Using auditory steady-state responses for measuring hearing protector occlusion effect.

INTRODUCTION: The currently available methods for measuring the occlusion effect (OE) of hearing protection devices (HPDs) have limitations. Objective microphonic measurements do not assess bone-conducted sounds directly transmitted to the cochlea. Psychophysical measurements at threshold are biased due to the low-frequency masking effects from test participants' physiological noise and the variability of measurements based on subjective responses. An auditory steady-state responses (ASSRs) procedure is used as a technique that might overcome these limitations.

PARTICIPANTS AND METHODS: Pure-tone stimuli (250 and 500 Hz), with amplitude modulated at 40 Hz, were presented to twelve adults with normal hearing through a bone vibrator at three levels in 10-dB steps. The following two conditions were assessed: the unoccluded ear canal and occluded ear canal. ASSR amplitude data as a function of the stimulation level were linearized using least-square regressions. The ASSR-based "physiological" OE was then calculated as the average difference between the two measurements.

RESULTS: A significant statistical difference was found between the average threshold-based psychophysical OE and the average ASSR-based OE.

CONCLUSION: This study successfully ascertained that it is possible to objectively measure the OE of HPD using ASSRs collected on the same participant both with and without protectors.