Influences of stimulus and response calibrations on level maps of pulsed distortion-product otoacoustic emissions

Distortion-product otoacoustic emissions (DPOAEs) are widely used to assess cochlear function, but their diagnostic value is limited by interference between DPOAE components, dependence on optimal stimulus levels, middle-ear transmission, and variability due to ear-canal acoustics. Pulsed DPOAE level maps (LMs), which allow the derivation of estimated distortion-product thresholds (L2,EDPT), address some of these limitations. However, their reliability may still be compromised by standing-wave phenomena and calibration errors. In this study, we systematically compared four calibration methods-standard sound-pressure level (SPL), forward pressure level (FPL), integrated pressure level (IPL), and the combined methods of IPL and emitted pressure level (EPL), denoted as IPL+EPL-on LMs in eleven subjects across two sessions with intentionally varied probe insertion depths. Both FPL and IPL significantly reduced the intersession variability of LM-parameters compared with SPL, while IPL performed consistently better. The IPL+EPL calibration demonstrated additional benefits in reducing standing-wave effects on DPOAE and derived quantities. The analysis of three parameters describing the dependence of DPOAE on the two primary levels L2 and L1, confirmed that calibration-dependent changes in LM parameters could be interpreted as conduction loss (or gain) specifically for the frequencies f1, f2, and fDP. Advanced calibration methods, particularly IPL, substantially improve the reliability of LMs and enhance their potential for clinical audiometric applications.