Difference in SII provided by initial fit and NAL-NL2 and its relation to self-reported hearing aid outcomes

Abstract

Objective

The speech intelligibility index (SII) is used to quantify the audibility of the speech. This study examined the relationship between self-reported hearing aid (HA) outcomes and the difference in aided SII (SII_A) calculated from the initial fit (IF) gain and that prescribed as per the second generation of National Acoustic Laboratory Non-Linear (NAL-NL2).

Design

A prospective observational study.

Study sample

The study included 718 first-time and 253 experienced HA users. All users had a valid real-ear measurement (REM) at three input levels (55, 65 and 80 dB SPL).

Results

The gain provided by IF was lower than NAL-NL2 at 55 and 65 dB SPL. IF gain exhibited reduced compression than NAL-NL2 as input levels increased from 55 to 80 dB SPL. On average, the SII_A provided by IF was significantly lower than that for NAL-NL2 at all input levels. The difference in SII_A between IF and NAL-NL2 at 80 dB SPL input level with 0 dB signal-to-noise ratio (SNR) turned out to be a predictor for self-reported outcome for first-time HA users.

Conclusion

The study suggests that an SIIA close to that provided by NAL-NL2 at high input levels would be preferred to obtain a better self-reported outcome. 

Keywords:

• Gain prescription
• hearing aids
• speech intelligibility index
• self-reported outcome

Acknowledgment

Collaboration and support by Innovation Fund Denmark (Grand Solutions 5164-00011B); Oticon^©, GN Hearing^©, Widex-Sivantos Audiology^© and other partners (Aalborg University Hospital, Odense University Hospital, Aalborg University, Technical University of Denmark, FORCE Technology and Copenhagen University Hospital) is sincerely acknowledged. The authors would like to acknowledge the efforts of Erik Schmidt, Vijay Narne and Gérard Loquet during the data collection and extraction of REMs. The authors would also like to thank Brent Edwards, Scott Brewer and NAL for providing the NAL-NL2 developer kit and Nikolai Bisgaard for coordinating with NAL.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by “Innovationsfonden”.