Fig. 2 . Doppler-shift compensation behavior in response to sinusoidal negative
(below the resting frequency, RF) shifts in the playback frequency. The
frequency of the echo mimics was shifted sinusoidally above (`normal' DSC; A)
or below the bat's resting frequency (`inverse' DSC; B—D) at intensity
levels approximately 60-80 dB above threshold (see
Fig. 1). Each parameter
combination was tested at least 10 times with at least 10 modulation cycles
per bat and experimental session. All data are representative examples
obtained from one bat (RF7). (A) Example of `normal' DSC behavior, i.e.
lowering of call frequencies below RF (circles, bottom trace) in response to
playback frequencies above RF (squares, top trace). For each vocalization
(=event), the call's maximum frequency (circles) and the corresponding
frequency shift introduced in the echo mimic (squares) were determined.
Maximum frequency shift in the echo mimic, +3 kHz relative to RF; modulation
rate, 0.1 Hz, 40 dB attenuation. (B) Example of `inverse' DSC behavior, i.e.
raising of call frequencies above RF (circles, top trace) in response to
playback frequencies below RF (squares, bottom trace). Same conventions as in
A. Maximum frequency shift in echo mimic, -1.5 kHz relative to RF; modulation
rate, 0.1 Hz, 20 dB attenuation. (C) Maximum frequency shift in echo mimic, -3
kHz relative to RF; modulation rate, 0.1 Hz, 20 dB attenuation. (D) Maximum
frequencies of calls relative to RF (ordinate) plotted against the
corresponding playback frequencies relative to RF (abscissa) for three
different maximum frequency shifts (squares, -1.5 kHz; circles, -3 kHz;
triangles, -4.5 kHz; N, number of calls analyzed for three bats).
Modulation rate, 0.1 Hz, 20 dB attenuation. The three curves are the result of
a non-linear regression analysis and are significantly different
(Kruskal—Wallis one-way analysis of variance on ranks;
P<0.001).
