Evoked potentials in cat auditory nerve: Suppression by prior tonal stimulation

Action potentials (AP) recorded from the eighth nerve of a cat to a tone pip, S₁, were suppressed when preceded by a monotic or dichotic conditioning tone, Tc. The suppression increased when (1) the interval between Tc and S1 was decreased, (2) either the intensity or the duration of Tc was increased, or (3) the difference in frequency between the two stimuli was reduced. Thus the nerve action potential amplitude correlates strongly, but inversely, with the loudness enhancement effects seen in man (Galambos, Bauer, Picton, Squires & Squires,Journal of the Acoustical Society of America, 1972, 52). Since Coats and Dickey (Journal of the Acoustical Society of America, 1972, 52) found that the human AP can be diminished by a preceding noise without reducing the loudness of a click, the available results suggest that a central mechanism functions to compensate for the reduction in AP amplitude. The dichotic effects could be accounted for by cross-hearing, thereby providing no evidence for a role of the olivocochlear bundle in the effects observed.