We propose to extend our studies of cochlear mechanisms in the cat and chinchilla to include direct observation of cochlear partition motion, using the capacitive probe technique of Le Page and Johnstone. We also plan to use the technique to measure motion of the umbo, providing us with information complementary to our recent observations of signals of cochlear origin in the ear canal sound pressure. These new observations are intended to help resolve current controversies regarding cochlear linearity, sharpness of tuning, and vulnerability as seen through invasive direct observations versus non-invasive and indirect techniques. A comprehensive peripheral auditory system model, which incorporates a nonlinear and active two dimensional cochlear mechanical model and a model of the middle ear and acoustic coupler, will be used to interpret experimental results.