Frequency tracking and Doppler shift compensation in response to an artificial CF/FM echolocation sound in the CF/FM bat,Noctilio albiventris

Summary Bats of the speciesNoctilio albiventris emit short-constant frequency/frequency modulated (short-CF/FM) pulses with a CF component frequency at about 75 kHz. Bats sitting on a stationary platform were trained to discriminate target distance by means of echolocation. Loud, free-running artificial pulses, simulating the bat's natural CF/FM echolocation sounds or with systematic modifications in the frequency of the sounds, were presented to the bats during the discrimination trials. When the CF component of the artificial CF/FM sound was between 72 and 77 kHz, the bats shifted the frequency of the CF component of their own echolocation sounds toward that of the artificial pulse, tracking the frequency of the artificial CF component.Bats flying within a large laboratory flight cage were also presented with artificial pulses. Bats in flight lower the frequency of their emitted pulses to compensate for Doppler shifts caused by their own flight speed and systematically shift the frequency of their emitted CF component so that the echo CF frequency returns close to that of the CF component of the artificial CF/FM pulse, over the frequency range where tracking occurs.Abbreviations CF constant frequency - FM frequency modulation     

A gating mechanism for sound pattern recognition is correlated with the temporal structure of echolocation sounds in the rufous horseshoe bat

Summary The rufous horseshoe bat, Rhinolophus rouxi, was trained to discriminate differences in target distance. Loud free running artificial pulses, simulating the bat's natural long-CF/FM echolocation sounds, interfered with the ability of the bat to discriminate target distance. Interference occurred when the duration of the CF component of the CF/FM artificial pulse was between 2 and 70 ms. A brief (2.0 ms) CF signal 2–68 ms before an isolated FM signal was as effective as a continuous CF component of the same duration. When coupled with the bat's own emissions, a 2 ms FM sweep alone was effective in interfering when it came 42 to 69 ms after the onset of the bat's pulse. The coupled FM artificial pulses did not interfere when they began during the bat's own emissions.It appears that the onset of the CF component activates a gating mechanism that establishes a time window during which FM component signals must occur for proper neural processing. A comparison with a similar gating mechanism in Noctillo albiventris, which emits short-CF/FM echolocation sounds, reveals that the temporal parameters of the time window of the gating mechanism are species specific and specified by the temporal structure of the echolocation sound pattern of each species.Abbreviations FM frequency modulated - CF constant frequency     

Discrimination performance and echolocation signal integration requirements for target detection and distance determination in the CF/FM bat,Noctilio albiventris

Summary Bats of the speciesNoctilio albiventris were trained to detect the presence of a target or to discriminate differences in target distance by means of echolocation. During the discrimination trials, the bats emitted pairs of pulses at a rate of 7–10/s. The first was an 8 ms constant frequency (CF) signal at about 75 kHz. This was followed after about 28 ms by a short-constant frequency/ frequency modulated (short-CF/FM) signal composed of a 6 ms CF component at about 75 kHz terminating in a 2 ms FM component sweeping downward to about 57 kHz. There was no apparent difference in the pulse structure or emission pattern used for any of the tasks. The orientation sounds of bats flying in the laboratory and hunting prey under natural conditions follow the same general pattern but differ in interesting ways.The bats were able to discriminate a difference in target distance of 13 mm between two simultaneously presented targets and of 30 mm between single sequentially presented targets around an absolute distance of 35 cm, using a criterion of 75% correct responses.The bats were unable to detect the presence of the target or to discriminate distance in the presence of continuous white noise of 54 dB or higher SPL. Under conditions of continuous white noise, the bats increased their pulse repetition rate and the relative proportion of CF/FM pulses.The bats required a minimum of 1–2 successive CF/FM pulse-echo pairs for target detection and 2–3 to discriminate a 5 cm difference in distance. When the distance discrimination tasks were made more difficult by reducing the difference in distance between the two targets the bats needed to integrate information from a greater number of successive CF/FM pulse-echo pairs to make the discrimination.Abbreviations CF constant frequency - FM frequency modulation     

Harmonic and frequency structure used for echolocation sound pattern recognition and distance information processing in the rufous horseshoe bat

Summary The rufous horseshoe bat, Rhinolophus rouxi, was trained to discriminate differences in target distance. During the discrimination trials, the bats emitted complex FM/CF/FM pulses containing first harmonic and dominant second harmonic components.Loud free running artificial pulses, simulating the CF/FM part of the natural echolocation components, interfered with the ability of the bat to discriminate target distance. Changes in the frequency or frequency pattern of the artificial pulses resulted in systematic changes in the degree of interference. Interference occurred when artificial CF/FM pulses were presented at frequencies near those of the bat's own first or second harmonic components.These findings suggest that Rhinolophus rouxi uses both the first and second harmonic components of its complex multiharmonic echolocation sound for distance discrimination. For interference to occur, the sound pattern of each harmonic component must contain a CF signal followed by an FM sweep beginning near the frequency of the CF.Abbreviations CF constant frequency - FM frequency modulated     

