DISTORTION-PRODUCT OTOACOUSTIC EMISSION TEST OF SENSORINEURAL HEARING-LOSS IN HUMANS - COMPARISON OF UNEQUAL-LEVEL AND EQUAL-LEVEL STIMULI

Distortion product otoacoustic emissions (DPOEs) at the frequency of 2 f1 - f2 (f1 < f2) were measured in 77 human adult ears with normal hea ring or sensorineural hearing loss. The purpose of this study was to c ompare the performances of DPOE tests conducted with two sets of stimu li: 1) L1 = 65, L2 = 50 dB sound pressure level (SPL) re 20 mu Pa (''6 5/50''), 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 signifi cant correlation with pure tone hearing threshold. When the criterion DPOE level distinguishing normal from impaired hearing was adjusted, t he curves of sensitivity and specificity crossed, and the values at th e crossing were higher than 80% at frequencies of 2,000 to 6,000 Hz fo r both stimuli. The area under the receiver operating characteristic ( ROC) curve, which provides an overall evaluation of the test performan ce 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 sti mulus: area under the ROC curve (.96 to .97 versus .90 to .91, statist ically significant, p < .001, Wilcoxon test), sensitivity/specificity (90% to 93% versus 80% to 85%), and correlation coefficient (.78 to .8 7 versus .66 to .79). At 1,000 and 6,000 Hz, the performances of the D POE 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 = 1,2 = 65 dB SPL and recommend the use of stimuli with L1 being higher than 1,2 by about 15 dB. These results also support a growing view that 2f1 - f2 DPOEs can be utiliz ed clinically as a reliable method of testing human sensorineural hear ing loss.