Temporal patterns of the responses of auditory-nerve fibers to low-frequency tones

The temporal response patterns of auditory-nerve fibers to low-frequency tones were studied in anesthetized cats using period histograms. 'Peak-splitting' was observed mostly in fibers with lower characteristic frequencies (CF < 2 kHz) and with lower-frequency stimulation (< or = 500 Hz). The occurrence of peak-splitting, the number of peaks, and the time between the peaks were all dependent upon the stimulus frequency. The phases of responses, although complex functions of stimulus frequency, intensity, and the fiber's CF, clearly showed traveling-wave characteristics for all frequencies at or above 100 Hz. The amount of phase change with intensity was generally small for lower-frequency stimuli (< approximately 50 degrees), although larger phase changes (e.g., approximately 180 degrees) were occasionally seen with higher-frequency stimuli. At 50 and 100 Hz, the phase of neural responses in the basal region roughly corresponds to the maximum velocity of the basilar membrane towards scala tympani (as inferred from cochlear microphonic recordings).