Complex sound analysis in the lesser bulldog bat: evidence for a mechanism for processing frequency elements of frequency modulated signals over restricted time intervals

A stereotypical approach phase vocalization response of the lesser bulldog bat, Noctilio albiventris, to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bat was not significantly different when presented with naturally structured CF/FM echoes containing FM elements that sweep continuously from about 75-55 kHz in 4 ms or with CF/FM echoes containing FM components constructed from a series of 98 pure tone frequency steps, each with a duration of 0.04 ms. The performance of the bat remained unchanged when the duration of the tone steps was increased up to 0.08 ms but declined sharply to a level that was significantly below that seen with a naturally structured echo when the steps were 0.09 ms or longer. The performance of the bat depended on the duration of the individual tone steps, which could not exceed a specific upper limit of about 0.08 ms. The study suggests that the bats have adaptations for processing individual narrow band segments of FM signals over specific time intervals.Abbreviations CF constant frequency - FM frequency modulation     

Echolocation by the long-eared bat,Plecotus phyllotis

Summary The echolocating bat,Plecotus phyllotis (Vespertilionidae), uses long-CF/FM and FM sonar sounds in different situations. The CF component in long-CF/FM sounds occurs at 27 kHz and has a duration of 20 to 200 ms. The FM component sweeps down from 24 to 12 kHz, with a prominent second harmonic from 40 to 22 kHz. This second harmonic sweep is interrupted at 28 to 25 kHz, providing a notch in the spectrum of the FM component at the CF frequency. This notch probably permits isolation of CF and FM components in echoes for separate processing, thus avoiding mutual interference with the different kinds of target information the two components convey. The FM component is also used without the CF component as a sonar sound. Two other FM orientation sounds are used when the bat is in a confined space such as a room. One contains only the second and fourth harmonics of the 24 to 12 kHz fundamental sweep, while the other contains only the fifth harmonic. This bat's repertoire of sonar sounds closely matches the hearing capacities of the genus.We thank P.H. Dolkart and W.A. Lavender, of Washington University, and the Nevada State Parks Department for their assistance. This research was supported by Grant # BMS-72-02351-A01 from the National Science Foundation.     

Frequency modulated sound pattern analysis in the lesser bulldog bat: the role of interactions between adjacent frequency elements of complex sounds

A stereotyped approach phase vocalization response of Noctilio albiventris to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bats depended on the temporal pattern of frequency change of the continuously sweeping frequency modulated (FM) component of the signals. When the bats were presented with a CF/FM signal containing a time-reversed upward FM sweep, they responded with approach phase behavior at a performance level that was significantly below that seen with a CF/FM signal containing a naturally structured downward FM sweep. When the FM sweep was divided into a series of brief pure tone steps, the extent to which the bats showed a difference in their capability to process upward versus downward FM sweeps depended on the difference in frequency between the pure tone steps. The bats effectively processed downward but not upward FM sweeps when the difference in frequency between pure tone frequency elements of the FM sweeps was from about 100–200 Hz, but they effectually processed both downward and upward FM sweeps when the tonal elements composing the FM sweeps were separated by more than about 200 Hz. This suggests that the ability of the bats to effectively process downward but not upward FM sweeps is based on local interactions between adjacent frequency elements of the complex sounds.Abbreviations CF constant frequency - FM frequency modulated     

A neural mechanism for detecting the distance of a selected target by modulating the FM sweep rate of biosonar in echolocation of bat

Most species of bats making echolocation use frequency modulated (FM) ultrasonic pulses to measure the distance to targets. These bats detect with a high accuracy the arrival time differences between emitted pulses and their echoes generated by targets. In order to clarify the neural mechanism for echolocation, we present neural model of inferior colliculus (IC), medial geniculate body (MGB) and auditory cortex (AC) along which information of echo delay times is processed. The bats increase the downward frequency sweep rate of emitted FM pulse as they approach the target. The functional role of this modulation of sweep rate is not yet clear. In order to investigate the role, we calculated the response properties of our models of IC, MGB, and AC changing the target distance and the sweep rate. We found based on the simulations that the distance of a target in various ranges may be encoded the most clearly into the activity pattern of delay time map network in AC, when the sweep rate of FM pulse used is coincided with the observed value which the bats adopt for each range of target distance.     

