Abstract
Invariant target recognition by sonar requires assessment of the target strength invariably of distance despite wide variation of the echo level. Information on the echo delay and the level of the emitted pulse allows computing of the target strength. The question is: which particular mechanisms perform this computation in the biosonar of odontocetes? Investigations of the auditory evoked potentials (AEPs) during echolocation in several odontocetes have shown that comparison of the emitted pulse level, echo delay, and echo level is based on the forward masking of the echo-response by the preceding self-heard emitted click. Prolongation of the echo delay results in releasing of the echo-related AEP from masking. This release from masking compensated for the echo attenuation with distance. As a result, the echo-related AEP amplitude depended on the target strength and little depended on the target distance. Moreover, the forward-masking duration depended on the level of the emitted pulse. As a result, the echo-related AEP featured amplitude little depended on the level of the emitted pulse. The constancy of the echo-related AEP amplitude indicates the dependence of sensation level of the echo only on the target strength and the independence of both emitted click level and target distance.
Published Version
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