EFFECTS OF ELECTRICAL BIASING ON ELECTRICALLY-EVOKED OTOACOUSTIC EMISSIONS

Electrically-evoked otoacoustic emissions were produced using a 10 mu A, 750 Hz AC current plus a biasing DC current in the range of +/- 10 mu A. Concurrently, a 1643 Hz tonal stimulation was delivered to the e ardrum. At low sound levels, negative DC current increased the emissio n while positive DC current reduced the emission. Such findings are re asonably explained by a negative-feedback model of cochlear function. At high sound levels, negative DC current reduces the emission, while positive current has little effect. These data can be accounted for by voltage-dependent length changes shown to occur in isolated outer hai r cells, with the additional requirement that voltage-dependent K+ cha nnels in outer hair cells reduce the effectiveness of positive DC curr ent in changing membrane potential.