Fig 5 - uploaded by Stefan Stenfelt
Content may be subject to copyright.
The transcranial transmission with the stimulation at the mastoid estimated by three methods. Solid line: hearing thresholds, dotted line: ear canal sound pressure, dashed line: vibration of the cochlear promontory.
Source publication
During the mid 18th century it was found that sound could be transmitted through solids and in the 19th century it was generally accepted that a person can perceive sound by bone conduction (BC). Since then, the research community has tried to understand its fundamental mechanisms. This report provides an overview of the present state in BC physiol...
Context in source publication
Context 1
... transmitted from the mastoid to the contralateral cochlea compared with that transmitted to the ipsilat- eral cochlea was measured by three different methods; (1) mechanical vi- bration of the cochleaea obtained in cadaver heads [11], (2) ear canal sound pressure, and (3) hearing thresholds obtained in live humans. The results are presented in Fig. 5 where the three methods show similar results at fre- quencies above 0.8 kHz; almost monotonically decreasing transmission of -2 dB at 0.8 kHz to -15 dB at 8 kHz. At lower frequencies, the vibration and ear canal sound pressure data are similar whereas the threshold data are almost 7 dB lower at 0.5 kHz. This indicates that both ...
Similar publications
Five different pathways are often suggested as important for bone conducted (BC) sound: (1) sound pressure in the ear canal, (2) inertia of the middle ear ossicles, (3) inertia of the inner ear fluid, (4) compression of the inner ear space, and (5) pressure transmission from the skull interior. The relative importance of these pathways was investig...
Citations
... As a matter of fact, three mechanisms have a noticeable role in this regard which include: Air conduction (AC), Sound induction in skull bone and Sound induction through the soft and hard tissue of body which is finally transmitted to the cochlea. [1][2][3][4] Five factors have been considered as effective parameters in bone conduction include: External auditory canal, Inertia of middle ear ossicle, Inertia of cochlear fluids, Changing in the cochlear space and transmitted pressure via Cerebrospinal fluid (CSF). [3,4] The role of external auditory canal is more obvious in the frequency below than 1000 Hz with occluded external auditory canal since bone conduction gets enhance in low frequency. ...
Bone conduction (BC) threshold depression is not always by means of sensory neural hearing loss and sometimes it is an artifact caused by middle ear pathologies and ossicular chain problems. In this research, the influences of ear surgeries on bone conduction were evaluated.
This study was conducted as a clinical trial study. The ear surgery performed on 83 patients classified in four categories: Stapedectomy, tympanomastoid surgery and ossicular reconstruction partially or totally; Partial Ossicular Replacement Prosthesis (PORP) and Total Ossicular Replacement Prosthesis (TORP). Bone conduction thresholds assessed in frequencies of 250, 500, 1000, 2000 and 4000 Hz pre and post the surgery.
In stapedectomy group, the average of BC threshold in all frequencies improved approximately 6 dB in frequency of 2000 Hz. In tympanomastoid group, BC threshold in the frequency of 500, 1000 and 2000 Hz changed 4 dB (P-value < 0.05). Moreover, In the PORP group, 5 dB enhancement was seen in 1000 and 2000 Hz. In TORP group, the results confirmed that BC threshold improved in all frequencies especially at 4000 Hz about 6.5 dB.
In according to results of this study, BC threshold shift was seen after several ear surgeries such as stapedectomy, tympanoplasty, PORP and TORP. The average of BC improvement was approximately 5 dB. It must be considered that BC depression might happen because of ossicular chain problems. Therefore; by resolving middle ear pathologies, the better BC threshold was obtained, the less hearing problems would be faced.
... The last factor affects dramatically the effectiveness of the outer ear compression mechanism. Ear occlusion boosts the effectiveness of bone conduction in a low frequency range by as much as 30 dB at 100 Hz and 5 dB at 2000 Hz (Stenfelt, 2007). ...
... However, the contribution of the latter mechanism has been questioned recently due to a lack of convincing experimental evidence. For example, clinical findings for otosclerosis and semicircular canal dehiscence cases do not provide support for the presence of this mechanism for frequencies below 4 kHz (Stenfelt, 2007). ...
The hearing system, also called also the auditory system, consists of the outer ear, middle ear, inner ear, and central auditory nervous system. The overall function of the hearing system is to sense the acoustic environment thus allowing us to detect and perceive sound. The anatomy of this system has been described in Chapter 8, Basic Anatomy of the Hearing System. The current chapter describes the function and physiology of the main parts of the hearing system in the process of converting acoustic events into perceived sound. In order to facilitate perception of sound, the hearing system needs to sense sound energy and to convert the received acoustic signals into the electro-chemical signals that are used by the nervous system. A schematic view of the processing chain from the physical sound wave striking the outer ear to the auditory percept in the brain is shown in Figure 9-1. Figure 9-1. A schematic view of the hearing system. The hearing system shown in Figure 9-1 has two functions: sound processing and hearing protection. Sound processing by the hearing system starts when the sound wave arrives at the head of a person. The head forms a baffle that reflects, absorbs, and diffracts sound prior to its processing by the hearing system. The first two sound processing elements of the hearing system are the outer and middle ears that form together a complex mechanical system that is sensitive to changes in intensity, frequency, and direction of incoming sound. Acoustic waves propagating in the environment are diffracted, absorbed, and reflected by the listener's body, head, and the pinnae and arrive through the ear canal at the tympanic membrane of the middle ear. After the acoustic wave strikes the eardrum, its acoustic energy is converted into mechanical energy and carried across the middle ear. At the junction of the middle ear and the inner ear, the mechanical energy of the stapes is transformed into the motion of the fluids of the inner ear and thence into the vibrations of the basilar membrane. The motion of the basilar membrane affects electro-chemical processes in the organ of Corti and results in generation of electric impulses by the array of the hair cells distributed along this membrane. The electrical impulses generated by the hair cells affect the inputs to the nerve endings of the auditory nerve and are transmitted via a network of nerves to the auditory cortex of the brain where the impulses are converted into meaningful perception. A secondary function of the hearing system is to provide some protection for the organ of Corti and the physical structures of the middle ear from excessive energy inputs and subsequent damage by modulating the 9
