Sonar detection of jittering real targets in a free-flying bat.

The auditory system measures time with exceptional precision. Echolocating bats evaluate the time delay between call and echo to measure object range. An extreme and disputed result on ranging acuity was found in the virtual delay jitter experiments. In these studies, echoes with alternating delays were played back to bats, which detected a jitter down to 10 ns, corresponding to a ranging acuity of 1.7 microm. The current study was designed to measure the ranging acuity of the nectarivorous bat Glossophaga soricina under semi-natural conditions. Three free-flying bats were trained to discriminate between a stationary loudspeaker membrane and a membrane sinusoidally vibrating at 10 Hz. At detection threshold, the average peak-to-peak displacement of the vibrating membrane was 13 mm, corresponding to an echo delay jitter of 75 micros. The perceived jitter from call to call, which depends on the pulse interval and the call emission time relative to the membrane phase, was simulated for comparison with the virtual jitter experiments. This call-to-call jitter was between 20 to 25 micros (ca. 4 mm ranging acuity). These thresholds between 20 and 75 micros (4-13 mm) fall within both ecologically and physiologically plausible ranges, allowing for sufficiently precise navigation and foraging.