Binaural influences on Doppler shift compensation of the horseshoe bat Rhinolophus rouxi |
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Authors: | O Behrend M Kössl G Schuller |
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Institution: | Zoologisches Institut der Ludwig-Maximilians-Universit?t München, Luisenstr. 14, D-80333 München, Germany e-mail: behrend@zi.biologie.uni-muenchen.de Tel.: +49-89-5902496; Fax: +49-89-5902450, DE
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Abstract: | The flying horseshoe bat Rhinolophus rouxi compensates for Doppler shifts in echoes of their orientation pulses. By lowering the frequency of subsequent calls the echo's
constant frequency is stabilized at the so-called reference frequency centered in a narrow and sensitive cochlear filter.
This audio-vocal behaviour is known as Doppler shift compensation. To investigate whether the bats depend on binaural cues
when compensating, three animals were 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 preoperational compensation of a +1.8 kHz shift. Doppler shift compensation performance did not recover to control
levels during the observed period of 24 h after surgery. In contrast, unilateral middle ear removal which induces a unilateral
auditory threshold increase of 9–14 dB does not impair compensation 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 bats completely compensated the experimental shifts only as long as the interaural
intensity difference of the playback did not exceed 20 dB. No animal compensated with monaural playback.
Accepted: 27 August 1999 |
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