CLINICAL-SIGNIFICANCE OF RELATIVE PROBE-TONE LEVELS ON DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS

The effect of systematic variations in the relative levels (L1, L2) of two primary tones (f1, f2) on the amplitude of the distortion product otoacoustic emission (DPOAE) at 2f 1-f2 and f1 < f2 was investigated in 14 ears from 7 normally hearing human subjects. The primary tones ( f2:f1 = 1.23) were geometrically centred at the standard clinical freq uencies of 0.5, 1, 1.5, 2, 3, 4,6 and 8 kHz. The quantity L1-L2 was va ried systematically from -10 dB through + 10 dB with L2 held constant at 75 dB SPL for negative values, L1 held constant at 75 dB SPL for po sitive values, and L1 = L2 = 75 dB SPL at 0 dB relative difference. Th e maximum amplitudes of the distortion products were generated when L1 = L2 at all geometric centre frequencies except 8 kHz. The reduction of the DPOAE with reduction of Ll was linear at a rate that gradually increased as a function of geometric mean frequency. To a lesser exten t, the reduction of the DPOAE with reduction of L2 also was linear but at a rate that systematically decreased as a function of geometric me an frequency. The results suggest, that to maximize the level of the d istortion product for clinical purposes, the relative levels of the pr imary tones should be equal to each other, at least when overall stimu lus levels are around 75 dB SPL and f2:f1 = 1.23.