Abstract
Acute auditory processing in bats is typically associated with echolocation. A subset of bats, called gleaners, listens to prey-generated noise to hunt surface-dwelling prey. Gleaners depend less on echolocation to hunt and, therefore, accurate localization of prey-generated noise is necessary for foraging success. Here we studied azimuth sound localization behavior in the pallid bat, a gleaning bat in which spatial encoding has been studied extensively. We tested pallid bats on a relatively difficult open loop task (single sound, duration ≤ 200 ms). The bats were trained to face the midline when stimulus was presented, and this was confirmed with video analysis. Bats localized broadband noise (5–30 kHz) from 1 out of 11 speakers spaced evenly across the horizontal plane of the frontal sound field. Approach to the correct speaker was rewarded. Pallid bats show accurate localization near the midline with mean errors between 3–6°. Remarkably, the accuracy does not decline significantly at peripheral locations with bats averaging <~7° error upto 72° off midline. Manipulation of stimulus bandwidth shows that higher frequencies (20–30 kHz) are necessary for accurate localization. Comparative studies of gleaning bats will reveal convergent adaptations across auditory systems for non-echolocation-based behaviors in bats.
Highlights
Sound localization is a primary function of the auditory system
The notion that azimuth function slopes are where neurons provide maximal information for spatial discrimination leads to the prediction that the bat should perform relatively accurately at peripheral locations
Bats were trained to face the midline for sound presentation
Summary
Sound localization is a primary function of the auditory system. The ability to localize sounds is important for successful foraging, avoiding predation, and locating a mate. Given the dependence of gleaning bats on localizing relatively low intensity, prey-generated noise in the dark, it is likely that they have specializations for sound localization. A third of this noise-selective region contains neurons with peaked azimuth selectivity functions with preferred azimuth at ~0–15° This suggests the presence of a cortical region specialized for midline azimuth localization. Ear directionality of the pallid bat is broad for frequencies below 15 kHz, and begins to sharpen and generate increasing IIDs for frequencies above 15 kHz18 These studies make several predictions regarding azimuth localization by the pallid bat. The notion that azimuth function slopes are where neurons provide maximal information for spatial discrimination leads to the prediction that the bat should perform relatively accurately at peripheral locations. Ear directionality and IID/azimuth correlation results indicate that azimuth localization accuracy should improve with inclusion of frequencies >15 kHz14,16,18
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