A neural mechanism for detecting target distance independently of target velocity in echolocation of bat

Most species of bats making echolocation use frequency modulated (FM) ultrasonic pulses to measure the distance to targets such as flying insects. These bats detect with a high accuracy the arrival time differences between emitted pulses and their echos generated by targets, even though the targets are moving. We propose a neural mechanism by which the bat may detect the time differences independently of the target velocity using FM ultrasonic pulses. The neural processing model presented consists of the networks for calculating the temporal correlation between pulse and echo for each frequency and network for integrating the calculated results over the frequency range used by the bat. We found that the key factor generating the detection independent of target velocity is the value of frequency modulation rate