Masked cochlear whole-nerve response intensity functions altered by electrical stimulation of the crossed olivocochlear bundle.

Cochlear whole-nerve response (CAP) intensity functions were recorded from the guinea pig round window. The intensity functions were obtained in the presence of masking noise, with electrical stimulation of the crossed olivocochlear bundle (COCB), and the combination of masking noise and COCB stimulation. Electrical stimulation of the COCB produced the expected reduction of CAP magnitude for low- to moderate-intensity tone bursts. Masking noise produced reductions in CAP magnitude over the whole signal intensity range used in this study. The combination of electrical stimulation of the COCB with the masking noise produced CAP magnitude changes graded between reduction and enhancement dependent on signal and masker levels. In general, at low signal levels, the masked CAP magnitude is reduced compared to the masked alone condition. At high signal levels, the masked CAP is increased in magnitude. These results confirm and extend the earlier observations of Nieder and Nieder [Exp. Neurol. 28, 174-188 (1970); also, Nature 227, 184-185 (1970)].