A laser interferometer capable of measuring vibrations down to 3 × 10−12 cm was utilized. Basically, a short tube was cemented to the bony wall of the cochlea just apical to the round window, and then a hole was drilled through this tube to expose the basilar membrane. Chemically grown, gold mirrors (approximately 100 μ wide) were dropped onto the basilar membrane using a special probe. The membrane was not touched and the perilymph was not drained. The cochlea was sealed by placing a cap on the tube. Interferometric measurements were carried out through a glass window in the cap. Early measurements showed that the shape of the frequency response of the basilar membrane is similar to that measured by Wilson and Johnstone [J. Acoust. Soc. Am. 51, 705 (1975)] in guinea pigs. Nonlinearities in response were not found. However, both cochlear microphonic measurements and histology showed damage to the cochlea. Experiments were carried out to determine the cause of the damage. Steps were taken to reduce the damage. Measurements on relatively undamaged cochleas are now in progress. [Work supported by NIH.]

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