Echolocation Sounds Research Articles

Discrimination of stationary and revolving targets by the FM bat, Eptesicus fuscus

Four FM bats, Eptesicus fuscus, were trained to use their echolocation ability to discriminate a revolving target and a stationary target that were randomly and simultaneously placed in the directions of two of a three-ramp platform. The bat-to-target distance ranged from 30 to 100 cm. The target was of semicircular shape with a radius of 16 mm and was made of thin copper plate of 0.05 mm. During the test, the frequency of a bat's approach to either target was recorded at each bat-to-target distance. Such a study revealed that a bat approached a revolving target more often than a stationary one. During the test, echolocation sounds emitted by three bats were recorded at bat-to-target distances of 40 and 80 cm. Analysis of these sounds revealed that there was no obvious difference in signal duration, interpulse intervals, or frequency contents among these sounds. A partial lesion was made electrolytically in the right hemisphere of the cerebellum of one bat. However, our study showed that such a partial lesion did not affect the bat's discrimination ability or the signal parameters of its emitted sounds. [Work supported by NSF 80-07348 and USPH 1-K04-NS00433 to Philip H.-S. Jen.]

Discrimination of surface-structured targets by the echolocating batMyotis myotis during flight

1. Myotis myotis was trained to discriminate a plate with 8 mm deep holes from plates of stepwise varied hole depth. Depth differences in the two plates equal or larger than 1 mm were discriminated by the echolocating bat (Fig. 3). 2. In a second series of experiments a plate with 4 mm deep holes was discriminated from other plates with hole depth differences equal or larger than 0.8 mm (Fig. 3). 3. Echolocation sounds emitted during discrimination are of the same type as those used for catching prey in air or on the ground (Fig. 2). With increasing difficulty of the discrimination task the flight speed of the bat was reduced (Fig. 1). 4. An incidental experiment disclosed the ability to discriminate surface structures with the resolution of roughness produced by 30 μm protrusions in the surface (Fig. 4). 5. We conclude thatMyotis myotis discriminated hole depth differences by spectral, and not by time, cues in the echoes.

Adaptive echolocation sounds in the batRhinopoma hardwickei

1. Rhinopoma hardwickei were studied under natural conditions in the Madurai region of southern India. 2. Frequency modulated (FM) sounds of 3 ms duration were emitted shortly before landing and during times when 10–70 individuals were flying in clusters as they left their roosts. 3. Constant frequency (CF) sounds of 48 ms duration were produced in open space by single flying bats and by bats flying in a group. At these times the most intense component was the second harmonic. 4. When bats flew in a group the frequencies of the CF-sounds emitted by different individuals were in three different bands (30.0, 32.5, and 35.0 kHz) whereas single flying bats used only 32.5 kHz. Evidence is presented that shows thatRhinopoma hardwickei flying in groups regulate the frequency of their individual CF-components and in this way they avoid jamming one another. 5. After landing a pure tone multi-harmonic sound of long duration (maximally 100ms) is emitted. In this sound the fundamental frequency is dominant. Its significance, either communicative and/or echolocative, is not clear. 6. The possible role of different types of sounds recorded in different orientation situations is discussed.

Ears adapted for the detection of motion, or how echolocating bats have exploited the capacities of the mammalian auditory system

Bats use the rich food resources of the night by specializing in audition. They emit short echolocation sounds and listen to the echoes returning from potential prey. The bat’s auditory system analyzes spectral and temporal parameters of echoes for detecting, locating, and identifying a target. Different bat species have solved the problem of acoustic target detection and pattern recognition even in clustered situations by focusing on certain acoustical features of a target. The specialized motion detection by horseshoe bats, for instance, analyzes small echofrequency shifts modulated onto a long constant frequency echolocation signal. These frequency modulations are Doppler shifts within echoes returning from wing beating insects. For detecting modulations as small as 10 Hz or 0.01%, horseshoe bats have in the cochlea an extremely narrow filter (Q?500) matched to the carrier frequency (i.e., echolocation sound) of 83 kHz. The filter is realized by structural differentiations of the basilar membrane and the filter frequencies are represented on the basilar membrane in an expanded fashion. We have called this specialized patch of the basilar membrane an ’’acoustical fovea.’’ The ’’foveal frequencies’’ are largely overrepresented in the tonopical arrangement of the ascending auditory pathway. The bats have developed a feedback system which lowers the emitted frequency during flight in such a way that the Doppler shifted echofrequency is kept precisely at a fixed reference frequency of the fovea. This feedback system and other neuronal data disclose an intricate coupling of the auditory and vocalizing system. The evolution of echolocation in bats has driven the analyzing capacities of audition in both frequency and time domain close to theoretical limits. Investigations of such specialized systems give fascinating insights into capacities and possible general principles of auditory information processing.

