Figure - available from: Journal of Comparative Physiology A
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Temporal and spectral properties of echolocation calls used by the bats for detecting echo amplitude modulations. a Effect of modulation depth (= task difficulty). The distribution of inter-call intervals (Row 1), call durations (Row 2) and spectral centroids (Row 3) did not change as a function of modulation depth in any of the four bats (columns). b Effect of modulation rate at threshold modulation depth. Data show the extent to which the presented modulation rate lead the animals to adjust ensonification parameters. Again, the distribution of inter-call intervals (Row 1), call durations (Row 2) and spectral centroids (Row 3) did not change systematically as a function of presented modulation rate in the four bats. Residual changes in spectral-centroid distributions result from a change of recording device during data acquisition and do not reflect a change in the bats’ ensonification strategy. All data are shown as normalized bin counts with color-coded probability
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Bats use echolocation to detect targets such as insect prey. The echolocation call of frequency-modulating bats (FM bats) typically sweeps through a broad range of frequencies within a few milliseconds. The large bandwidth grants the bat high spatial acuity in depicting the target. However, the extremely short call duration and the overall low duty...
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Acoustic deterrents have shown potential as a viable mitigation measure to reduce human impacts on bats, however, the mechanisms underpinning acoustic deterrence of bats have yet to be explored. Bats avoid ambient ultrasound in their environment and alter their echolocation calls in response to masking noise. Using stereo thermal videogrammetry and...
Citations
Animals need to acquire adequate and sufficient information to guide movements, yet information acquisition and processing is costly. Animals thus face a trade-off between gathering too little and too much information and, accordingly, actively adapt sensory input through motor control. Echolocating animals provide the unique opportunity to study the dynamics of adaptive sensing in naturally behaving animals, since every change in the outgoing echolocation signal directly affects information acquisition and the perception of the dynamic acoustic scene. Here we investigated the flexibility with which bats dynamically adapt information acquisition depending on a task. We recorded the echolocation signals of wild-caught Western barbastelle bats ( Barbastella barbastellus ) while flying through an opening, drinking on the wing, landing on a wall, and capturing prey. We show that the echolocation signal sequences during target approach differed in a task-dependent manner; bats started target approach earlier and increased information update rate more when the task became increasingly difficult, and bats also adjusted dynamics of call duration shortening and peak frequency shifts accordingly. These task-specific differences existed from the onset of object approach, implying that bats plan their sensory-motor program for object approach exclusively based on information received from search call echoes. We provide insights into how echolocating animals deal with the constraints they face when sequentially sampling the world through sound by adjusting acoustic information flow from slow to extremely fast in a highly dynamic manner. Our results further highlight the paramount importance of high behavioural flexibility for acquiring information.
Many echolocating bats forage close to vegetation - a chaotic arrangement of prey and foliage where multiple targets are positioned behind one another. Bats excel at determining distance: they measure the delay between outgoing call and returning echo. In their auditory cortex, delay-sensitive neurons form a topographic map, suggesting that bats can resolve echoes of multiple targets along the distance axis - a skill crucial for the forage-amongst-foliage scenario. We tested this hypothesis combining an auditory virtual reality with formal psychophysics: We simulated a prey item embedded in two foliage elements, one in front of and one behind the prey. The simulated spacing between “prey” (target) and “foliage” (maskers) was defined by the inter-masker delay (IMD). We trained Phyllostomus discolor bats to detect the target in the presence of the maskers, systematically varying both loudness and spacing of the maskers. We show that target detection is impaired when maskers are closely spaced (IMD<1 ms), but remarkably improves when the spacing is increased: the release from masking is about 5 dB for intermediate IMDs (1-3 ms) and increases to over 15 dB for large IMDs (≥ 9 ms). These results are well comparable to earlier work on bats’ clutter interference zone (Simmons et al., 1988). They suggest that prey would enjoy considerable acoustic protection from closely spaced foliage, but also that the range resolution of bats would let them “peek into gaps”. Our study puts target ranging into a meaningful context and highlights the limitations of computational topographic maps.
Echo-imaging evolved as the main remote sense under lightless conditions. It is most precise in the third dimension (depth) rather than in the visually dominating dimensions of azimuth and elevation. We asked how the auditory system accesses spatial information in the dimensions of azimuth and elevation with a sensory apparatus that is fundamentally different from vision. We quantified echo-acoustic parameters of surface-wave patterns with impulse-response recordings and quantified bats' perceptual sensitivity to such patterns with formal psychophysics. We demonstrate that the spectro-temporal auditory representation of a wave pattern implicitly encodes its spatial frequency. We further show that bats are much more sensitive to wave patterns of high spatial frequencies than of low spatial frequencies. We conclude that echo-imaging accesses spatial information by exploiting an inherent environmental high-pass filter for spatial frequency. The functional similarities yet mechanistic differences between visual and auditory system signify convergent evolution of spatial-information processing. : Acoustics; Bioacoustics; Biological Sciences; Zoology Subject Areas: Acoustics, Bioacoustics, Biological Sciences, Zoology
