Distortion product otoacoustic emissions (DPOAE) were measured in normal-hearing and hearing-impaired human subjects. Analyses based on decision theory were used to evaluate DPOAE test performance. Specifically, relative operating characteristic (ROC) curves were constructed and the areas under these curves were used to estimate the extent to which normal and impaired ears could be correctly identified by these measures. DPOAE amplitude and DPOAE/noise measurements were able to distinguish between normal and impaired subjects at 4000, 8000, and, to a lesser extent, at 2000 Hz. The ability of these measures to distinguish between groups decreased, however, as frequency and audiometric criterion used to separate normal and hearing-impaired ears decreased. At 500 Hz, performance was no better than chance, regardless of the audiometric criterion for normal hearing. Cumulative distributions of misses (hearing-impaired ears incorrectly identified as normal hearing) and false alarms (normal-hearing ears identified as hearing impaired) were constructed and used to evaluate test performance for a range of hit rates (i.e., the percentage of correctly identified hearing-impaired ears). Depending on the desired hit rate, criterion values of -5 to -12 dB SPL for DPOAE amplitudes and 8 to 15 dB for DPOAE/noise accurately distinguished normal-hearing ears from those with thresholds greater than 20 dB HL for the two frequencies at which performance was best (4000 and 8000 Hz). It would appear that DPOAE measurements can be used to accurately identify the presence of high-frequency hearing loss, but are not accurate predictors of hearing status at lower frequencies, at least for the conditions of the present measurements.

The ability of transient-evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) to distinguish normal hearing from hearing impairment was evaluated in 180 subjects. TEOAEs were analyzed into octave or one-third octave bands for frequencies ranging from 500 to 4000 Hz. Decision theory was used to generate receiver operating characteristic (ROC) curves for each of three measurements (OAE amplitude, OAE/noise, reproducibility) for each OAE measure (octave TEOAEs, 1/3 octave TEOAEs, DPOAEs), for octave frequencies from 500 to 4000 Hz, and for seven audiometric criteria ranging from 10 to 40 dB HL. At 500 Hz, TEOAEs and DPOAEs were unable to separate normal from impaired ears. At 1000 Hz, both TEOAE measures were more accurate in identifying hearing status than DPOAEs. At 2000 Hz, all OAE measures performed equally well. At 4000 Hz, DPOAEs were better able to distinguish normal from impaired ears. Almost without exception, measurements of OAE/noise and reproducibility performed comparably and were superior to measurements of OAE amplitude, although the differences were small. TEOAEs analyzed into octave bands showed better performance than TEOAEs analyzed into 1/3 octaves. Under standard test conditions, OAE test performance appears to be limited by background noise, especially for the low frequencies.

Auditory brain stem responses (ABRs) were measured for stimuli presented both by air conduction and by bone conduction. Stimuli included clicks and tone bursts a t octave frequencies from 250 to 4000 Hz. ABR thresholds were comparable for airand boneconducted stimuli. Wave V latencies were longer for boneconducted stimuli compared to similar responses for air conduction. This effect was evident for both clicks and tone bursts. The fact that these latency differences were largely independent of stimulus spectrum suggests that they are not due t o differences between the frequency responses of air and bone conduction transducers. This finding is expected when one considers the interaction between output, threshold, and frequency for both transducer types. These data also s u p gest that there are inherent differences in transmission by air and bone conduction t h a t affect response latency but are unrelated to the amplitude spectrum in the signal.

Distortion product otoacoustic emission (DPOAE) data were obtained with a custom-designed system from 20 subjects with normal hearing. Cavity measurements, using this system and an Etymotic ER-10B low-noise microphone system, resulted in estimates of recording system distortion of -20 dB SPL for f2 frequencies ranging from 500 to 8000 Hz, and primary levels ranging from 20 to 75 dB SPL (L2 = L1-10 dB). Using this system it was possible to automatically adjust averaging time in order to obtain the same residual noise levels across frequencies. In all subjects with normal hearing, DPOAEs were measurable over a wide range of primary levels for octave f2 frequencies from 1000 to 8000 Hz, but not at 500 Hz. At 500 Hz, only half of the normal-hearing subjects produced DPOAEs that were above the noise floor. When they did, DPOAE amplitude was less than that observed at higher f2 frequencies. While the cause for response absence in some normal ears may have been due to residual noise, the reduced amplitude suggests that the other factors influence the measurement of DPOAEs at low frequencies. This result may be due to reduced cochlear production of DPOAEs at lower frequencies or reduced transmission through the middle ear.