Efferent olivocochlear bundle: some relationships to noise masking and to stimulus attenuation.

Abstract

The effects of electrical stimulation of the crossed component of the efferent olivo-cochlear bundle (OCB) upon 8th nerve action potentials evoked by clicks presented in broad-band noise were studied. Recordings were taken from round window elec -trodes in anesthetized cats. Action potential reductions due to click attenuation and to noise masking were equated with those produced by OCB stimulation. Both intensity functions and recovery functions for paired clicks are similar for noise masking and for OCB stimulation. Simultaneous presentation of OCB stimulation and noise shows minor summation of effects on action potential amplitudes at low levels and essentially no summation at higher ones. A mechanism for the enhancement of signal-to-noise ratios at the end-organ is implied. Apparently such a mechanism is under central influence.