Ears adapted to detect motion, or how echolocating bats exploit the capacities of the mammalian auditory system

Bats avail themselves of the rich food resources of the night by specializing in audition. They emit short echolocation sounds and listen to the echoes returning from potential prey and the environment. The bat's auditory system analyzes spectral and temporal parameters of echoes for detecting, precisely locating, and identifying a target. Different bat species have solved the problem of acoustic target detection and pattern recognition even in heavily clustered situations by focusing on certain acoustical features of the targets. The specialized motion defection by Horseshoe bats, for instance, analyzes small echofrequency shifts modulated onto a long constant frequency echolocation signal. These frequency modulations are Doppler shifts of echoes returning from wing beating insects. For detecting modulations as small as 10 Hz or 0.01%, Horseshoe bats have in the cochlea an extremely narrow filter (Q = ca. 500) matched to the carrier frequency (i.e., echolocation sound) of 83 kHz. The filter is based on mechanical principles and realized by structural differentiations of the basilar membrane. We have called this specialized patch of the basilar membrane an “acoustical fovea.” In analogy to the visual fovea the “foveal frequencies” are largely over‐represented in the tonopical arrangement of the ascending auditory pathway. The bats have developed a feedback system which lowers the emitted echolocation frequency in such a way that the Doppler shifted echofrequency is kept precisely at a fixed reference frequency close to 83 kHz. This feedback system and additional neuronal data disclose an intricate coupling of the auditory and vocalizing system. The evolution of echolocation in bats has driven the analyzing capacities of audition close to theoretical limits. Investigations in such specialized systems give fascinating insights into possible general principles of auditory information processing.

Evidence for separate echolocation and communication processing areas in the inferior colliculus of bats

Although acoustic signals are used by bats for both echolocation and for communication little is known about how communication signals are represented in the bat's brain. Recently we have obtained data which strongly suggest that the inferior colliculus of Mexican free-tailed bats (Tadarida brasiliensis mexicana) is functionally partitioned into two major subdivisions: a medial region having neurons specialized for processing echolocation signals and a lateral region having neurons that appear to be well suited for analyzing communication sounds. The features which distinguish the two regions are marked differences in tonotopic organization as well as in tuning and discharge properties. The tonotopic organization of the medial region is mammalian in design. The characteristic frequencies (CF) of neurons in this region increase in an orderly manner with depth and encompass the full compliment of frequencies in the echolocation sounds emitted by this species. The neurons in the medial region are very sensitive to brief frequency-modulated (FM) signals which mimic the natural orientation cries and exhibit fast recovery. In striking contrast, the tonotopy of the lateral portion of the colliculus is characterized by a relative constancy of CFs with depth. The CFs of neurons situated dorsally are 20-22 kHz and only increase to 24-26 kHz in the deepest parts of the lateral region. In addition, the majority of neurons are either unresponsive to brief FM signals or have very high thresholds for responding to these stimuli. A final feature is that many neurons have two frequencies of maximal sensitivity in their tuning curves. Such multiply tuned neurons were only found in the lateral region. Many of the communication sounds emitted by Mexican free-tailed bats have long constant frequency portions. The fundamental frequencies range from about 20-25 kHz and are rich in harmonics, features which correlate closely with the tuning features of neurons in the lateral region. [Supported by NIH Grants NS13276 and NS00367.]

