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First published online May 19, 2008
Journal of Experimental Biology 211, 1714-1718 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013862
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A false killer whale adjusts its hearing when it echolocates

Paul E. Nachtigall1,* and Alexander Y. Supin2

1 Marine Mammal Research Program, Hawaii Institute of Marine Biology, University of Hawaii, PO Box 1106, Kailua, HI 96734, USA
2 Institute of Ecology and Evolution of the Russian Academy of Sciences, 33 Leninsky Prospekt, 119071 Moscow, Russia


Figure 1
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  		Fig. 1. Relative positions of the animal and equipment during experiments and block diagram of data acquisition during echolocation trials. T, target; H, hydrophone; S, hoop station; E, electrodes; EEGamp, EEG amplifier; A/D+Aver, analog-to-digital converter and averager; Store, data storage; Sound-amp+Trig, sound amplifier and trigger; and Scope, monitoring oscilloscope. Distance from target to the animal's ears (*), 2.0 m; distance to the expected sound-production region, 1.9 m; distance to the triggering hydrophone, 1 m.

 

Figure 2
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  		Fig. 2. Thresholds for passive false killer whale-like clicks presented 2 m in front of the whale (specified in sound-pressure level, SPL) and thresholds for clicks produced by the whale (specified in source level). Note that (with targets present) the whale is about 40 dB less sensitive to clicks that it produces as compared with passively presented clicks. ABR, auditory brainstem response.

 

Figure 3
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  		Fig. 3. Averaged auditory evoked potential (AEP) records. Echolocation-related evoked potential records at target distances of 1, 1.5, 2, 3, 5 and 8 m. The initial bold arrow marks the outgoing pulse-related ABR while other arrows indicate the echo-related ABRs. The active electrode negativity is upward.

 

Figure 4
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  		Fig. 4. Echolocation-related AEPs recorded at different target strengths (–40 to –22 dB, as designated in panels A–D) and different target distances (1.5, 3 and 6 m) as indicated on the records in each panel. The arrows indicate the AEP complex as echo related.

 

Figure 5
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  		Fig. 5. The AEP related to the outgoing signal is dependent on the target strength (the argument) and distance (the parameter).

 




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