Peripheral auditory tuning for fine frequency analysis by the CF-FM bat,Rhinolophus ferrumequinum

SummaryRhinolophus ferrumequinum compensates for Doppler shifts and keeps the frequency of the CF-portion of echoes constant at a reference frequency. The bat's cochlea is specialised for the detection of sounds in a narrow range including this reference frequency. The threshold curve of the N1-on (summated activity of primary auditory neurons evoked at the onset of a tonal stimulus) has a sharp notch about 24–30 dB deep which is exactly tuned to the reference frequency. N1-off is most prominent at stimulus frequencies 0.5–1 kHz below the reference frequency. In this frequency range the envelopes of the CM (cochlear microphonics) have slower rise and decay times than the stimulus envelopes. A comparison of our physiological data with the morphological data of Bruns (1976a, b) leads to the suggestion that the cochlea acts as a narrowly-tuned mechanical filter which is responsible for sharp tuning of the CM, N1-on and N1-off threshold curves.