It has been proposed that the clinical accuracy of distortion product otoacoustic emissions (DPOAEs) is affected by the interaction of distortion and reflection sources contributing to the response. This study evaluated changes in dichotomous-decision test performance and threshold-prediction accuracy when DPOAE source contribution was controlled. Data were obtained from 205 normal and impaired ears with L 2 ranging from 0 to 80 dB SPL and f 2 = 2 and 4 kHz. Data were collected for control conditions (no suppressor, f 3 ) and with f 3 presented at 3 levels that previously had been shown to reduce the reflection-source contribution. The results indicated that controlling source contribution with a suppressor did not improve diagnostic accuracy (as reflected by ROC curve area) and frequently resulted in poorer test performance compared to control conditions. Likewise, correlations between DPOAE and behavioral thresholds were not strengthened when using the suppressors to control source contribution. While improvements in test accuracy were observed for a subset of subjects (normal ears with the smallest DPOAEs and impaired ears with the largest DPOAEs), the lack of improvement for the larger, unselected subject group suggests that DPOAEs should be recorded in the clinic without attempting to control the source contribution with a suppressor.

Objective-Calibration errors in distortion-product otoacoustic emission (DPOAE) measurements due to standing waves cause unpredictable changes in stimulus and DPOAE response level. The purpose of this study was to assess the extent to which these errors affect DPOAE test performance. Standard calibration procedures use sound pressure level (SPL) to determine specified levels. Forward pressure level (FPL) is an alternate calibration method that is less susceptible to standing waves. However, FPL derivation requires prior cavity measurements, which have associated variability. In an attempt to address this variability, four FPL methods were compared with SPL: a reference calibration derived from 25 measurements prior to all data collection and a daily calibration measurement, both of which were made at body and room temperature.Design-Data were collected from 52 normal-hearing and 103 hearing-impaired subjects. DPOAEs were measured for f 2 frequencies ranging from 2 to 8 kHz in half-octave steps, with L 2 ranging from −20 to 70 dB SPL (5-dB steps),. At each f 2 , DPOAEs were measured in five calibration conditions: SPL, daily FPL at body temperature (daily body), daily FPL at room temperature (daily room), reference FPL at body temperature (ref body), and reference FPL at room temperature (ref room). Data were used to construct receiver operating characteristic (ROC) curves for each f 2 , calibration method and L 2 . From these curves, areas under the ROC curve (A ROC ) were estimated.Results-The results of this study are summarized by the following observations: (1) DPOAE test performance was sensitive to stimulus level, regardless of calibration method, with the best test performance observed for moderate stimulus-level conditions. (2) An effect of frequency was observed for all calibration methods, with the best test performance at 6 kHz and the worst performance at 8 kHz. (3) At clinically applicable stimulus levels, little difference in test performance among calibration methods was noted across frequencies, except at 8 kHz. At 8 kHz, FPL-based calibration methods provided superior performance compared with the standard SPL calibration. (4) A difference between FPL calibration methods was observed at 8 kHz, with the best test performance occurring for daily body calibrations.Conclusions-With the exception of 8 kHz, there was little difference in test performance across calibration methods. At 8 kHz, A ROC s and specificities for fixed sensitivities indicate that FPL-based calibration methods provide superior performance compared with the standard SPL calibration for clinically relevant levels. Temperature may have an impact on FPL calculations relative to DPOAE test performance. Although the differences in A ROC among calibration procedures were not statistically significant, the present results indicate that standing-wave errors may impact DPOAE

Distortion-product otoacoustic emissions (DPOAEs) were used to describe suppression growth in normal-hearing humans. Data were collected at eight f 2 frequencies ranging from 0.5 to 8 kHz for L 2 levels ranging from 10 to 60 dB sensation level. For each f 2 and L 2 combination, suppression was measured for nine or eleven suppressor frequencies (f 3 ) whose levels varied from À20 to 85 dB sound pressure level (SPL). Suppression grew nearly linearly when f 3 % f 2 , grew more rapidly for f 3 < f 2 , and grew more slowly for f 3 > f 2 . These results are consistent with physiological and mechanical data from lower animals, as well as previous DPOAE data from humans, although no previous DPOAE study has described suppression growth for as wide a range of frequencies and levels. These trends were evident for all f 2 and L 2 combinations; however, some exceptions were noted. Specifically, suppression growth rate was less steep as a function of f 3 for f 2 frequencies 1 kHz. Thus, despite the qualitative similarities across frequency, there were quantitative differences related to f 2 , suggesting that there may be subtle differences in suppression for frequencies above 1 kHz compared to frequencies below 1 kHz.

