A wide range of signal modification for clinically prescribed hearing aids was ... analyses indicate that the amount of signal modification depends on acoustic factors ... The differences between the unaided and aided conditions decrease as the ... that 55 dB and 65 dB were not significantly different at 10 dB SNR (p>0.05).
Quantifying the Range of Signal Modification in Clinically-Fit Hearing Aids Varsha Rallapallia, Melinda Andersonb, James Katesc, Lynn Sirowd, Kathryn Arehartc, Pamela Souzaa,e Sciences & Disorders, Northwestern University; bUniversity of Colorado, School of Medicine; cUniversity of Colorado, Boulder; dI Love Hearing Inc., Port Washington; eKnowles Hearing Center, Northwestern University
Background & Significance
Acoustic Factors
Stimuli were two HINT (Nilsson et al., 1994) sentences, spoken by one male and one female talker, mixed in six-talker babble at different SNRs.
• 0 dB SNR • 5 dB SNR • 10 dB SNR • Quiet
Input Level • 55 dB SPL • 65 dB SPL • 75 dB SPL
Hearing Aid • HA-A (n=12) • HA-B (n=5) • HA-C (n=4)
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Signal Modification
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Acknowledgments: This work was supported by NIH R01 DC012289. Travel was funded by IHCON Student Scholarship. Thanks to Kailey Durkin & Sarah Mullervy for conducting the hearing aid recordings.
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Quiet
Fig. 5. Range of signal modification (CepCorr; yaxis) across the clinical hearing aid fittings (n=23), grouped by SNR and input level (x-axis).
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Fig. 6. Signal modification (CepCorr) as a function of four-frequency PTA (0.5, 1, 2, 4 kHz) in Quiet (left panel) and at 0 dB SNR (right panel). Dots represent the CepCorr for an individual hearing aid fitting. Colors represent different input levels.
Summary & Future Directions
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Increasing signal modification
Stimuli from PC → Data acquisition module (NI box) → Amplifier → Loudspeaker → KEMAR (Test=Aided; Ref=Unaided) → Preamplifier → Signal conditioner → NI Box → Output file recorded in PC
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Fig. 2. Schematic of the recording set up using KEMAR.
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Signal Modification Distribution
• Hearing aid fitting data presented here represent 14 males and 9 females in the age range of 51-91 yrs (M = 74.21 yrs).
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Fig. 4. Signal modification (CepCorr; y-axis) as a function of signal-to-noise ratio (SNR; x-axis) and input level (colored bars; see legend) collapsed across hearing aids. Error bars represent the standard error of mean. Pairwise comparisons at each SNR showed a significant difference in signal modification among all input levels (p 0.05). Signal modification for speech in babble recorded in the unaided condition (colored triangles) at a given SNR and input level, processed through the normal hearing system is shown for comparison.
Demographic & Audiological Info
Fig. 1. Individual audiograms (dashed colored lines; n=23) corresponding to the sample of clinical hearing aid fitting data. The average audiogram is represented by a solid black line.
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Hearing Aid Recording
Data collection
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Methods • Measurements were made from 6 commercially available receiver-in-the-canal hearing aids. Selection was based on the aids being the most commonly prescribed aids from 3 clinical sites. • The aids comprised 3 manufacturers * 2 technology levels. • The clinical sites included: • Northwestern University Center for Speech, Language, & Learning • University of Colorado Health Hearing & Balance Center, • A private audiology clinic in New York • De-identified clinical hearing aid fitting data for these devices were retrieved from the programming software and the final fitting parameter was used to program matching laboratory hearing aids. • The same coupling system prescribed to the patient was used. The coupling systems represented a range from fully open to fully closed domes. Custom molds were excluded. • Monaural hearing aid fittings were used (one ear per patient). No programming changes were made. • A subset of these data (n=23) from 3 out of 6 hearing aids each from a different manufacturer is presented here (data collection is ongoing).
• Statistical analysis was conducted using a repeated measures ANOVA model with SNR and input level as the within-subject factors and the hearing aid as the between-subjects factor. • Main effects and interaction between SNR and input level were significant (p < 0.001). • Pairwise comparisons at each SNR showed a significant effect of input level at each SNR. Tukey-Kramer adjustment was used to correct for multiple comparisons. • There were no significant differences in signal modification across the three hearing aids (p > 0.05).
0.8 CepCorr
Signal-to-noise ratio
55 dB SPL 65 dB SPL 75 dB SPL
CepCorr
1. To determine the distribution of signal modification in clinically-fit hearing aids. 2. To determine the effects of acoustic factors such as signal-to-noise ratio (SNR) and input level on these signal modifications.
Stimuli & Conditions
CepCorr
Objectives
Results
CepCorr
Hearing aids provide various signal processing techniques with a range of parameters to improve the listening experience for a hearing-impaired individual. We are motivated by the long-term goal of designing clinically usable metrics to individualize hearing aid fittings. In recent work, we reported significant differences in signal modification for mild versus strong signal processing in commercially available hearing aids (Kates et al., 2018). In this study, we extend this work to clinically prescribed hearing aid fittings based on standard-of-care guidelines (AAA Task Force, 2006).
Methods
Increasing signal modification
aCommunication
Fig. 3. Schematic of the signal modification metric. The reference was an unprocessed signal in quiet at 65 dB SPL, through a normal auditory system. The test signal (at a given SNR & input level) was processed with personalized hearing aid settings through an impaired auditory system. Signal modification of the test signal with respect to the reference signal was calculated using Cepstral Correlation (CepCorr).
For details on methodological considerations, please refer to Anderson et al. (this poster session).
• A wide range of signal modification for clinically prescribed hearing aids was measured in this study. Preliminary analyses indicate that the amount of signal modification depends on acoustic factors such as SNR and input level as well as audiological factors such as PTA. • In general, lower SNRs, higher input levels and more severity of hearing loss restricted the range of signal modification. • Findings are a proof-of-concept and are in accordance with previous research that used the same metrics with controlled hearing aid settings (Kates et al., 2018; Souza et al., 2018). • The differences between the unaided and aided conditions decrease as the level of noise in the signal increases, suggesting that the lower end of SNR is a limiting factor. • Work is underway to study the distribution of signal modification with more hearing aids, hearing aid signal processing settings, coupling systems, and common clinical diagnostic measures from a larger data set. • Future studies will be designed to characterize individual variability in the relationship between clinically-fit hearing aid signal modification and behavioral outcomes. References • • • •
American Academy of Audiology Task Force 2006. Guideline for audiologic management of the adult patient. Audiology Online. Kates, J. M., Arehart, K. H., Anderson, M. C., Kumar Muralimanohar, R., & Harvey, L. O., Jr. (2018). Using objective metrics to measure hearing aid performance. Ear and Hearing. Advance online publication. DOI: 10.1097/AUD.0000000000000574. Nilsson, M., Soli, S. D., Sullivan, J. (1994). Development of the hearing in noise test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America, 95, 1085–1099. Souza, P., K. Arehart, T. Schoof, M. Anderson, D. Stori, and L. Balmert. (2018). Understanding variability in individual response to hearing aid signal processing: results from a clinical trial. Submitted for publication.
