A mechanical lumped-element model of the human middle ear for bone conduction hearing.

Bone conduction (BC) is an important modality of hearing. It enables us to differentiate conductive and sensorineural hearing loss, perceive sounds despite a disabled middle ear, and listen to conversation and music privately without blocking the ear canal. Yet the mechanism underlying BC is not fully understood mainly because the bone-conducted vibrations in the skull simultaneously stimulate the outer ear, the middle ear, and the cochlea. The nature of the parallel stimulation on those interconnected parts makes it difficult to contemplate the dynamics in each compartment and the influences they impose on each other. In the present study, a computational lumped-element human ear model for BC is developed. The model comprises lumped mechanical components-masses, springs and dampers-to represent structures such as eardrum, ossicles, ligaments, joints, and cochlear fluid. The parameters of those components are determined by fitting the simulated ossicular vibrations to the measured counterparts reported by Stenfelt et al., the most extensive BC middle-ear dataset. The results show that the model-predicted vibrations of the umbo and stapes generally match the experimental results not just in the normal ear condition (with a fitting error of 1.8 dB and 3.9 dB, respectively, for the umbo and stapes) but also after various perturbations such as adding mass on the eardrum and separating the incudostapedial joint (with fitting errors ranging from 1.3 to 10 dB). It is believed this is the first lumped-element model that can correctly simulate the vibrations of the human middle ear in BC. The model can serve as the bedrock not only for better understanding the dynamics of the entire ear in BC but also for developing new diagnostics for middle-ear conditions and assisting design of novel hearing prostheses.