Some dualistic properties of the cochlear microphonic.

Within a small frequency range just above the characteristic frequency of a differential electrode pair, cochlear microphonic input-output functions are bimodal, exhibiting two maxima. The more sensitive, low-intensity response has a more limited linear operating range, and it is more labile due to acoustic fatigue or hypoxia. After fatigue or hypoxia, the high-intensity response is revealed. The latter operates 180 degrees out-of-phase with the former, presumably due to its being generated more basalward in the cochlea. The difference in the lability of the two components suggests that the two sources are different types of hair cells: i.e., outer and inner hair cells.