An examination of gender differences in DPOAE phase delay measurements in normal-hearing human adults

This study examined gender differences in f(1)- and f(2)-sweep distortion product otoacoustic emission (DPOAE) phase delay measures in 60 normal-hearing human adults. Phase delay measures were obtained at six different f(2) frequencies ranging from 1.1 to 6.0 kHz (f(2)/f(1) ratios were 1.1-1.3). Primary levels for f(2) were 45 and 50 dB SPL (f(1)f(2)). Gender differences have been observed in normal-hearing human adults in both auditory brainstem response (ABR) and f(1)-sweep DPOAE studies. Gender differences in delay have been attributed to differences in the average length of the cochlea, where female cochleas are 13% shorter than male cochleas. Previously, the authors have proposed that the f(1)-sweep phase delay estimate is predominantly composed of a level-independent transport time to the site of DPOAE generation and a small proportion of the level and frequency-dependent filter build-up time. The f(2)-sweep delay also contains the transport time, however, it is predominantly composed of the filter build-up time. Therefore, delay differences between stimulation paradigms are equal to a proportion of the filter build-up time. In this study, mean f(1)- and f(2)-sweep delays were significantly longer in male ears than female ears at 1.1 kHz (45 and 50 dB). At 50 dB, f(1)-sweep phase delay measures were 18% longer in male ears (6.5 ms) than female ears (5.5 ms). Mean f(2)-sweep delays were 23% longer in male ears (10.0 ms) than female ears (8.1 ms). This gender difference was not observed when the isolated filter build-up time was calculated from the DPOAE phase delay difference. These observations may therefore be attributed to a gender-related anatomical difference in cochlear length.