29.06.2012
The reference hearing thresholds for a commercially available otoacoustic emission probe were determined. This will enable the application of this probe also in subjective hearing tests.
Distortion product otoacoustic emissions (DPOAE) are signals measured in the ear canal as a response of the healthy inner ear to two well-defined tones. To relate the DPOAE results to the behavioral hearing threshold of a patient, it proves advantageous to employ the very same probe in both measurements. However, no reference hearing thresholds for DPOAE probes exist so far.
What is a reference hearing threshold?
A reference hearing threshold reflects the average hearing threshold of an adult population with healthy hearing. This is determined on the basis of a representative group of young normal-hearing test subjects. Consistent reference hearing thresholds are a prerequisite for comparable hearing threshold measurements by different ENT specialists.
Our study
In our study [1], we determined the reference hearing thresholds for the commonly available Etymotic Research ER-10C DPOAE probe (Fig. 1). The test subjects were instructed to respond to pure tones, presented by the probe, by pressing a button. This way, the individual hearing thresholds of the test subjects were determined using an automated algorithm at each test frequency. Finally, the average stimulus amplitudes at the hearing thresholds were reproduced in an occluded-ear simulator, yielding the frequency-dependent reference hearing thresholds for the DPOAE probe.
Figure 1: Procedure for determining the reference hearing thresholds for the DPOAE probe. The test signals were delivered by one of the probe loudspeakers. The stimulus amplitudes at the hearing threshold of a group of normal-hearing test subjects were recorded in the form of input voltage levels. In a second step, the respective sound pressure levels were reproduced in an occluded-ear simulator, yielding the required reference hearing thresholds for this probe. The hearing tests were performed in the calm anechoic room of PTB.
The knowledge of the reference zero for this probe opens up the possibility of (objective) DPOAE measurements and (subjective) pure-tone audiometry using one and the same probe. The presented data provide a first step towards standardization of reference hearing thresholds for this probe.
Literature:
[1] Zebian M, Hensel J, Fedtke T, Vollbort S (2012). “Equivalent hearing threshold levels for the Etymotic Research ER-10C otoacoustic emission probe”. International Journal of Audiology, doi:10.3109/14992027.2012.669050 : 
http://informahealthcare.com/doi/abs/10.3109/14992027.2012.669050
Contact person:
Makram Zebian, Dept. 1.6, WG 1.61, E-mail: 
makram.zebian(at)ptb.de