Echolocating bats dynamically regulate hearing sensitivity: Behavioral and physiological evidence

Abstract

James Simmons's previous study on automatic gain control in the big brown bat has suggested the contractions of middle-ear muscle and forward masking impairing hearing sensitivity during vocalization. The influence of vocal production can be extremely severe for bat species that produce constant-frequency (CF) sonar signals. However, perceptual hearing sensitivity and the underlying mechanisms in CF bats remain virtually unexplored. In this work, combing a 2-AFC psychophysical setup and an electrophysiological setup, we measured the hearing sensitivity of a CF bat, Hipposideros pratti, either in a passive listening (PL) task to detect pure tones, an active listening (AL) task to detect pure tones triggered by its vocalization, or a phantom Echo task. Behavioral data show that H. pratti had the best hearing sensitivity of approximately 0 dB SPL in the PL task, but nearly 40 dB worse in the Echo task. In the AL task, all bats gradually increased call frequency by 0.8 to 1.1 kHz to overcome self-generated auditory masking. Preliminary neurophysiological data indicate that the neural responses in the midbrain inferior colliculus can be highly plastic. Together, our data suggest that echolocating bats dynamically control the hearing sensitivity during vocalization in a complex manner.