Mark Zagaeski
Cynthia F. Moss
Dept. of Psychol., Harvard Univ., 33 Kirland St., Cambridge, MA 02138
Echolocating bats perceive the details of their surroundings through an active bisonar system having an acuity which rivals vision in other mammals [Animal Sonar, Processes and Performance, edited by P. F. Nachtigall and P. W. B. Moore (Plenum, NY, 1988)]. To explore one facet of their acoustic imaging, big brown bats (Eptesicus fuscus) were trained to discriminate between targets based upon their surface roughness. Pairs of cylinders (7.6 cm diam by 20 cm) were covered with different grades of gravel or sandpaper. Individual bats were able to discriminate targets having a difference in mean grain size of about 0.5 mm, in general agreement with earlier results from a different bat species (Megaderma lyra). Big brown bats actively control the parameters of their short (1--5 ms) broadband (100--20 kHz) echolocation sounds to shape the acoustic information available to their bisonar systems. To monitor the bat's vocal control of echoes, vocalizations were recorded and compared to the sounds used by the same animals in a simple detection task. Echoes from the targets using synthesized bat sounds were also recorded and analyzed to explore the acoustic cues which the bats may use to perform texture discrimination. [Work supported by the Whitehall Foundation and NSF.]