FM echolocating bats shift frequencies to avoid broadcast–echo ambiguity in clutter

Hiryu, Shizuko; Bates, Mary Ellen; Simmons, James A.; Riquimaroux, Hiroshi

doi:10.1073/pnas.1000429107

Cited by 100 publications

(94 citation statements)

References 37 publications

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“…Bats compensate for these changes by adapting the amplitude of the successive calls to prevent echo intensities from exceeding an optimal level (38)(39)(40). Additionally, echolocating bats that use frequency-modulated (FM) sonar pulses for echolocation shift their call frequencies upon receiving ambiguous echoes (41). Therefore, feed-forward loops lacking any connections to the vocal pattern-generating system would not yield the Lombard effect with its associated changes in call frequencies that we observed in DSC and intensity-compensating bats.…”

Section: Discussionmentioning

confidence: 99%

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

Hage

Jiang

Berquist

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

126

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The Lombard effect, an involuntary rise in call amplitude in response to masking ambient noise, represents one of the most efficient mechanisms to optimize signal-to-noise ratio. The Lombard effect occurs in birds and mammals, including humans, and is often associated with several other vocal changes, such as call frequency and duration. Most studies, however, have focused on noisedependent changes in call amplitude. It is therefore still largely unknown how the adaptive changes in call amplitude relate to associated vocal changes such as frequency shifts, how the underlying mechanisms are linked, and if auditory feedback from the changing vocal output is needed. Here, we examined the Lombard effect and the associated changes in call frequency in a highly vocal mammal, echolocating horseshoe bats. We analyzed how bandpassfiltered noise (BFN; bandwidth 20 kHz) affected their echolocation behavior when BFN was centered on different frequencies within their hearing range. Call amplitudes increased only when BFN was centered on the dominant frequency component of the bats' calls. In contrast, call frequencies increased for all but one BFN center frequency tested. Both amplitude and frequency rises were extremely fast and occurred in the first call uttered after noise onset, suggesting that no auditory feedback was required. The different effects that varying the BFN center frequency had on amplitude and frequency rises indicate different neural circuits and/or mechanisms underlying these changes.A ny transmission of signals between sender and receiver faces the challenge of being subjected to masking by noise. For acoustic signals, for example, animals have evolved several strategies that aid in increasing the signal-to-noise ratio, thus facilitating signal transmission. One of the most efficient mechanisms is the socalled Lombard effect, i.e., the involuntary rise in call amplitude in response to masking ambient noise (1). This effect was first described in human communication a century ago (2) and has since been found in several species of birds (3-11) and various mammals (12-17), including bats (18). In human speech, several vocal changes, such as a rise in fundamental frequency (19) or lengthening in word duration (20), are often accompanied with the Lombard effect; combined, these changes are referred to as Lombard speech (21). Vocal changes associated with the Lombard effect have rarely been analyzed in animal species. So far, noisedependent changes in call frequency have been observed in birds (8,11,22), and changes in call duration in birds and monkeys (8,12).Most animal studies, however, have focused on noise-dependent changes in call amplitude and do not examine other possible vocal changes (2-5, 7, 9, 10, 15-17). It is therefore still largely unknown how the adaptive changes in call amplitude relate to frequency shifts or call elongation and how the underlying mechanisms are linked. It is also unknown if auditory feedback from the changing vocal output is needed to drive the Lombard effect in general.Over...

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Section: Discussionmentioning

confidence: 99%

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

Hage

Jiang

Berquist

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

126

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“…They also change their pulse repetition rate -and thus their primary sensory update rate -based on environmental conditions such as the proximity of targets and clutter density. In open spaces or only moderately dense clutter, the steady-state call rate is 5-20Hz, but it rises to 40-50Hz in dense clutter (Hiryu et al, 2010;Moss and Surlykke, 2010;Petrites et al, 2009;Saillant et al, 2007). These bats receive essentially stroboscopic updates of the world around them (Surlykke and Moss, 2000).…”

Section: Introductionmentioning

confidence: 99%

Spatial memory and stereotypy of flight paths by big brown bats in cluttered surroundings

Barchi

Knowles

Simmons

2013

Journal of Experimental Biology

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SUMMARYThe big brown bat, Eptesicus fuscus, uses echolocation for foraging and orientation. The limited operating range of biosonar implies that bats must rely upon spatial memory in familiar spaces with dimensions larger than a few meters. Prior experiments with bats flying in obstacle arrays have revealed differences in flight and acoustic emission patterns depending on the density and spatial extent of the obstacles. Using the same method, combined with acoustic microphone array tracking, we flew big brown bats in an obstacle array that varied in density and distribution in different locations in the flight room. In the initial experiment, six bats learned individually stereotyped flight patterns as they became familiar with the space. After the first day, the repetition rate of sonar broadcasts dropped to a stable level, consistent with low-density clutter. In a second experiment, after acquiring their stable paths, each bat was released from each of two unfamiliar locations in the room. Each bat still followed the same flight path it learned originally. In a third experiment, performed 1month after the first two experiments, three of the bats were re-flown in the same configuration of obstacles; these three resumed flying in their accustomed path. The other three bats were flown in a mirror-image reconfiguration of the obstacles; these bats quickly found stable flight paths that differed from their originally learned paths. Overall, the flight patterns indicate that the bats perceive the cluttered space as a single scene through which they develop globally organized flight paths.

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“…This interpulse interval is long enough to accommodate echoes from targets located as far as 5 m from each other, without any interference from echoes from the next emission. Avoiding overlaps between the streams of echoes generated from successive emissions seems to be important for bats, as they shift the frequency content of their calls if echoes from the first emission are still arriving at the time when a second call is produced 32 .…”

Section: Discussionmentioning

confidence: 99%

Blurry topography for precise target-distance computations in the auditory cortex of echolocating bats

et al. 2013

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Echolocating bats use the time from biosonar pulse emission to the arrival of echo (defined as echo delay) to calculate the space depth of targets. In the dorsal auditory cortex of several species, neurons that encode increasing echo delays are organized rostrocaudally in a topographic arrangement defined as chronotopy. Precise chronotopy could be important for precise target-distance computations. Here we show that in the cortex of three echolocating bat species (Pteronotus quadridens, Pteronotus parnellii and Carollia perspicillata), chronotopy is not precise but blurry. In all three species, neurons throughout the chronotopic map are driven by short echo delays that indicate the presence of close targets and the robustness of map organization depends on the parameter of the receptive field used to characterize neuronal tuning. The timing of cortical responses (latency and duration) provides a binding code that could be important for assembling acoustic scenes using echo delay information from objects with different space depths.

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FM echolocating bats shift frequencies to avoid broadcast–echo ambiguity in clutter

Cited by 100 publications

References 37 publications

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

Spatial memory and stereotypy of flight paths by big brown bats in cluttered surroundings

Blurry topography for precise target-distance computations in the auditory cortex of echolocating bats

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