Human frequency-specific whole-nerve response by use of frequency-modulated tone

Based on the results of animal experiments performed previously, a human study of the compound action potential (AP) to frequency-modulated (FM) tone was achieved, using the transtympanic electrode, in order to obtain frequency-specific APs. Clearly recognizable responses were elicited by a downward shift of 20% in the frequency of a 515-, 1 150- or 2 230-Hz pure tone (with a slight amplitude increase). The latency for each frequency was investigated at different intensities. The latency is greater for lower-frequency tones and, as in the animal experiments, this latency increase agrees with the traveling delay for the intensity range used in this study. The latency-intensity curves of the three frequencies do not tend to converge with increase in the intensity of the tone. The latency at moderate intensity is similar to that for the short tone burst at threshold intensity. These findings suggest that the FM tone in downward direction can be a frequency-specific stimulus even at relatively high intensities. Combined use of the tone burst (low intensity) and this FM tone (high intensity) may be useful in clinical tests.