Binaural influences on Doppler shift compensation of the horseshoe bat Rhinolophus rouxi

The flying horseshoe bat Rhinolophus rouxi compensates for Doppler shifts i n echoes of their orientation pulses. By lowering the frequency of subseque nt calls the echo's constant frequency is stabilized at the so-called refer ence frequency centered in a narrow and sensitive cochlear filter. This aud io-vocal behaviour is known as Doppler shift compensation. To investigate w hether the bats depend on binaural cues when compensating, three animals we re tested for compensation on a swing before and after unilateral deafening . In each case compensation was severely impaired by unilateral deafening. Individual animals' compensation amplitude was reduced to 28-48% of the pre operational compensation of a +1.8 kHz shift. Doppler shift compensation pe rformance did not recover to control levels during the observed period of 2 4 h after surgery. In contrast, unilateral middle ear removal which induces a unilateral auditory threshold increase of 9-14 dB does not impair compen sation performance on the swing. To mimick Doppler shifts in a fixed setup, the frequencies of recorded echolocation calls were experimentally shifted between 0 and +2 kHz and played back via earphones to six animals. The bat s completely compensated the experimental shifts only as long as the intera ural intensity difference of the playback did not exceed 20 dB. No animal c ompensated with monaural playback.