The goal of this study is to assess the predictive value of distortion product otoacoustic emissions (DPOAEs) to identify physiologic changes in hair cell function in humans exposed to acoustic overstimulation. It is hypothesized that acoustic overstimulation will result in decreased amplitude of DPOAEs. Noise exposure is known to cause a temporary decrease in hearing which appears to share common changes in cochlear physiology, such as temporal growth and recovery patterns. Resonant frequency of the outer ear has also been implicated in incidence of the temporary hearing loss. The secondary hypothesis states that the frequencies at which DPOAEs show maximum amplitude decrease, correspond to the resonance characteristics of the outer ear. Twelve volunteers with normal hearing between the ages of 18-25 years were selected without respect to gender or race. One ear will be randomly selected; the opposite will be protected with a noise- attenuating plug. Octave-band noise centered at 2.83 kHz will be delivered to the eardrum at 105 dB SPL for 10 minutes. DPOAE input- output functions will be examined at six frequencies prior to and immediately after noise exposure. DPOAE thresholds and growth functions will be analyzed and compared between pre- and post-exposure conditions. Hearing will be monitored throughout the experiment as a safety measure only.
