THE VIBRATION PATTERN OF THE HEARING ORGAN IN THE WALTZING GUINEA-PIGMEASURED USING LASER HETERODYNE INTERFEROMETRY

The mechanical tuning characteristics of the hearing organ were measur ed in response to sound stimulation using laser heterodyne interferome try in in vitro preparations of temporal bones from waltzing guinea-pi gs expressing different degrees of hearing organ and sensory cell dege neration. Measurements were made at various stages of structural chang es allowing us to correlate structure and mechanical function. It was found that the characteristic frequency of the response at a given loc ation in the cochlea occurred at lower frequencies than what is normal ly seen and that the sharpness of the mechanical tuning was considerab ly reduced when sensory hair cells were absent and the hearing organ s tructurally altered. However, even when extensive hair cell degenerati on was evident a residual mechanical tuning was present. These results further support the concept that the sensory hair cells play a key ro le in determining normal auditory tuning characteristics. It is sugges ted that the basilar membrane mechanics gives rise to a broadly tuned mechanical response on which a sharper tuning mechanism, originating f rom the hair cells, is superimposed.