Do “Optimal” Conditions Improve Distortion Product Otoacoustic Emission Test Performance?

Abstract

Objectives To determine whether an “optimal” DPOAE protocol including (1) optimal stimulus levels and primary-frequency ratios for each f2, (2) simultaneously measuring 2f2-f1 and 2f1-f2 distortion products, (3) controlling source contribution, (4) implementing improved calibration techniques, (5) accounting for the influence of middle-ear reflectance, and (6) applying multivariate analyses to DPOAE data results in improved accuracy in differentiating between normal-hearing and hearing-impaired ears, compared to a standard clinical protocol. Design Data were collected for f2 frequencies ranging from 0.75 to 8 kHz in 28 normal-hearing and 78 hearing-impaired subjects. The protocol included a control condition incorporating standard stimulus levels and primary-frequency ratios calibrated with a standard sound pressure level (SPL) method and three experimental conditions using optimized stimuli calibrated with an alternative forward pressure level (FPL) method. The experimental conditions differed with respect to the level of the reflection-source suppressor tone, and included conditions referred to as the null-suppressor (i.e., no suppressor tone presented), low-level suppressor (i.e., suppressor tone presented at 58 dB SPL), and high-level suppressor (i.e., suppressor tone presented at 68 dB SPL) conditions. The area under receiver operating characteristic (AROC) curves and sensitivities for fixed specificities (and vice versa) were estimated to evaluate test performance in each condition. Results AROC analyses indicated (1) improved test performance in all conditions using multivariate analyses, (2) improved performance in the null-suppressor and low-suppressor experimental conditions compared to the control condition, and (3) poorer performance below 4 kHz with the high-level suppressor. As expected from AROC, sensitivities for fixed specificities and specificities for fixed sensitivities were highest for the null-suppressor and low-suppressor conditions and lowest for standard clinical procedures. The influence of 2f2-f1 and reflectance on test performance was negligible. Conclusions Predictions of auditory status based on DPOAE measurements in clinical protocols may be improved by the inclusion of (1) optimized stimuli, (2) alternative calibration techniques, (3) low-level suppressors, and (4) multivariate analyses.

Distribution of standing-wave errors in real-ear sound-level measurements

“…The extent of transmission of sounds through the TM at certain frequencies could therefore be more predictive of test performance than standing-wave effects. However, this hypothesis was not supported by Kirby et al (2011), who found no correlation between reflectance and DPOAE test performance.…”

“…Although calibration errors were evident at other frequencies, the distribution of error magnitudes does not provide an explanation for the poorer test performance at 8 kHz in the Burke et al study. However, the results of Scheperle et al (2008) and Kirby et al (2011) suggest value in continuing to explore FPL as an alternative method of calibration for DPOAEs.…”

“…In a recent study by Kirby et al (2011), an effect of calibration method was observed, but only when previously determined optimal stimulus conditions (including primarylevel and primary-frequency ratios) were used (Neely et al, 2005;Johnson et al, 2006). This effect was accentuated when the alternative calibration method (daily FPL calibrations at body temperature) and optimal stimulus conditions were combined with multivariate analyses of DPOAE data.…”

Further assessment of forward pressure level for in situ calibration

“…Similarly, Rogers et al (2010) failed to demonstrate that FPL calibration improved threshold predictions. In contrast, Kirby et al (2011) found a significant improvement in test performance when FPL calibration was used; however, the calibration method was paired with optimized stimulus levels, and the sources of improvement could not be examined independently.…”

“…Several investigators have tested whether the theoretical advantages of quantifying ear-canal sound level in FPL are apparent empirically using distortion product otoacoustic emissions (DPOAE) or behavioral thresholds as outcome measures (DPOAEs: Scheperle et al, 2008;Burke et al, 2010;Rogers et al, 2010;Kirby et al, 2011. Behavioral Thresholds: Withnell et al, 2009McCreery et al, 2009;Lewis et al, 2009).…”