Distortion product otoacoustic emissions to single and simultaneous tone pairs.

Distortion product otoacoustic emissions (DPOAEs) evoked by single tone pairs and three simultaneous tone pairs were recorded in 60 normal-hearing adult ears. The purpose was to replicate a previous study using the commercially available probe assembly of the Grason Stadler GSI 60 and including ear of presentation in the statistical analysis along with frequency and condition. DPOAE levels were comparable between ears and conditions, although differences among frequencies were found. Noise levels were comparable between ears and tended to increase with increases in frequency for both conditions. The latter trend was not noted with the previous study and may be due to differences in the probe assembly and/or test environment. Further, noise levels were significantly greater at 2,000 and 8,000 Hz in the simultaneous condition. Caution should be exercised when interpreting results in the simultaneous condition because not all frequencies may have optimal signal-to-noise ratios when the test is terminated.