Fig. 3. Doppler-shift compensation behavior in response to stepwise changes in the
frequency of echo mimics. (A) Time courses of the frequency shift in echo
mimics (white circles, bottom trace) and corresponding call frequencies (black
circles, top trace; only the highest frequency measured in each call is
given). An initial positive shift in playback frequency causes playback
frequencies to rise above the resting frequency (RF). Call frequencies are
therefore lowered below RF. The subsequent negative step back to zero shift
causes playbacks to return at frequencies below RF (since call frequencies are
still below RF). Consequently, the bat increases its call frequencies. Each
step was maintained for up to 30 s until the bat had reached its compensation
frequency. At least 10 repetitions of each parameter combination were
presented per bat and session. Time constants were determined by measuring the
time until the call frequency had changed by 67% in response to positive and
negative shifts in stimulus frequency. (B) Time courses of call frequency
increases (3 kHz above RF) in response to negative steps in playback frequency
to zero shift for two different attenuations (bat dsb6). Each symbol
represents the maximum frequency in one call. Louder playback signals (0 dB
attenuation, open circles; N=226) cause call frequency to increase
faster than weaker playback signals (30 dB attenuation, filled circles;
N=103). The difference between the two conditions is significant (all
pairwise multiple comparison procedure, Dunn's method, P<0.05).
Frequency shifts of 1.5 kHz and 4.5 kHz above RF yielded similar results (not
shown). (C) Mean time constants for call frequency increases analyzed in all
three bats tested in response to negative steps in playback frequency.
N is the number of time constants analyzed. The numbers of calls
analyzed for each condition were 366 (0 dB), 354 (10 dB), 292 (20 dB) and 169
(30 dB). Significant differences exist for 0 dB versus 20 dB and 30
dB, for 10 dB versus 20 dB and 30 dB and for 20 dB versus 0
dB, 10 dB and 30 dB (all pairwise multiple comparison procedure, Dunn's
method, P<0.05). For an explanation of the box and whisker plots,
see Fig. 2. (D) Mean time
constants for lowering of call frequency in response to positive steps in
playback frequency. Same conventions as in C. The numbers of calls analyzed
for each condition were 401 (0 dB), 278 (10 dB), 332 (20 dB) and 175 (30 dB).
Significant differences exist for 0 dB versus 10 dB, 20 dB and 30 dB,
for 10 dB versus 0 dB and 30 dB and for 20 dB versus 0 dB
and 30 dB (all pairwise multiple comparison procedure, Dunn's method,
P<0.05).
