Coding of Sinusoidally Frequency-Modulated Signals by Single Cochlear Nucleus Neurons of Rhinolophus ferrumequinum
The Greater Horseshoe bat, Rhinolophus ferrumequinum, emitts a long constant-frequency (CF-) component of about 83 kHz during echo-location. The echoes are Doppler-shifted upward in frequency due to the realative movement between bat and target. The bat compensates for these deviations in the echo-frequency by lowering the frequency of the emitted call so that the echo-frequency remains constant within a narrow frequency band (Schnitzler, H.-U., 1968; Schuller et al., 1974). The wing beat of prey insects results in periodic frequency and amplitude modulations of this carrier frequency which can be used by the bats as clues for detection and probably identification of moving prey objects. Neurophysiological investigations of the inferior colliculus (IC) and auditory cortex of Rhinolophus (Schuller, G., 1979; Ostwald, J., this volume) showed that the sharply tuned filterneurons around 83 kHz specifically analyse the information contained in periodic modulations.
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