Distortion product otoacoustic emission test performance when both 2f(1)-f(2) and 2f(2)-f(1) are used to predict auditory status

The objective of this study was to determine whether distortion product oto acoustic emission (DPOAE) test performance, defined as its ability to disti nguish normal-hearing ears from those with hearing loss, can be improved by examining response and noise amplitudes at 2 f(1) - f(2) and 2 f(2) - f(1) simultaneously. In addition, there was interest in knowing whether measure ments at both DPs and for several primary frequency pairs can be used in a multivariate analysis to further optimize test performance. DPOAE and noise amplitudes were measured at 2 f(1) - f(2) and 2 f(2) - f(1) for 12 primary levels (L-2 from 10 to 65 dB SPL in 5-dB steps) and 9 pairs of primary fre quencies (0.5 to 8 kHz in 1/2-octave steps). All data were collected in a s ound-treated room from 70 subjects with normal hearing and 80 subjects with hearing loss. Subjects had normal middle-ear function at the time of the D POAE test, based on standard tympanometric measurements. Measurement-based stopping rules were used such that the test terminated when the noise floor around the 2 f(1) - f(2) DP was less than or equal to-30 dB SPL or after 3 2 s of artifact-free averaging, whichever occurred first. Data were analyze d using clinical decision theory in which relative operating characteristic s (ROC) curves were constructed and areas under the ROC curves were estimat ed. In addition, test performance was assessed by selecting the criterion v alue that resulted in a sensitivity of 90% and determining the specificity at that criterion value. Data were analyzed using traditional univariate co mparisons, in which predictions about auditory status were based only on da ta obtained when f(2) = audiometric frequency. In addition, multivariate an alysis techniques were used to determine whether test performance can be op timized by using many variables to predict auditory status. As expected, DP OAEs were larger for 2 f(1) - f(2) compared to 2 f(2) - f(1) in subjects wi th normal hearing. However, noise amplitudes were smaller for 2 f(2) - f(1) , but this effect was restricted to the lowest f(2) frequencies. A comparis on of signal-to-noise ratios (SNR) within nonnal-hearing cars showed that t he 2 f(1) - f(2) DP was more frequently characterized by larger SNRs compar ed to 2 f(2) - f(1). However, there were several subjects in whom 2 f(2) - f(1) produced a larger SNR. ROC curve areas and specificities for a fixed s ensitivity increased only slightly when data from both DPs were used to pre dict auditory status. Multivariate analyses, in which the inputs included b oth DPs for several primary frequency pairs surrounding each audiometric fr equency, produced the highest areas and specificities. Thus, DPOAE test per formance was improved slightly by examining data at two DP frequencies simu ltaneously. This improvement was achieved at no additional cost in terms of test time. When measurements at both DPs were;combined with data obtained for several primary frequency pairs and then analyzed in a multivariate con text, the best test performance was achieved. Excellent test performance (R OC) curve areas >0.95% and specificities >92% at all frequencies, including 500 Hz, were achieved for these conditions. Although the results described should be validated on an independent set of data, they suggest that the a ccuracy with which DPOAE measurements identify auditory status can be impro ved with multivariate analyses and measurements at multiple DPs. (C) 2000 A coustical Society of America. [S0001-4966(00)04204-1].