Recording of the cochlear microphonic potential with surface electrodes.

The cochlear microphonic potential was recorded in human subjects with surface electrodes (earlobe clip and scalp vertex disc) and an averaging procedure. Special precautions were taken to identify and separate artefactual, neural and microphonic components. These included shielding of the earphone, a rubber tube to introduce a time delay between artefact and biological response and white noise to mask the neural component. The cochlear microphonic potential was larger in amplitude in response to low frequency sounds and had a high threshold. Two clinical cases of cochlear hearing loss are presented, both lacking neural responses. The cochlear microphonic potential was present in one of them (i.e., neural hearing loss) and absent in the other (i.e., sensory hearing loss).