Echolocation sounds and hearing of the greater Japanese horseshoe bat (Rhinolophus ferrumequinum nippon)

Summary The relationship between the orientation sounds and hearing sensitivity in the greater Japanese horseshoe bat,Rhinolophus ferrumequinum nippon was studied.An orientation pulse consisted of a constant frequency (CF) component followed by a short downward frequency-modulated (FM) component. Sometimes, an initial upward FM component preceded the CF component. Duration of pulses was about 30 ms and the CF of resting pulses (RF) averaged 65.5 kHz. The best frequency (BF) at the lowest threshold in audiograms as measured by the pinna reflex averaged 66.1 kHz. Audiograms showed remarkable sharp cut-offs on both sides near the BF. The frequency difference between the BF and the RF was about 0.6 kHz, and the RF was always below the BF. The values of RF and BF were characteristically different from those of the European subspecies,Rhinolophus ferrumequinum ferrumequinum.Abbreviations BF best frequency - CF constant frequency - FM frequency modulated - RF resting frequency     

The echolocation and hunting behavior of the bat,Pipistrellus kuhli

Summary The echolocation and hunting behavior ofPipistrellus kuhli was studied in the field using multi-exposure photography synchronized with high-speed tape recordings. During the search phase, the bats used 8–12 ms signals with sweeps (sweep width 3–6 kHz) and pulse intervals near 100 ms or less often near 200 ms (Figs. 1 and 2). The bats seemed to have individual terminal frequencies that could lie between 35 and 40 kHz. The duty cycle of searching signals was about 8%. The flight speed of hunting bats was between 4.0 and 4.5 m/s. The bats reacted to insect prey at distances of about 70 to 120 cm. Given the flight speed, the detection distance was estimated to about 110 to 160 cm. Following detection the bat went into the approach phase where the FM sweep steepened (to about 60 kHz bandwidth) and the repetition rate increased (to about 30 Hz). The terminal phase or buzz, which indicates prey capture (or attempted capture), was composed of two sections. The first section contained signals similar to those in the approach phase except that the pulse duration decreased and the repetition rate increased. The second section was characterized by a sharp drop in the terminal frequency (to about 20 kHz) and by very short pulses (0.3 ms) at rates of up to 200 Hz (Figs. 1 and 3). Near the beginning of the buzz the bat prepared for capturing the prey by extending the wings and forming a tail pouch (Fig. 4). A pause of about 100 ms in sound emission after the buzz indicated a successful capture (Fig. 4). Pulse duration is discussed in relation to glint detection and detection distance. It is argued that the minimum detection distance can be estimated from the pulse duration as the distance where pulse-echo overlap is avoided.Abbreviations CF constant frequency - FM frequency modulated     

Discrimination of wingbeat motion by bats,correlated with echolocation sound pattern

Summary Bats of the species Rhinolophus rouxi, Hipposideros lankadiva and Eptesicus fuscus were trained to discriminate between two simultaneously presented artificial insect wingbeat targets moving at different wingbeat rates. During the discrimination trials, R. rouxi, H. lankadiva and E. fuscus emitted long-CF/FM, short-CF/FM and FM echolocation sounds respectively. R. rouxi, H. lankadiva and E. fuscus were able to discriminate a difference in wingbeat rate of 2.7 Hz, 9.2 Hz and 15.8 Hz, respectively, between two simultaneously presented targets at an absolute wingbeat rate of 60 Hz, using a criterion of 75% correct responses.The performance of the different bat species is correlated with the echolocation signal design used by each species, particularly with the presence and relative duration of a narrowband component preceding a broadband FM component. These results provide behavioral evidence supporting the hypothesis that bats that use CF/FM echolocation sounds have adaptations for the perception of insect wingbeat motion and that long-CF/FM species are more specialized for this task than short-CF/FM species.Abbreviations CF constant frequency - FM frequency modulation     

Echolocation behaviours of the Japanese pipistrelle batPipistrellus abramus during foraging flight

The acoustic structure of echolocation pulses emitted by Japanese pipistrellePipistrellus abramus (Temminck, 1840) bats during different phases of aerial hawking is described here for the first time. Behavioural observations of the foraging flight in conjunction with acoustical analysis of echolocation pulses indicated a flight path consisting of four distinct phases following the reconnaissance or search phase. Short (∼4.68 ms) and relatively broadband frequencymodulated (FM) pulses (∼23.55 kHz bandwidth) were emitted at a repetition rate of 15 Hz during presumed target approach. Presumed insect capture consisted of an early and a late buzz phase. Both buzz types were emitted at high repetition rates (111 Hz in early to 222 Hz in late) and consisted of very short, broadband FM pulses (1.26 ms in early to 0.3 ms in late). There was also a characteristically sharp drop in both the peak and terminal frequencies of each echolocation pulse during the transition from early to late buzz. No pulses were recorded during the final phase of foraging referred to as a “post-buzz pause”. Thus the foraging behaviour of this species consisted of five sequential phases involving four broad types of echolocation pulses.     

