Distortion product otoacoustic emission test of sensorineural hearing loss in humans: comparison of unequal- and equal-level stimuli.

Distortion product otoacoustic emissions (DPOEs) at the frequency of 2f1 -f2 (f1 < f2) were measured in 77 human adult ears with normal hearing or sensorineural hearing loss. The purpose of this study was to compare the performances of DPOE tests conducted with two sets of stimuli: 1) L1 = 65, L2 = 50 dB sound pressure level (SPL) re 20 microPa ("65/50"), and 2) L1 = L2 = 65 dB SPL ("65/65"). Half-octave DPOE root-mean-square levels at 1,000, 2,000, 4,000, and 6,000 Hz were computed from the initial DPOEs measured at 0.25-octave intervals. Correlation coefficient and decision-theory analyses were applied to evaluate the DPOE test performance. For both stimuli, DPOE level exhibited significant correlation with pure tone hearing threshold. When the criterion DPOE level distinguishing normal from impaired hearing was adjusted, the curves of sensitivity and specificity crossed, and the values at the crossing were higher than 80% at frequencies of 2,000 to 6,000 Hz for both stimuli. The area under the receiver operating characteristic (ROC) curve, which provides an overall evaluation of the test performance independent of the criterion DPOE level, was .90 or higher at 2,000 to 6,000 Hz for both stimuli. At 2,000 and 4,000 Hz, all measures of test performance were higher for the 65/50 stimulus than the 65/65 stimulus: area under the ROC curve (.96 to .97 versus .90 to .91, statistically significant, p < .001, Wilcoxon test), sensitivity/specificity (90% to 93% versus 80% to 85%), and correlation coefficient (.78 to .87 versus .66 to .79). At 1,000 and 6,000 Hz, the performances of the DPOE tests were similar for the two stimuli. These results support the conclusion that a DPOE test with L1 = 65 and L2 = 50 dB SPL provides a better performance than that with L1 = L2 = 65 dB SPL and recommend the use of stimuli with L1 being higher than L2 by about 15 dB. These results also support a growing view that 2f1-f2 DPOEs can be utilized clinically as a reliable method of testing human sensorineural hearing loss.