The transfer function of a target limits the jitter detection threshold with signals of echolocating FM-bats

The delay jitter discrimination threshold in bats is a disputed subject. Some investigators have obtained results indicating that bats are able to discriminate alternations in delay down to 10 ns, which appears incredible for purely physical reasons. Using actual bat echolocation sequences recorded during an easy detection task to measure simulated delay jitter, it is shown here that jitter detection thresholds in the order of some tens of nanoseconds are actually physically realizable. However, if the transfer function of the target simulating apparatus is not perfect, the lowest thresholds are in the order of hundreds of nanoseconds and variable between individual bats. This phenomenon is shown to arise as a consequence of the variation in signal parameters from call to call. When the transfer function from a real jitter experiment was artificially applied to the echoes, the jitter detection thresholds again were several hundred nanoseconds. This is the first study to point out a limiting role of the transfer function of a system faced with variations in echolocation signal parameters, something that should be considered in evaluating all sonar systems with variable signal structure.