Gender effects on high frequency distortion product otoacoustic emissions in humans

Gender has been reported to affect many tests of the auditory system, including distortion product otoacoustic emission (DPOAE) group delay and level when elicited with lower frequency stimuli (<8 kHz). Using custom equipment, the effect of gender on DPOAEs at higher frequencies was explored. It is expected that differences in group delay reported at very low frequencies (e.g., 0.78 Hz) will not be replicated at higher frequencies. Additionally, it was hypothesized that female subjects would display larger-level DPOAEs at higher frequencies, based on evidence that female subjects tend to have larger emissions when elicited with lower frequency stimuli.

DPOAEs were measured in 37 subjects (20 females and 17 males) with normal behavioral thresholds, middle ear function, and present acoustic reflexes at 1 kHz with contralateral stimulation. Behavioral thresholds were measured through 16 kHz using Békèsy tracking. Ratio and frequency sweeps were used to calculate DPOAE group delay and measure DPOAE levels, respectively. Ratio sweeps were obtained at f2 frequencies of 1, 2, 4, 8, 10, 12, 14, and 16 kHz, with L1 = 60 and L2 = 45 dB SPL, with the ratio (f2/f1) varied from 1.11 to 1.3. Frequency sweeps were measured with L1 = 60 and L2 = 45 dB SPL and an f2/f1 of 1.2 at discrete f2 frequencies between 1 and 16 kHz. Data were subjected to repeated-measures analysis of variance.

Significant frequency-by-gender interactions were found for group delay (for data from 1 to 8 kHz) and level (for data from 9 to 15 kHz). The frequency-by-gender interaction and the main effect of gender were not significant for the behavioral results.

Gender-based norms for auditory-evoked potentials measures are standard in clinical settings. The results of the present study, in agreement with previous studies, indicate that significant interactions exist between gender and DPOAE group delay values in the lower frequencies, and between gender and DPOAE levels at the higher frequencies. To reach the goal of using high frequency DPOAEs in clinical protocols, such as for auditory neuropathy/dys-synchrony diagnosis and ototoxicity monitoring, DPOAEs elicited with conventional and higher frequency stimuli must be understood, including the role of gender to determine if an effect on clinical protocols would exist.