Biasing of the summating potentials.

Summating potentials (SP) were recorded in the guinea pig cochlea, utilizing the differential-electrode technique. The effects of biasing the cochlear partition of the SP were observed under three different conditions: 1. electrical biasing--direct current polarization: 2. stimulus biasing--mechanical bias induced by low frequency sound stimulation, 3. COCB biasing--electrical stimulation of the crossed olivo-cochlear bundle. All three forms of biasing were found to have similar ellects on the SP which can be described in terms of the "absolute direction of change" in the potential. Under negative current (scala vestibuli negative; scala tympani positive), the negative phase of the stimulus bias (deflection of the cochlear partition towards scala vestibuli), or stimulation of the COCB, the SP is made more positive or less negative, as the case may be. In other words, the negative component of the differentially recorded SP is depressed, wheras the positive component is enhanced. The dominant influence os all three forms of biasing appears to be on mechanoelectric distortion arising in the hair-cell transduction process.