Studies on the so-called central frequency of narrow-band action potential of the cochlea

Studies were made on the factors determining the so-called central frequency of narrow-band action potentials of the cochlea of the guinea pig. Specific attention was paid to the effects of changing intensities of masking noises on the central frequency. Compound action potentials were recorded by applying simultaneous click stimuli with a masking noise supplied through a high-pass filter. Narrow-band action potentials were derived by setting the cutoff frequencies of the filter to an octave band width. The derived responses showed a prolongation in latency when the intensity of the masking noise was increased. The results were analyzed on the assumption that the band pass characteristics of the high-pass filter would act as a determinant of the frequency range at which the responses attained the maximal heights. The assumption predicts that an increase in intensity of masking noise induces a shift of the central frequency toward a lower frequency range, which leads to a prolongation of the response latencies. Discussion is also made on the shift of the central frequency due to a rise of threshold for hearing.