The development of flight, foraging, and echolocation in the little brown bat (Myotis lucifugus)

1. Two colonies of little brown bats,Myotis lucifugus (Vespertilionidae), were studied for two summers. The young could not perform practice flights within the buildings where they roosted. Young of estimated relative ages and adults were light-tagged, released, and tracked to determine the development of flying skills and foraging behavior. Orientation sounds were observed and tape-recorded. 2. The earliest flights at ca. 19–20 days of age were usually relatively brief (a few tens of seconds or less) but still remarkable considering the absence of practice. The young at first emerged after adults had left to forage, avoided entering acoustically complex habitats, flew slowly within about 50 m of the roost, and made frequent, awkward landings. They avoided other flying bats and did not pursue insects. More time was spent in rest than flight. 3. Slightly older young, beginning at ca. 22–23 days, gradually increased their flight distance and duration (Table 1) and began to hunt insects in clearings or at the forest edge. Some adopted a ‘flycatcher’ hunting style at this time. They still avoided flying conspecifics. 4. The final phase of development began at about days 24–27 and may last 2 weeks or more. It involved virtually continual flight, insect pursuits, and maneuvers that became indistinguishable from those of adults, and also gradual integration with the adults during emergence, flight along traditional routes, and foraging. 5. The echolocation sounds of young of known and estimated relative ages were recorded in the field, a flight cage, or large room. Again, development was rapid. Landing buzzes always occurred, even in the first flight, although the progressive changes in frequency were sometimes not as uniform as in adults. 6. The pulses during all phases of early flight were of lower frequency than in adults. Those emitted during cruise and approach phases were frequently paired. There is possible ontogenetic and phylogenetic significance to this pairing. Within a few days, the pairing disappeared and within ca. 1 week all echolocation parameters became similar to those of adults (Fig. 1; Table 2).

Prey catching with and without echolocation in the Indian false vampire (Megaderma lyra)

1. Under laboratory conditions echolocation sounds were recorded from four Megaderma lyra catching a mouse in complete darkness from an experimental table. Flight paths and sequences of sound emission were synchronously recorded by stroboscopic photography and high-speed tape-recording (Figs. 1 and 2). 2. During approach toward a live mouse in 54% of 35 completely recorded flights, the bat emitted ultrasounds, but only up to five sounds could be recorded during a complete approach (Fig. 1a). During the other 46% of the 35 flights, the bat did not emit a sound, yet successfully caught the prey (Fig. 1 b). 3. When a dead mouse was offered, only one bat successfully echolocated the dead mouse and emitted a specific double sound sequence of intense ultrasounds. The other three bats did not take off for an approach. When mouse noises were substituted for the live mouse, the approach flight of two of the bats was immediately triggered as if a live mouse were offered. Only a few echolocation sounds were emitted in both cases. 4. It is concluded that M. lyra can locate the noise of live prey in complete darkness, without the use of echolocation.

Vocalization influences auditory processing in collicular neurons of the CF-FM-bat,Rhinolophus ferrumequinum

1. In awake Greater Horseshoe bats (Rhinolophus ferrumequinum) the responses of 64 inferior colliculus neurons to electrically elicited vocalizations (VOC) and combinations of these with simulated echoes (AS: pure tones and AS(FM): sinusoidally frequency-modulated tones mimicking echoes from wing beating insects) were recorded. 2. The neurons responding to the species-specific echolocation sound elicited by electrical stimulation of the central grey matter had best frequencies between 76 and 86 kHz. The response patterns to the invariable echolocation sound varied from unit to unit (Fig. 1). 3. In 26 neurons the responses to vocalized echolocation sounds markedly differed from those to identical artificial ones copying the CF-portion of the vocalized sound (AS). These neurons reacted with a different response to the same pure tone whether it was presented artificially or vocalized by the bat (Fig. 2). In these neurons vocalization activities qualitatively alter the responsiveness to the stimulus parameters of the echoes. 4. A few neurons neither responded to vocalization nor to an identical pure tone but discharged when vocalization and pure tone were presented simultaneously. 5. In 2 neurons synchronized encoding of small frequency-modulations of the pure tone (mimicking an echo returning from a wing beating prey) occurred only during vocalization. Without vocalization the neurons did not respond to the identical stimulus set (Fig. 3). In these neurons vocalization activities enhanced FM-encoding capabilities otherwise not present in these neurons. 6. FM-encoding depended on the timing between vocalization and frequency-modulated signal (echo). As soon as vocalization and FM-signal no more overlapped or at least 60–80 ms after onset of vocalization synchronized firing to the FM was lost (4 neurons) (Fig. 4). 7. 4 neurons weakly responded to playbacks of the bat's own vocalization 1 ms after onset of vocalization. But when the playback frequency was shifted to higher frequencies by more than 400 Hz the neurons changed firing patterns and the latency of the first response peak (Fig. 5). These neurons sensitive to frequency shifts in the echoes returning during vocalization may be relevant to the Doppler-shift compensation mechanism in Greater Horseshoe bats.

