Abstract
Bone conduction (BC) hearing devices have been used to improve hearing in patients with unilateral conductive hearing loss; however, the clinical results of improvement in the sound localization ability are still controversial. Transcranial transmission in BC may be an important factor affecting sound localization abilities. Transcranial or interaural attenuation, derived from energy attenuation during the BC process, is determined by the different transfer functions of multiple pathways and affected by the whole-head vibration modes. The purpose of this study is to analyze the frequency dependence of BC vibration modes of the whole head, the contribution of middle and inner ear pathways to BC hearing, and the relationship between transcranial attenuation results by dynamics measurement and hearing thresholds. Experimental studies of vibration modes and transcranial attenuation characteristics in BC are performed using scanning laser Doppler vibrometry (LDV) measurements on human cadaver heads. Differences in vibration modes between the excitation and contralateral sides are observed. Additionally, a multiscale human whole-head FE model, including the skull, bony outer ear, ossicular chains, and bony inner ear structures, is proposed to study the mechanism of BC in the human hearing system. After verifying the rationality of the FE model using mechanical impedance and frequency response data, the transcranial attenuation on the temporal bone surfaces and the middle ear structure is calculated in the FE model. Moreover, the vibration characteristics of bilateral ossicular chains and the cochlear bony wall are observed in the whole-head FM model to study their contributions to BC hearing. By analyzing the experimental and numerical results of the vibration modes and the frequency response of the whole head incorporating the ossicular chain and cochlear bony wall, the intrinsic relationship between the results of transcranial attenuation by 1D LDV, 3D LDV, and hearing threshold measurements is further investigated.
Highlights
Bone conduction devices (BCDs) can convert received sound into mechanical vibration; subsequently, the vibration is transmitted to the inner ear, thereby stimulating hair cells and producing auditory signals [1, 2]
We investigate the frequency dependence of bone conduction (BC) vibration modes, the middle and inner ear contribution to BC hearing, and the relationship between transcranial attenuation results measured by 1D and 3D laser Doppler vibrometry (LDV) and hearing thresholds
Measuring or calculating (FE models) the transcranial attenuation at the surface of the skull would be inadequate to study the contribution of the middle ear structure in the BC mechanism. e multiscale human whole-head finite element (FE) model, compared with previous FE models which focused on the human skull and surrounding soft tissues [25, 26, 33], was embedded with the miniature middle ear and inner ear structures. erefore, the new FE model could provide more direct measurements of the frequency responses of the ipsilateral and contralateral tympanic membrane (TM) or stapes footplate, which was strongly associated with the perception of the BC sound
Summary
Bone conduction devices (BCDs) can convert received sound into mechanical vibration; subsequently, the vibration is transmitted to the inner ear, thereby stimulating hair cells and producing auditory signals [1, 2]. One purpose of unilateral BCD implantation for patients who have unilateral hearing loss is to form spatial hearing by cooperating with the healthy ear, thereby improving the abilities of sound localization and speech recognition in noise [3, 4]. Unlike the significantly improved sound localization abilities of patients who have bilateral conductive hearing loss through using bilateral BCDs, the clinical effectiveness is still controversial for unilateral hearing loss patients using unilateral BCDs [5,6,7]. Unlike AC, BC energy can transmit to the contralateral ear with small attenuations through wholehead vibration, which is called BC transcranial or interaural transmission, resulting in interference with AC hearing
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