Observing auditory mechanics with pressure and motion measurements

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DESCRIPTION (provided by applicant): Exploring Auditory Mechanics with Pressure and Motion Measurements. The series of experiments proposed here use pressure sensors and other special techniques developed in our lab, complemented by well-established methods like laser-doppler velocimetry, to explore auditory mechanics. The projects of the first four aims continue and extend our previous work on inner and middle ear mechanics. The final aim develops and evaluates a new method for deep cochlear implant insertion. Sound input causes a wave-pattern of sensory tissue motion within the inner ear that is conveyed to the auditory nerve, leading to hearing. This takes place within cochlear compartments having very limited experimental accessibility. Aims one and two of the studies proposed here will push into these barely accessible compartments with specialized micro-sensors. Aim one uses a further miniaturized micro-pressure sensor for in vivo measurements of scala media pressure. Aim two advances our lab's well- established scala tympani pressure measurements by combining them with cochlear microphonic measurements at the same location, within micrometers of the organ of Corti. Both aims are designed to test specific theoretical predictions in order to have a strong impact on the advancement of knowledge. Sound is transmitted by the middle ear with high fidelity even at frequencies where the eardrum has a complex, random-wavy response to sound. Recent theories employ the eardrum wave for sound transmission, and our aim three tests that prediction by changing the wave speed with stiffening agents, measuring the wave speed with a laser velocimeter and also monitoring sound transmission with intracochlear pressure. Our second middle ear aim explores a theoretical prediction that the air cavity behind the eardrum provides reflection that is the basis for good sound transmission at high frequencies. Finally, our last aim explores a novel method for deep cochlear implant insertion using viscous forces. The method will by evaluated physiologically in the proposed studies.