Compression in Adult Hearing Aid Users
Authors: Kokx-Ryan Melissa , Cohen Julie , Cord Mary T. , Walden Therese C. , Makashay Matthew J. , Sheffield Benjamin M. , Brungart Douglas S. 
Published: July 2015

Background:Frequency-lowering (FL) algorithms are an alternative method of providing access to high-frequency speech cues. There is currently a lack of independent research addressing: (1) what functional, measureable benefits FL provides; (2) which, if any, FL algorithm provides
the maximum benefit, (3) how to clinically program algorithms, and (4) how to verify algorithm settings.Purpose:Two experiments were included in this study. The purpose of Experiment 1 was to (1) determine if a commercially available nonlinear frequency compression (NLFC) algorithm
provides benefit as measured by improved speech recognition in noise when fit and verified using standard clinical procedures; and (2) evaluate the impact of acclimatization. The purpose of Experiment 2 was to (1) evaluate the benefit of using enhanced verification procedures to systematically
determine the optimal application of a prototype NLFC algorithm, and (2) determine if the optimized prototype NLFC settings provide benefit as measured by improved speech recognition in quiet and in noise.Research Design:A single-blind, within-participant repeated measures design in
which participants served as their own controls.Study Sample:Experiment 1 included 26 participants with a mean age of 68.3 yr and Experiment 2 included 37 participants with a mean age of 68.8 yr. Participants were recruited from the Audiology and Speech Pathology Center at Walter Reed
National Military Medical Center in Bethesda, MD.Intervention:Participants in Experiment 1 wore bilateral commercially available hearing aids fit using standard clinical procedures and clinician expertise. Participants in Experiment 2 wore a single prototype hearing aid for which FL
settings were systematically examined to determine the optimum application. In each experiment, FL-On versus FL-Off settings were examined in a variety of listening situations to determine benefit and possible implications.Data Collection and Analysis:In Experiment 1, speech recognition
measures using the QuickSIN and Modified Rhyme Test stimuli were obtained at initial bilateral fitting and 3‐5 weeks later during a follow-up visit. In Experiment 2, Modified Rhyme Test, /s/, /∫/ consonant discrimination task, and dual-task cognitive load speech recognition performance
measures were conducted. Participants in Experiment 2 received four different systematic hearing aid programs during an initial visit and speech recognition data were collected over 2‐3 follow-up sessions.Results:Some adults with hearing loss obtained small-to-moderate benefits
from implementation of FL, while others maintained performance without detriment in both experiments. There was no significant difference among FL-On settings systematically obtained in Experiment 2. There was a modest but significant age effect in listeners of both experiments that indicated
older listeners (>65 yr) might benefit more on average from FL than younger listeners. In addition, there were reliable improvements in the intelligibility of the phonemes /ŋ/ and /b/ for both groups, and /ð/ for older listeners from the FL in both experiments.Conclusions:Although
the optimum settings, application, and benefits of FL remain unclear at this time, there does not seem to be degradation in listener performance when FL is activated. The benefits of FL should be explored in older adult (>65 yr) listeners, as they tended to benefit more from FL applications.