Echolocation and obstacle avoidance in the hipposiderid batAsellia tridens

The echolocation sounds of the hipposiderid batAsellia tridens consist of a constant frequency (cf) component followed by a frequency modulated (fm) terminal downward sweep of 19–21 kHz. The cf-part constitutes about 7/10 of the entire signal. In individual roosting animals the frequencies of the cf-part of consecutive sounds (resting frequency) is kept very constant but varies from bat to bat. In 18Asellia tridens resting frequencies between 111–124 kHz have been measured.

Echolocation performance of the vampire bat (Desmodus rotundus).

The neotropical vampire bats (Desmodus rotundus) echolocate using ultrasonic pulses like those of the Latin American phyllostomatid bats. In this paper the orally produced echolocation sounds of Desmodus are analysed and the performance of the echolocation system is studied in two-choice training experiments on two vampire bats. Ability to detect objects is relatively limited; both animals were capable of discerning the presence of a 1 cm wide metal strip at a distance of 50 cm, but they failed with 0.5 cm wide strips. The ultrasonic pulses produced at a distance of 50 cm appear to sample an area with a diameter of 2.5 to 3.0 cm (i.e., the solid angle tested with each pulse is 3 degrees to 3 degrees 40' in extent).

Storage of Doppler-shift information in the echolocation system of the ?CF-FM?-bat,Rhinolophus ferrumequinum

The greater horseshoe bat (Rhinolophus ferrumequinum) emits echolocation sounds consisting of a long constant-frequency (CF) component preceeded and followed by a short frequency-modulated (FM) component. When an echo returns with an upward Doppler-shift, the bat compensates for the frequency-shift by lowering the emitted frequency in the subsequent orientation sounds and stabilizes the echo image. The bat can accurately store frequency-shift information during silent periods of at least several minutes. The stored frequency-shift information is not affected by tone bursts delivered during silent periods without an overlap with an emitted orientation sound. The system for storage of Doppler-shift information has properties similar to a sample and hold circuit with sampling at vocalization time and with a rather flat slewing rate for the stored frequency information.

Dynamic properties of the compensation system for doppler shifts in the bat,Rhinolophus ferrumequinum

1. Echolocation sounds of the batRhinolophus ferrumequinum were played back to the bat as artificial echoes shifted in frequency by a few kHz (0–4 kHz) without distortion of the amplitude and frequency pattern of the sound. The simulated Doppler shifts in the echoes were modulated either sinusoidally or in step functions. 2. The bats did not compensate for frequency shifts within one sound, but in the sounds subsequent to the introduction of the shift. 3. Responses to symmetrical sinusoidal modulations of the echo from −2 kHz to +2kHz demonstrate that in the dynamic situation the bat compensates for positive frequency shifts and ignores negative frequency shifts (Fig. 2). Asymmetrical sinusoidal modulations between 0 Hz and different positive frequency shifts (1, 2, 3, and 4 kHz) yielded amplitude and phase response curves for modulation frequencies between 0.01 and 2 Hz (Fig. 5, 6). The response to step functions gave the time course for positive and negative changes of the frequency shift (Fig. 7). 4. The Doppler compensation system shows nonlinearities: The response of the system depends on the sign of the frequency shift change. Positive changes of the frequency shift in sinusoidal modulations are optimally followed by the system, when it is considered as a sampling system, in which the pulse repetition rate is the sampling rate. The response to negative frequency shift changes is much slower (Fig. 6). With an increase of the modulation frequency the response is DC-shifted. The amplitude and phase response curves depend on the amplitude of the frequency shifts presented in the modulation (Table 1, 2). 5. The maximum compensation between two succeeding bat orientation sounds was 1400 Hz, giving a frequency change of about 10 Hz/msec. This value is about the same as the minimum frequency modulation of the constant frequency portion of the sound detected by the bat. 6. The dynamic properties of the Doppler shift compensation system are discussed in the context to neurophysiological findings on the hearing system of the bat.

