THE EFFECT OF SOUND INTENSITY ON F(1)-SWEEP AND F(2)-SWEEP DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS PHASE DELAY ESTIMATES IN HUMAN ADULTS

Phase measurements of distortion product otoacoustic emissions (DPOAE) provide an estimate of round-trip travel times in the cochlea. This s tudy examined differences in f(1)- and f(2)-sweep round-trip delays es timated from DPOAE phase responses in 20 normal-hearing adult human su bjects as a function of f(2) frequency and sound intensity. Eight diff erent f(2) frequencies ranging from 1.1-13 kHz were presented. For bot h the f(1)- and the f(2)-sweep stimulation conditions the f(2)/f(1) ra tios were between 1.1 and 1.3. Primary intensity levels for f(2) were varied in 5-dB steps from 30-50 dB SPL (where f(1) was 15 dB>f(2)). De lays in the f(2)-sweep condition were equal to or longer than travel t imes in the f(1)-sweep condition. Round-trip delays showed a significa nt intensity dependence in both the f(1)- and f(2)-sweep conditions (p less than or equal to 0.01). In both conditions, the delay increased as stimulus intensity decreased. Delay estimates in the f(2)-sweep con dition were more strongly intensity dependent than estimates in the f( 1)-sweep condition at f(2) frequencies above 1.6 kHz. The mean differe nce in f(2)- and f(1)-sweep delays at low intensities ranged from 15.9 periods at the 9.2 kHz f(2) place, to 2.5 periods at the 1.6 kHz f(2) place. The intensity dependence of round-trip delay estimates in both conditions may be attributed to intensity-dependent changes in the co chlear filter response time related to the sharpness of tuning of DPOA E responses. The steeper intensity dependence and longer delays observ ed in the f(2)-sweep condition may similarly be attributed to a greate r proportion of the f(2)-sweep response being composed of the filter r esponse time. (C) 1997 Acoustical Society of America.