Use of frequency modulation combined with amplitude change to elicit frequency-specific whole-nerve response

The averaged whole-nerve response to frequency modulation combined with amplitude change was recorded from the round window of the guinea pig. A downward shift of 20% in the frequency of a 500-Hz, 1-kHz or 2-kHz pure tone with an amplitude increase elicited the responses. The latency for each frequency was investigated at different intensities. The latency is greater for lower-frequency tones and this latency increase agrees well with the traveling wave delay for the intensity range used in this study. A downward shift with an amplitude decrease failed to yield the response. These findings suggest that the response to a downward shift of frequency with an amplitude increase results from new activation due to an apical extension of the envelope of the traveling wave and thus represents the activity in a restricted area of the basilar membrane. Thus, the frequency-modulated tone in downward direction with increased amplitude can be a frequency-specific stimulus.