basics







Contents of this section: Introduction


The Transient evoked otoacoustic emissions (TEOAEs) are the objective evidence of function of the cochlear mechanism. This implicates also normal function of the middle ear.

The terms "TEOAE" and "CEOAE" they both refer to a OAE response evoked by a click. Although the term "CEOAE" is more appropriate because indicates that the OAE response is evoked by a click stimulus, in the majority of the studies in the literature the term "TEOAE" is used.

The TEOAE responses are properties of normal ears. The generation mechanism is not fully understood yet, but a number of studies have presented evidence supporting that the TEOAEs are generated by a reflection of the travelling wave at micromechanical impedance perturbations in the Organ of Corti (Kemp, 1980). The TEOAEs can be also recorded from other animal species, used in clinical research, such as mice, rats, guinea pigs, chinchilla, rabbits, dogs, and monkeys. As it might be expected aging processes affect the amplitude and frequency content of the responses.
        The fact that we have categorized the OAEs in various types (i.e, TEOAEs, DPOAEs, SOAEs, SFOAEs) does not automatically imply that the generation OAE mechanisms are as many. There are studies which have reported that the different types of OAEs influence each other, and a typical example is how the SOAE peaks enhance the TEOAE spectrum. In addition, a number of papers (Yates and Withnell, 1999; Withnell and Yates , 1998; Withnell et al, 1998; 2000) have underlined the relationship between distortion product otoacoustic emissions and TEOAEs where high frequency components of click stimuli generate low frequency DPOAEs.
        The last few years the relationship of these types of OAEs have been attributed to the presence of two distinct cochlear mechanisms which gave rise to a different OAE taxonomy not in terms of the evoking stimulus , but in terms of the generation mechanism. Shera and Guinan (1999) postulated that the signals we commonly record, are the cumulative results of nonlinear processes (DPOAEs) and reflection mechanisms (TEOAEs). This hypothetical structure is known as the two source interference model. This theoretical foundation has been succesfully applied to distortion product otoacoustic emissions (Talmadge et al, 1999).

References:

Kemp DT 1980. Towards a model for the origin of cochlear echoes. Hear Res. 2, 533-548

Talmadge CL, Long GR, Tubis A, Dhar S, 1999. Experimental confirmation of the two-sourse interference model for the fine structure of distortion product otoacoustic emissions. J. Acoust. Soc. Am. 105, 275-292

Withnell RH and Yates G, 1998. Enhancement of the transient-evoked otoacoustic emission produced by the addition of a pure tone in the guinea pig. J Acoust Soc Am .104:344-349.

Withnell RH, Kirk D, Yates G, 1998. Otoacoustic emissions measured with a physically open recording system. J Acoust Soc Am.104:350-355.

Withnell RH, Yates GK, Kirk DL, 2000. Change to low frequency components of the TEOAE following acoustic trauma to the base of the cochlea. Hear Res. 139, 1-12.

Yates GK and Withnell RH , 1999. The role of intermodulation distortion in transient evoked otoacoustic emissions. Hear Res. 136, 49-64.