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Auditory evoked potential recorders designed for detecting, amplifying and recording the cochlear bioelectric response (i.e., the evoked potential [EP]) to auditory external stimuli. These recorders typically place the electrodes using an invasive method (passing a needle electrode through the tympanic membrane [i.e., transtympanic]) and resting on the cochlear promontory. Or they are noninvasively place against the skin of the ear canal or the surface of the tympanic membrane (i.e., extra-tympanic). Other components of the recorder are signal amplifiers; filters (to suppress interference); memory (e.g., electronic or optical/magnetic disc); and a display. The potentials usually recorded in an electrocochleogram are: (1) an alternating current (AC) voltage that mirrors the waveform of the acoustic stimulus at low-moderate levels of stimulation (i.e., cochlear microphonics); (2) a direct current that reflects the time-displacement pattern of the cochlear partition in response to the stimulus envelope (i.e., the cochlear summating potential; and (3) an AC potential that represents the summed response of the synchronous firing of several thousand auditory nerve fibers (i.e., the auditory nerve Action Potential). Electrocochleographs may include capabilities to deliver external stimuli (e.g., clicks) appropriate to elicit the bioelectric response needed for recording. The recorders are used for diagnosis of specific types of disorders; patients suffering from Meniere\'s disease and/or endolymphatic hydrops often display enlarged summating potentials.
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