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Department of Speech and Hearing Science
Electrophysiological measures, such as those procedures listed below, play an important role in the assessment of hearing in difficult to test populations, such as very young children, as well as in the differential diagnosis of cochlear versus retrocochlear disorders. These tests are considered objective in that a behavioral response is not required of the patient. Auditory evoked potentials are very small electrical voltage potentials originating from the brain. They are usually recorded from the scalp in response to an auditory stimulus (i.e., clicks, tones, speech sounds, etc.). Evoked potentials are typically recorded using small disk-like self-adhesive electrodes which are stuck on the head and face. The electrodes do not hurt, and they come off easily after completion of testing. A typical recording requires the placement of three or four electrodes. These tests require the use of highly sensitive amplifiers and computer averaging equipment.
These responses are comprised of the cochlear microphonic, the cochlear summating potential and the auditory nerve action potential. This test is useful in intraoperative monitoring and to evaluate possible cases of Meniere's disease.
Auditory Brainstem Response (ABR)These waves originate in the eighth cranial nerve and brainstem auditory structures in the region of lateral lemniscus and inferior colliculus. Auditory brainstem response is used in the neurodiagnosis of eighth nerve or auditory brainstem dysfunction.
Middle (MLR) and Late (LLR) Latency Responses
The middle latency response is from the upper brainstem and/or auditory cortex. The middle latency response is used in the neurodiagnosis of auditory central nervous system disorders above the brainstem level. The late latency response originates primarily in the auditory cortex and is used for frequency specific estimation of hearing sensitivity in cooperative children and adults.
Stacked Auditory Brainstem Response (ABR)
This is a modification of the standard ABR and involves collection of data using click stimuli mixed with high-pass masking noise. This generates activity in virtually all auditory nerve fibers rather than just a subset as in auditory brainstem response.
Vestibular Evoked Myogenic Potentials (VEMP)
This potential is a change in the surface-recorded electromyogram (EMG) that can be evoked over neck and spinal muscles following a high-intensity acoustic input. Vestibular evoked myogenic potentials are important in the evaluation of a patient who is dizzy and can help to determine the origin of the problem.
Cochlear Hydrops Analysis Masking Procedure (CHAMP)
This test is not currently offered at ASU but may be added in the future. It involves looking at the response properties of the basilar membrane for reduced masking effectiveness of high pass noise in an auditory brainstem response when clicks are used. This may be used to establish the presence of cochlear hydrops.