SHEARING MOTION IN THE HEARING ORGAN MEASURED BY CONFOCAL LASER HETERODYNE INTERFEROMETRY

To investigate the presence of the postulated shearing motion in the m icromechanics of the inner ear during sound stimulation we measured th e vibratory response of the tectorial membrane and the reticular lamin a in the third cochlear turn in an isolated temporal bone preparation using confocal laser heterodyne interferometry. The mechanical respons e of the tectorial membrane had the same frequency of maxima as the un derlying reticular lamina, but was not as sharply tuned. When the two- dimensional motion was calculated from measurements made from several viewing angles it was found that the vibration of the reticular lamina had significant components both normal and tangential to its surface. The tectorial membrane motion, however, was primarily in a direction approximately perpendicular to the surface of the reticular lamina. Th e results indicate that shearing motion is produced predominantly by t he radial motion of the reticular lamina.