Gain variation in the odontocete biosonar when prior information about echo parameters is or is not available

Abstract

In a false killer whale Pseudorca crassidens, sonar clicks and auditory evoked potentials (AEP) were recorded during echolocation with simulated echo. In one experimental series, echo delay and transfer factor varied randomly from trial to trial (random presentation). With this manner of variation of echo parameters, the animal never could anticipated the parameter values. In another series, a combination of the echo delay and transfer factor was kept constant during several dozens of trials; therefore, the information about echo parameters was potentially available for the animal (ordered presentation). Mean click level decreased with shortening the delay and increasing the transfer factor, more at the ordered presentation rather than at random presentation. AEPs to the self-heard emitted clicks decreased with shortening the delay and increasing the echo level, equally at both random and ordered presentations. AEPs to echo increased with increasing the echo level, little dependent on echo delay at random presentation but much more dependent on delay at ordered presentation. So adjustment of the whale's biosonar to the echo parameters was possible without prior information about the echo parameters; however availability of the prior information provided additional capabilities for adjustment of both the transmitting and receiving parts of the biosonar.