Central Control of Frequency in Biosonar Emissions of the Mustached Bat

Abstract

Doppler-compensating, echolocating bats like the mustached bat (Pteronotus p. parnellii) present excellent models for studying how sensory feedback controls subsequent motor behavior, i.e., how auditory feedback may regulate vocalization. The mustached bat emits stereotyped orientation sounds consisting of a brief rising frequency modulation (FM) followed by a long constant frequency (CF) component and ending in a short downward sweeping FM. Doppler-shifts of the echo frequency result from the difference in the bat’s velocity with respect to its surroundings. During “Doppler-shift compensation ” (DSC), these bats actively compensate for Doppler-shifts in the echo by offsetting the frequency of the orientation sound in order to stabilize the echo at the “reference frequency” (about 100–150 Hz higher than the “resting frequency” emitted when the bat detects no Doppler-shift; Schnitzler, 1968, 1970). The variability in the CF frequency emitted during DSC as observed during obstacle avoidance tests is typically ±10 to ±110 Hz (Jen and Kamada, 1982). The precision with which mustached bats control the frequency of their emitted sounds, and consequently echo frequency, is regulated directly by feedback of information from echoes. The aims of this study were to define central vocal control regions, clarify their role in the production of echolocation sounds, and investigate the role of auditory processing in the control of vocal frequency.