5,951 research outputs found
Modelling multiple excitation mechanisms in the cochlea using a 2D finite difference box model
No full textThe cochlea is very versatile. It can be excited by a multitude of mechanisms in order to produce a hearing sensation, even when it is severely malformed. The versatility of the cochlea can also be used to our advantage in the creation of novel methods of cochlear excitation when the conventional pathway is obstructed, for instance through bone conduction hearing aids and excitation via the round window. It is thus important to have an in-depth understanding of the various mechanisms that can cause a hearing sensation and how they are affected by the condition and structures of the cochlea.This thesis investigates the underlying physics associated with various cochlear excitation mechanisms using a 2D finite difference box model. The excitation mechanism examined include; piston-like motion of the stapes, rocking of the stapes, the two inertial components of bone conduction hearing and local excitation of the round window. The model predicts the pressure distribution within the cochlea and allows a direct comparison of the effects of these various excitation mechanisms within the same framework.The effect of the ‘third window’ on the cochlear response due to various cochlear excitation mechanisms was investigated by adapting the model to include the cochlear and vestibular aqueducts. It was found that aqueducts do not affect the cochlear response much for volumetric excitation via the oval window, but were demonstrated to have a significant effect for other excitation mechanisms. In particular it was found that the aqueducts had a large effect when an immobile oval window was modelled, as they allowed a volumetric excitation that significantly increased the response at low frequencies.An air-bone gap has been clinically found in audiograms of patients who have a large vestibular aqueduct, although the reasons for this phenomenon are not fully understood. The effects of a large vestibular aqueduct on the air conduction and bone conduction hearing thresholds have been separately modelled here. It was found that the air-bone gap is predominately caused by the increase of the air conduction hearing threshold due to the internal cochlear pressure forcing fluid through the enlarged aqueduct, reducing the net volumetric excitation
Alice and Cliff Donahue
No full textPhotograph - Friends of Alice B. and William Clifford Donahue, Athabasca, Alberta. Seated, left to right: Cliff Donahue, Joe Mikkelsen, Beryl Mikkelsen, and Marge Logan. Standing, left to right: Don Logan, Alice B. Donahue, Aaron Jones, Lorene Jones, and Beatrice Par
Alice B. Donahue - 09
No full textPhotograph - Alice B. Donahue at flooded campsite on the Athabasca River, Athabasca, Albert
Prediction of inertial effects due to bone conduction in a 2D box model of the cochlea
No full textA 2D box model of the cochlea has been used to predict the basilar membrane, BM, velocity and the fluid flow caused by two components of bone conduction: due to inertia of the middle ear and due to inertia of the cochlear fluids. A finite difference approach has been used with asymmetric fluid chambers, that enables an investigation of the effect of varying window stiffness, due to otosclerosis for example. The BM is represented as a series of locally reacting single degree of freedom systems, with graded stiffness along the cochlea to represent the distribution of natural frequencies and with a damping representative of the passive cochlea. The velocity distributions along the passive BM are similar for harmonic excitation via the middle ear inertia or via the fluid inertia, but the variation of the BM velocity magnitude with excitation frequency is different in the two cases. Excitation via the middle ear is suppressed if the oval window is assumed to be blocked, but the excitation via the cochlear fluids is still possible. By assuming a combined excitation due to both middle ear and fluid excitation, the difference between the overall response can be calculated with a flexible and a blocked oval window, which gives a reasonable prediction of Carhart’s notch
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