Measurements of bone-conducted sound in the chinchilla external ear

We measure bone-conduction (BC) induced skull velocity, sound pressure at the tympanic membrane (TM) and inner-ear compound-action potentials (CAP) before and after manipulating the ear canal, ossicles, and the jaw to investigate the generation of BC induced ear-canal sound pressures and their contribution to inner-ear BC response in the ears of chinchillas. These measurements suggest that in chinchilla: i.) Vibrations of the bony ear canal walls contribute significantly to BC-induced ear canal sound pressures, as occluding the ear canal at the bone-cartilaginous border causes a 10 dB increase in sound pressure at the TM (P_TM) at frequencies below 2 kHz. ii.) The contributions to P_TM of ossicular and TM motions when driven in reverse by BC-induced inner-ear sound pressures are small. iii.) The contribution of relative motions of the jaw and ear canal to P_TM is small. iv.) Comparison of the effect of canal occlusion on P_TM and CAP thresholds point out that BC-induced ear canal sound pressures contribute significantly to bone-conduction stimulation of the inner ear when the ear canal is occluded.