Low-and high-frequency cochlear nonlinearity was studied by measuring DPOAE I/O functions at 0.5 and 4 kHz in 103 normal-hearing subjects. Behavioral thresholds at both f 2 's were used to set L 2 in dB SL for each subject. Primary levels were optimized by determining the L 1 resulting in the largest L dp for each L 2 for each subject and both f 2 's. DPOAE I/O functions were measured using L 2 inputs from −10 dB SL (0.5 kHz) or −20 dB SL (4 kHz) to 65 dB SL (both frequencies). Mean DPOAE I/O functions, averaged across subjects, differed between the two frequencies, even when threshold was taken into account. The slopes of the I/O functions were similar at 0.5 and 4 kHz for high-level inputs, with maximum compression ratios of about 4:1. At both frequencies, the maximum slope near DPOAE threshold was approximately 1, which occurred at lower levels at 4 kHz, compared to 0.5 kHz. These results suggest that there is a wider dynamic range and perhaps greater cochlearamplifier gain at 4 kHz, compared to 0.5 kHz. Caution is indicated, however, because of uncertainties in the interpretation of slope and because the confounding influence of differences in noise level could not be completely controlled.

Objective-Distortion-product otoacoustic emission (DPOAE) stimulus calibrations are typically performed in sound pressure level (SPL) prior to DPOAE measurements. These calibrations may yield unpredictable DPOAE response levels, presumably due to the presence of standing waves in the ear canal. Forward pressure level (FPL) has been proposed as an alternative method for stimulus calibration because it avoids complications due to standing waves. DPOAE thresholds following four FPL calibrations and one SPL calibration were compared to behavioral thresholds to determine which calibration results in data that yield the highest correlations between the two threshold estimates.Design-Fifty-two subjects with normal hearing and 103 subjects with hearing loss participated, with ages ranging from 11 to 75 years. These were the same individuals whose data were used to address the influence of calibration method on test performance in an accompanying paper (Burke et al., 2010). DPOAE input/output (I/O) functions were obtained at f 2 frequencies of 2, 3, 4, 6, and 8 kHz with the primary frequency ratio fixed at f 2 /f 1 ≈1.22. L 1 was set according to the equation L 1 =0.4L 2 +39 (Kummer et al. 1998(Kummer et al. , 2000 with L 2 levels ranging from −20 to 70 dB SPL and FPL in 5-dB steps. I/O functions were obtained at each frequency for each of five stimulus calibrations: SPL, daily FPL at room temperature, daily FPL at body temperature, reference FPL at room temperature, and reference FPL at body temperature. DPOAE thresholds were estimated using two methods. In the first, DPOAE threshold was taken as the lowest L 2 for which DPOAE level is 3 dB or greater above the noise floor (SNR ≥ 3 dB). In a second method, a linear regression method first described by Boege & Janssen (2002) and later adapted by Gorga et al. (2003), all DPOAE levels in each I/O function are converted to linear pressure and extrapolated to 0 μPa, where the L 2 is taken as threshold. Correlations of DPOAE thresholds with behavioral thresholds were obtained for each frequency, calibration method, and threshold-prediction method.Results-Correlations were greatest for frequencies of 3-6 kHz and lowest for 8 kHz, consistent with the previous frequency effects reported by Gorga et al. (2003). Calibration method made little difference in correlations between DPOAE and behavioral thresholds at any frequency. A small difference was noted in correlations for the two threshold-prediction methods, with the linear regression method yielding slightly higher correlations at all frequencies.Conclusions-Little difference in threshold correlations was observed among the five calibration methods used to calibrate the stimuli prior to DPOAE measurements. These results were not anticipated given the known effects of standing waves on ear-canal estimates of SPL at the plane of (Siegel, 1994;Siegel and Hirohata, 1994; Siegel, 2007; Driesbach and Siegel, 2001;Neely and Gorga, 1998;Scheperle et al., 2008). In addition, there was no effect of temperature (body vs. room) ...