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Otoacoustic emissions are sounds generated in the cochlea and recorded in the ear canal that reflect activity of the outer hair cells.

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Otoacoustic emissions can be recorded in quiet, but more commonly are evoked in response to acoustic stimulation. Clicks or tone bursts can be used to elicit transient evoked otoacoustic emissions (TEOAEs). Continuous sinusoidal stimuli are used to evoke distortion product otoacoustic emissions (DPOAEs).

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Otoacoustic emissions can be used to assess the status of cochlear outer hair cells. Specifically, the presence of otoacoustic emissions (either TEOAEs or DPOAEs) is consistent with normal outer hair cell function, and indicates that the individual being tested is likely to have no worse than a mild to moderate sensorineural hearing loss.

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Otoacoustic emissions have also proven to be useful in diagnosing dyssynchrony within the auditory periphery.

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Electrocochleography is a measure of the synchronous response of the auditory nerve to the presence of an acoustic stimulus. It is optimally recorded using an electrode placed on the tympanic membrane or the promontory of the middle ear. Clinical applications include assisting in the differential diagnosis of Meniere’s disease and as a method of assessing the response of the auditory nerve during otoneurologic surgery.

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Auditory brainstem responses (ABRs) are far-field recordings of the synchronized response of neurons within the synaptic relay stations of the auditory brainstem, and can be used to detect impaired neural conduction from various potential neurotologic pathologies.

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The primary application for the ABR in medical settings today is as a tool that can be used to estimate auditory sensitivity in very young or otherwise difficult-to-test populations.

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The auditory steady-state response (ASSR) is an evoked potential that reflects a far-field recording of electroencephalographic activity evoked using continuous sinusoidal stimuli that are either amplitude or frequency modulated.

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The ASSR has emerged as an alternative to tone burst evoked ABR for estimating auditory sensitivity.

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Although less frequently recorded in routine clinical practice, numerous cortical or precortical auditory evoked potentials can be used to assess higher level auditory function. These responses generally require less neural synchrony than the ABR, and as a result have the advantage of being able to be recorded using longer duration, more frequency-specific tonal stimuli or speech.

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Each of the acoustically evoked auditory potentials described in this chapter can also be elicited in response to electrical stimulation provided by a cochlear implant.

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Electrically evoked auditory potentials can be used to assist with the process of fitting the speech processor of the cochlear implant, to help differentiate between cochlear implant failures and lack of neural response in patients who are showing limited or no benefit, and to monitor changes over time in the neural response to electrical stimulation.

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When applied in a strategic manner, the techniques of electrophysiologic recording from the auditory pathology described here provide complementary and highly specific guidance in the clinical assessment of auditory, vestibular, and skull base disorders.