Auditory scene analysis by echolocation in bats

Echolocating bats transmit ultrasonic vocalizations and use information con tained in the reflected sounds to analyze the auditory scene. Auditory scen e analysis, a phenomenon that applies broadly to all hearing vertebrates, i nvolves the grouping and segregation of sounds to perceptually organize inf ormation about auditory objects. The perceptual organization of sound is in fluenced by the spectral and temporal characteristics of acoustic signals. In the case of the echolocating bat, its active control over the timing, du ration, intensity, and bandwidth of sonar transmissions directly impacts it s perception of the auditory objects that comprise the scene. Here, data ar e presented from perceptual experiments, laboratory insect capture studies, and field recordings of sonar behavior of different bat species, to illust rate principles of importance to auditory scene analysis by echolocation in bats. In the perceptual experiments, FM bats (Eptesicus fuscus) learned to discriminate between systematic and random delay sequences in echo playbac k sets. The results of these experiments demonstrate that the FM bat can as semble information about echo delay changes over time, a requirement for th e analysis of a dynamic auditory scene. Laboratory insect capture experimen ts examined the vocal production patterns of flying E. fuscus taking tether ed insects in a large room. In each trial, the bats consistently produced e cholocation signal groups with a relatively stable repetition rate (within 5%). Similar temporal patterning of sonar vocalizations was also observed i n the field recordings from E. fuscus, thus suggesting the importance of te mporal control of vocal production for perceptually guided behavior. It is hypothesized that a stable sonar signal production rate facilitates the per ceptual organization of echoes arriving from objects at different direction s and distances as the bat flies through a dynamic auditory scene. Field re cordings of E. fuscus, Noctilio albiventris, N. leporinus, Pippistrellus pi ppistrellus, and Cormura brevirostris revealed that spectral adjustments in sonar signals may also be important to permit tracking of echoes in a comp lex auditory scene. (C) 2001 Acoustical Society of America.