False air-bone gaps at 4 kHz in listeners with normal hearing and sensorineural hearing loss

Abstract

Objective: This report presents data from four studies to examine standard bone-conduction reference equivalent threshold force levels (RETFL), especially at 4 kHz where anomalous air-bone gaps are common. Design: Data were mined from studies that obtained air- and bone-conduction thresholds from normal-hearing and sensorineural hearing loss (SNHL) participants, using commercial audiometers and standard audiometric transducers. Study sample: There were 249 normal-hearing and 188 SNHL participants. Results: (1) Normal-hearing participants had small air-bone gaps at 0.5, 1.0, and 2.0 kHz (‐1.7 to 0.3 dB) and larger air-bone gaps at 4 kHz (10.6 dB). (2) SNHL participants had small air-bone gaps at 0.5, 1.0, and 2.0 kHz (‐0.7 to 1.7 dB) and a larger air-bone gap at 4 kHz (14.1 dB). (3) The 4-kHz air-bone gap grew with air-conduction threshold from 10.1 dB when the air-conduction threshold was 5–10 dB HL to 21.1 dB when the air-conduction threshold was greater than 60 dB. (4) With the 4-kHz RETFL corrected by the average SNHL air-bone gap, the relationship between RETFL and frequency is linear with a slope of − 12 dB per octave. Conclusions: The 4-kHz air-bone gaps for listeners with SNHL could be avoided by adjusting the 4-kHz RETFL by − 14.1 dB.

Key Words::

• Audiometry
• automated audiometry
• hearing
• hearing test
• air conduction
• bone conduction
• threshold
• air-bone gap
• artificial mastoid

Notes

1. Bone-conduction RETFLs are identical in the two standards.

Acknowledgements

We are grateful to Chris Bauch, Don Dirks, Douglas Keefe, Wayne Olsen, Sunil Puria, Bill Rabinowitz, John Rosowski, and Jozef Zwislocki for helpful discussions concerning the interpretation of the data. We thank Brian Glasberg at the University of Cambridge for his assistance with statistical analysis, and Michael Hunter and his team on the Busselton Healthy Ageing Study for managing the data collection and collation of Study 4. Guy Lightfoot and one anonymous reviewer provided helpful comments that improved the article.

Declaration of interest: The first author is president of Audiology Incorporated (AI) which owns intellectual property that was used in some of the studies reported in this article. That intellectual property may be incorporated into commercial products. AI has developed and plans to commercialize a bone-conduction calibration coupler (described in Margolis and Stiepan, 2012). The other authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Portions of this work were supported by grants R41DC05110 and RC3DC010986 from the National Institutes of Deafness and Other Communication Disorders.