Bone-Conducted Sound: Physiological and Clinical Aspects

Abstract

Five factors contributing to bone conduction hearing have been identified: 1) sound radiated into the external ear canal, 2) middle ear ossicle inertia, 3) inertia of the cochlear fluids, 4) compression of the cochlear walls, and 5) pressure transmission from the cerebrospinal fluid. Of these five, inertia of the cochlear fluid seems most important. Bone conduction sound is believed to reflect the true cochlear function; however, certain conditions such as middle ear diseases can affect bone conduction sensitivity, but less than for air conduction. The bone conduction route can also be used for hearing aids; since the bone conduction route is less efficient than the air conduction route, bone conduction hearing aids are primarily used for hearing losses where air conduction hearing aids are contraindicated.

Estimation of bone conduction skull transmission by hearing thresholds and ear-canal sound pressure

“…At the higher frequencies, above 2 kHz, there was a general trend of lower ECSP occlusion effect values when compared with the threshold based occlusion effect for all three stimulation positions (Table 3). This was due to the reduction of ECSP caused by the occlusion at higher frequencies, while perception of BC sound was not influenced by occlusion (and therefore insensitive to the decrease in ECSP) due to the contribution of other BC pathways to stimulus perception (Stenfelt and Goode, 2005b;Stenfelt and Reinfeldt, 2007).…”

“…It has been shown that the ossicles' vibration is higher when the stimulation is in line with the lowfrequency vibration direction of the ossicles than for the perpendicular directions (Stenfelt et al, 2002). Also, it has been suggested that the ossicles can contribute to the perceived BC sound in the 2 to 3 kHz frequency range (Stenfelt and Goode, 2005b;Stenfelt, 2006). Consequently, the difference seen at 3 kHz, and to some extent at 2 kHz, may be due to the contribution of the ossicles when the stimulation was at the ipsilateral mastoid compared to less or nonexistent ossicle contribution when the stimulation was at the other positions.…”

“…One possible problem with the idea of cochlear vibration being directly related to perception of BC sound is that BC perception is not a single phenomenon but caused by several mechanisms, all contributing to the final BC perception (Stenfelt and Goode, 2005b;Stenfelt, 2011;Tonndorf, 1966;von Békésy, 1960). Even if the ultimate excitation in the cochlea is a traveling wave on the basilar membrane (Stenfelt et al, 2003b;Stenfelt, 2007;von Békésy, 1932), there are contributors that may not be directly related to the vibration of the cochlea.…”

Cochlear boundary motion during bone conduction stimulation: Implications for inertial and compressional excitation of the cochlea

“…A sound transmitted by bone conduction travels via different pathways after becoming a vibration of the skull bone or soft tissues. Five pathways have been identified as the most important for BC sound perception in the normal hearing human including sound pressure generation in the ear canal, inertial forces of the middle ear ossicles, inertial forces acting on the cochlear fluid, alteration of the cochlear space, and sound pressure transmission from the skull interior [10]. The relative importance of these pathways has not been clarified.…”

Simulation of bone-conducted sound transmission in a three-dimensional finite-element model of a human skull

“…Considered as the main medium of the sound wave vibration, the skull transmits the BC sound from the source to the cochlea. The inertia of the cochlear fluids and alteration of the bony shell surrounding the cochlea in human skulls are the most significant factors causing the BC hearing [8]. The transmission performance of the skull is affected by its anatomy, geometry, composition, and mechanical properties of the structures.…”