Comments on: “The significance of shearing displacements for the mechanical stimulation of cochlear hair cells” (J. Tonndorf)
The purpose of this Comment is to clarify a common misconception pertaining to von Békésy’s data (1953) obtained with the vibrating electrode. Some of these data serve as an important foundation to Dr. Tonndorf’s scheme of cochlear function. We have demonstrated that the microphonic (CM) output of inner hair cells is significantly (30–40 dB) below that of the outer hair cells (e.g. Dallos, 1973). This means that the CM measured from a normal ear is completely dominated by the outputs of outer hair cells. As a consequence, all of von Békésy’s studies utilizing the vibrating electrode reflect the output properties of outer hair cells. Specifically, those results imply that outer hair cells are excited in proportion to basilar membrane displacement, and that the apparent directional sensitivity shown in Dr. Tonndorf’s Fig. 2 (von Békésy, 1960, p.707) reflects the changing excitation of outer hair cells depending on the locus of stimulus application. Thus there is no experimental evidence that would suggest that the inner hair cells are primarily sensitive to longitudinal shear.