Cochlear Modelling
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- Category: Biophysical Research
- Last Updated on Tuesday, 11 December 2012 09:15
- Written by Editorial Board
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In this section you can find two types of information : (1) Brief descriptionsof recent developments in cochlear modeling, related more to the OAE function than to the physiological structure of the cochlea; (2) Brief comments on issues related to cochlear functionality.
Recent Developments
From the May -June 2002 Editorial
The traditional categorization of OAEs often divides them simply into two categories based upon the stimulus parameters needed to evoke the specific classes of OAEs (Probst et al 1991). For example, spontaneous OAEs (SOAEs) are in a class of their own in that no stimulus is required to evoke these emissions. Transient-evoked OAEs (TEOAEs), stimulus-frequency OAEs (SFOAEs), and DPOAEs are placed in the other category referred to as the stimulus-evoked emissions in that all these OAEs are elicited by applying deliberate acoustic stimulation to the ear. A major limitation of this simple classification scheme is that little information is provided about the mechanisms of generation for the unique subtypes of OAEs. Generally, under this schema, all OAEs are assumed to arise from the same nonlinear mechanical workings that underlie cochlear processing (eg, Kemp 1978; Kemp & Brown 1983). Recently, Shera and Guinan (1999) presented a taxonomy for mammalian OAEs that can be experimentally verified (Kalluri & Shera 2001). In this conceptualization, Shera and Guinan (1999) proposed that OAEs arise from two fundamentally different mechanisms. Thus, there are OAEs that arise by linear reflection and those that are generated by nonlinear distortion. This distinction forms a 'family tree' of OAEs in which TEOAEs, SFOAEs, and SOAEs are based upon linear reflections, whereas DPOAEs are produced mainly from nonlinearities acting as emission sources. This classification system is extremely useful in that OAEs can be categorized based upon their mechanisms of generation. Thus, the familiar click-evoked TEOAEs come from reflection off of pre-existing micromechanical impedance perturbations, distributed along the organ of Corti, which might include such conditions as disorganized outer hair cell (OHC) arrays (eg, Lonsbury-Martin et al 1988), that are unique to each cochlea. On the other hand, DPOAEs arise primarily from nonlinear elements in the cochlea that are stimulated by the in-coming traveling waves. What is most important to realize is that OAEs recorded in the ear canal, especially in humans, are rarely due purely to one form or the other, but represent a mixture of the two emission sources.
Recent Comments
07/04/2004
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