Effects of relative levels of the primary tones on distortion product otoacoustic emissions in normal-hearing subjects.

This study investigated the effects of the relative levels of the two primary tones, L1 and L2, on the amplitude of distortion product otoacoustic emissions (2F1-F2). Testing was conducted with a commercially available system for measuring DPOAEs (Grason-Stadler, GSI-60). The intensity of the lowest primary tone (L1) remained constant at 75, 65, 55 or 45 dB SPL while L2 varied over a 20 dB range around L1, i.e. L1-L2 was -5, 0, 5, 10 or 15 dB. For example, when L1 was 75 dB SPL, L2 was presented at 80, 75, 70, 65 or 60 dB SPL. Thirty normal-hearing women were presented with 11 pairs of primary tones having geometric means ranging from 531 Hz to 5531 Hz. A constant F2:F1 ratio of 1.21 was used. The results revealed that when L1 was 75 dB SPL, the largest distortion products were observed across all frequencies for the 0 dB condition (L1=75 dB; L2=75 dB) and -5 dB condition (L1=75 dB; L2=80 dB). When L1 was 65 dB SPL, the largest DPs were obtained across all frequencies for the 5 dB condition (L1=65 dB; L2=60 dB). For L1=55 dB SPL, the largest DPs were obtained across all frequencies for the 5 dB (L1=55 dB; L2=50 dB) and 10 dB (L1=55 dB; L2=45 dB) conditions. No mean DP differences were observed among relative levels (-5 dB to 15 dB) when L1 was 45 dB SPL; however, the 15 dB condition (L1=45 dB; L2=30 dB) at 5531 Hz resulted in fewer identifiable responses than the other relative levels.