ECHO SPL, TRAINING EXPERIENCE, AND EXPERIMENTAL PROCEDURE INFLUENCE THE RANGING PERFORMANCE IN THE BIG BROWN BAT, EPTESICUS-FUSCUS

Four Eptesicus fuscus were trained in a range discrimination experimen t to choose the closer of two phantom targets. Echo attenuation was ro ving between trials returning echoes ranging from -10 dB to -50 dB SPL (sound pressure level) relative to emission SPL. Discrimination thres holds were determined. After sufficient training, ranging performance was stable and about the same in the range between -20 dB and -50 dB w ith range difference thresholds around 300 mu s. At -10 dB, performanc e was poor even after long training. After additional training at a co nstant relative echo SPL of -30 dB and a delay difference of 300 mu s the performance measured with roving echo SPL improved at all relative echo SPL between -20 dB and -50 dB but not at -10 dB. The new experim ental procedure improved the performance by additional learning, and t he bats generalized over a wide range of relative echo SPL. Threshold improved to 100 mu s when measured at a constant relative echo SPL of -30 dB, again indicating the influence of the experimental procedure. In correspondence to neurophysiological data the ranging performance d eteriorates if the echo SPL is close to the emission SPL. Signal durat ion and emission SPL were variable during range discrimination.