Discrimination performance and echolocation signal integration requirements for target detection and distance determination in the CF/FM bat,Noctilio albiventris

Summary Bats of the speciesNoctilio albiventris were trained to detect the presence of a target or to discriminate differences in target distance by means of echolocation. During the discrimination trials, the bats emitted pairs of pulses at a rate of 7–10/s. The first was an 8 ms constant frequency (CF) signal at about 75 kHz. This was followed after about 28 ms by a short-constant frequency/ frequency modulated (short-CF/FM) signal composed of a 6 ms CF component at about 75 kHz terminating in a 2 ms FM component sweeping downward to about 57 kHz. There was no apparent difference in the pulse structure or emission pattern used for any of the tasks. The orientation sounds of bats flying in the laboratory and hunting prey under natural conditions follow the same general pattern but differ in interesting ways.The bats were able to discriminate a difference in target distance of 13 mm between two simultaneously presented targets and of 30 mm between single sequentially presented targets around an absolute distance of 35 cm, using a criterion of 75% correct responses.The bats were unable to detect the presence of the target or to discriminate distance in the presence of continuous white noise of 54 dB or higher SPL. Under conditions of continuous white noise, the bats increased their pulse repetition rate and the relative proportion of CF/FM pulses.The bats required a minimum of 1–2 successive CF/FM pulse-echo pairs for target detection and 2–3 to discriminate a 5 cm difference in distance. When the distance discrimination tasks were made more difficult by reducing the difference in distance between the two targets the bats needed to integrate information from a greater number of successive CF/FM pulse-echo pairs to make the discrimination.Abbreviations CF constant frequency - FM frequency modulation