Review of Whole Head Experimental Cochlear Promontory Vibration with Bone Conduction Stimulation and Investigation of Experimental Setup Effects

Abstract

Bone conduction sound transmission in humans has been extensively studied using cochlear promontory vibrations. These studies use vibration data collected from measurements in live humans, whole cadavers, and severed cadaver heads, with stimulation applied either at an implant in the skull bone or directly on the skin. Experimental protocols, methods, and preparation of cadavers or cadaver heads vary among the studies, and it is currently unknown to what extent the aforementioned variables affect the outcome of those studies. The current study has two aims. The first aim is to review and compare available experimental data and assess the effects of the experimental protocol and methods. The second aim is to investigate similarities and differences found between the experimental studies based on simulations in a finite element model, the LiUHead. With implant stimulation, the average cochlear promontory vibration levels were within 10 dB, independent of the experimental setup and preparations of the cadavers or cadaver heads. With on-skin stimulation, the results were consistent between cadaver heads and living humans. Partial or complete replacement of the brain with air does not affect the cochlear promontory vibration, whereas replacing the brain with liquid reduces the vibration level by up to 5 dB. An intact head–neck connection affects the vibration of the head at frequencies below 300–400 Hz with a significant vibration reduction at frequencies below 200 Hz. Removing all soft tissue, brain tissue, and intracranial fluid from the head increases the overall cochlear promontory vibration level by around 5 dB.

The Impact of Location and Device Coupling on the Performance of the Osia System Actuator

“…Future experiments should also include dynamic force measurements to allow measuring the applied stimulation frequency in each experimental step. That will allow comparing the obtained results more directly with other experimental findings as highlighted in the recent work of Prodanovic and Stenfelt [ 37 ]. In our work, we have employed relative measurements, which do not rely on absolute measurements of stimulation power.…”

Effect of closing material on hearing rehabilitation in stapedectomy and stapedotomy: A finite element analysis

“…Therefore, the promontory accelerance, BF map, and BC hearing loss in otosclerosis were recalculated, as shown in Figure 4 . There are many previous studies on measurement of the promontory accelerance ( Stenfelt and Goode, 2005 ; Eeg-Olofsson et al, 2008 , 2011 ; Håkansson et al, 2008 ; Hakansson et al, 2010 ; Rigato et al, 2018 ; Dobrev et al, 2019 ); Prodanovic and Stenfelt summarized the results of promontory accelerance ( Prodanovic and Stenfelt, 2021 ). Therefore, we compared the calculated promontory accelerance with the experimental results reported by Prodanovic and Stenfelt in Figure 4A , where the calculated accelerance is indicated by the black solid line and the previous experimental results are shown by dashed lines of various colors.…”

Hearing Through Bone Conduction Headsets

“…The deviation between the ipsilateral mastoid and the contralateral stimulations at lower frequencies can be a result of the LiUHead lacking a neck connection. The lack of a neck connection seems to improve the ipsilateral response 5 to 10 dB more at frequencies below 1 kHz compared to the contralateral response ( Prodanovic & Stenfelt, 2021 ). The simulated difference at low frequencies in Figure 5B is therefore also likely affected by the lack of neck connection.…”

“…The simulations are conducted in the finite element model LiUHead that was developed for BC investigations ( Chang et al, 2016 ). The LiUHead has previously been used to evaluate BC sound transmission as measured at the cochlear promontory ( Chang et al, 2016 ; Prodanovic & Stenfelt, 2021 ), BC sound power transmission in the head ( Chang et al, 2018 ), BC hearing aids ( Chang & Stenfelt, 2019 ), effects of mastoidectomy on BC sound ( Prodanovic & Stenfelt, 2020 ), and BC transmission with stimulation applied at soft tissue positions ( Stenfelt & Prodanovic, 2022 ). Details of the original LiUHead can be found in Chang et al (2016) and additional modifications are presented here.…”

“…It also simulates the BC transducer at the mastoid position in the experimental part of the current study. The mechanical parameters of the soft tissue between the circular plate and the skull bone (orange in Figure 1B ) were altered to account for a 5.4 N static force according to the method presented in Chang and Stenfelt (2019) and Prodanovic and Stenfelt (2021) . The frontal position simulates the application of a typical BC headset and the interface used here is the same as in the Aftershokz Aeropex (us.aftershokz.com).…”