Bandwidth limitations and analysis of cetacean sounds, with comments on "Delphinid sonar: measurement and analysis".

Historically, recording of cetacean sounds has encompassed an ever-enlarging bandwidth as equipment has improved and repertories of sounds from each species have become better known. The effect of equipment bandwidth limitations on our knowledge of these sounds is discussed. Very short sounds whose components are above the bandwidth of the equipment nevertheless are recorded as low-level broad-band pulses. The distortions of transient pulses reported by Diercks, Trochta, and Evans [“Delphinid sonar: measurement and analysis,” J. Acoust. Soc. Am. 54, 200 (1973)] are suggestive of overload resonance and nonlinearity. The evidence does not seem to support the implication that these animals produce similar echolocation sounds in spite of different situations and tasks, or that lower-frequency emphases in their pulsed sounds are artifacts of limited bandwidth equipment.

The resolution of target range by echolocating bats.

Using simultaneous discrimination procedures the acuity of resolution of differences in target range has been determined on four species of echolocating bats (Eptesicus fuscus, Phyllostomus hastatus, Pteronotus suapurensis, and Rhinolophus ferrumequinum). All can discriminate range differences as small as 1 to 3 cm and, for the first three species, the acuity of range resolution appears to be independent of absolute range, at least at short distances. In Eptesicus range discrimination mediated in terms of the arrival times of echoes returning from different targets. Comparisons between discrimination performance and autocorrelation functions of echolocation sounds used in the discriminations suggest that these bats possess some neural equivalent of a matched-filter, ideal sonar receiver which functionally cross-correlates a replica of the outgoing signal with the returning echo to detect the echo and determine its arrival time. Eptesicus and Phyllostomus both use the entire FM signal for target ranging. Pteronotus uses its entire compound, short-duration CF/FM signal for ranging, while Rhinolophus separates the FM component from its compound, long-duration CF/FM sound and uses the FM part for target ranging. The results indicate different functions for the CF and FM components of bat sonar cries, and they suggest that the matched-filter or cross-correlation approach to echolocation is appropriate.

Collicular responses to the frequency modulated final part of echolocation sounds in Rhinolophus ferrum equinum

Collicular evoked potentials in Rhinolophus ferrum equinum show very prominent responses to the final frequency modulated part of a acoustic stimulus, simulating the natural echolocation sound.

Patterns of acoustically evoked discharges of neurons in the mesencephalon of the bullfrog.

ArticlesPATTERNS OF ACOUSTICALLY EVOKED DISCHARGES OF NEURONS IN THE MESENCEPHALON OF THE BULLFROGH. David PotterH. David PotterPublished Online:01 Nov 1965https://doi.org/10.1152/jn.1965.28.6.1155MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByEffect of sound pressure level on contralateral inhibition underlying duration-tuned neurons in the mammalian inferior colliculusRoberto Valdizón-Rodríguez, Dominika Kovaleva, and Paul A. Faure28 June 2019 | Journal of Neurophysiology, Vol. 122, No. 1Tuning for rate and duration of frequency-modulated sweeps in the mammalian inferior colliculusJames A. Morrison, Roberto Valdizón-Rodríguez, Daniel Goldreich, and Paul A. 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Investigated with noise stimuliHearing Research, Vol. 5, No. 2-3Binaural interaction in the inferior colliculus of the frogExperimental Neurology, Vol. 37, No. 3Single unit studies in the midbrain auditory area of CaimanZeitschrift f�r Vergleichende Physiologie, Vol. 71, No. 3Elektro-physiologische Untersuchungen an der H�rbahn der Schleie (Tinca tinca [L.])Zeitschrift f�r Vergleichende Physiologie, Vol. 57, No. 1 More from this issue > Volume 28Issue 6November 1965Pages 1155-1184 https://doi.org/10.1152/jn.1965.28.6.1155PubMed5883734History Published online 1 November 1965 Published in print 1 November 1965 Metrics