Abstract
The sonar of odontocetes processes echo signals within a wide range of echo levels. The level of echoes varies by tens of dB depending on the the target strength, the distance to the target, and the sound absorption by the media. The sonar of odontocetes has several mechanisms to compensate for the echo-level variation (gain control): (i) variation of emitted sonar pulse levels (the longer the distance to the target, the higher the level of the emitted pulse), (ii) short-term variation of hearing sensitivity based on forward masking of the echo by the preceding self-heard emitted pulse and subsequent release from the masking, and (iii) long-term active control of hearing sensitivity. These three mechanisms not just add to one another but act coordinately and form a united system of gain control. In particular, an increase in the sonar pulse level prolongs the distance of action of the forward-masking mechanisms. Active variation of hearing sensitivity makes the range of action of the forward-masking mechanism fitting the particular target distance and strength. These interactions of the gain-control mechanisms makes the auditory system capable of effectively analysis of echoes within a wide range of target strengths and distances.
Published Version
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