Audiovocal interactions during development? Vocalisation in deafened young horseshoe bats vs. audition in vocalisation-impaired bats

Summary Horseshoe bats (Rhinolophus rouxi) were deafened in their 3rd–5th postnatal week. Subsequently their vocalisations were monitored to evaluate the impact of audition on the development of echolocation pulses. Hearing impairment affected the echolocation pulses as follows: the frequency of the constant frequency (CF) component was altered by between + 4 kHz and – 14 kHz, and the dominance of the second harmonic of the pulses was neutralised by a relative increase in intensity of the first and third harmonics.A second experiment focused on possible influences of acoustical self-stimulation with echolocation pulses on the establishment of auditory fovea representation in the inferior colliculus (IC). Frequency control of echolocation pulses was disrupted by larynx denervation. Thereafter, the bats produced multiharmonic echolocation signals (4–11 harmonics) varying in frequency. IC tonotopy, however, as monitored by stereotaxic electrophysiology, showed the same developmental dynamics as seen in control specimens (Fig. 10).Both experiments indicate that throughout postnatal development echolocation pulses are under auditory feedback control, whereas maturation of the auditory fovea and shifts in its frequency tuning represent an innate process. The significance of this postnatal development might be the adjustment of the vocal motor system of each bat to the frequency of its personal auditory fovea.Abbreviations CF constant frequency - CF1, CF2, CF3 harmonics of pure tone components of the echolocation pulses - FM frequency modulation - IC inferior colliculus of the midbrain     

Frequency discrimination of brief tonal steps as a function of frequency in the lesser bulldog bat

In a two-alternative, forced-choice task lesser bulldog bats were trained to distinguish between a pure tone pulse and a pulse composed of a series of brief tonal steps oscillating between two different frequencies. The tone-step pulse gradually approximates the pure tone pulse as the frequency difference between the steps becomes progressively smaller. Frequency difference limens for the brief tonal frequency steps were determined for a broad range of ultrasonic frequencies. The variation in tone-step difference limens with frequency appears to be correlated to the frequency structure of the bat's short-constant-frequency/frequency-modulated echolocation sound. There was a marked decline in the value of the relative frequency difference limens (Weber ratio) over a fairly narrow range of frequencies above the constant frequency and a sharp increase in threshold above this range. The relative thresholds for frequency discrimination were small and uniform over the frequency range of the frequency-modulated sweep and increased for frequencies below the frequency- modulated sweep. Thus, the most accurate frequency-discrimination abilities occur over a narrow frequency range around the frequency of the constant-frequency component of returning echoes. Frequency discrimination over the range of frequencies of the frequency-modulated component is relatively good. Accepted: 20 March 1999     

FM signals produce robust paradoxical latency shifts in the bat’s inferior colliculus

Previous studies in echolocating bats, Myotis lucifugus, showed that paradoxical latency shift (PLS) is essential for neural computation of target range and that a number of neurons in the inferior colliculus (IC) exhibit unit-specific PLS (characterized by longer first-spike latency at higher sound levels) in response to tone pulses at the unit’s best frequency. The present study investigated whether or not frequency-modulated (FM) pulses that mimic the bat’s echolocation sonar signals were equally effective in eliciting PLS. For two-thirds of PLS neurons in the IC, both FM and tone pulses could elicit PLS, but only FM pulses consistently produced unit-specific PLS. For the remainder of PLS neurons, only FM pulses effectively elicited PLS; these cells showed either no PLS or no response, to tone pulses. PLS neurons generally showed more pronounced PLS in response to narrow-band FM (each sweeping 20 kHz in 2 ms) pulse that contained the unit’s best frequency. In addition, almost all PLS neurons showed duration-independent PLS to FM pulses, but the same units exhibited duration-dependent PLS to tone pulses. Taken together, when compared to tone pulses, FM stimuli can provide more reliable estimates of target range.     

Ultrasonic bouts of a blind climbing rodent (Typhlomys chapensis): acoustic analysis

ABSTRACT

The peculiar acoustic structure of ultrasonic bouts of blind climbing rodents Typhlomys might provide insight on their potential function. We examined 1481 bouts consisting of 1-6 pulses; 49.7% of them were single-pulse bouts. Bout duration and inter-bout interval depended on the number of pulses per bout, whereas period from start of a previous bout to start of the next bout was constant (80.0±2.9 ms). Ultrasonic pulses (540 pulses measured in a subset of 234 bouts) were short (0.68±0.15 ms) sweeps with fundamental frequency slopes from 127.3±6.3 kHz to 64.1±4.6 kHz and peak frequency at 93.3±7.4 kHz, emitted within bouts with inter-pulse periods of 13.03±3.01 ms. Single pulses and start pulses of multi-pulse bouts were lower in frequency than other pulses of the bouts. In contrast, pulse duration was independent on pulse position within bout. Pulses of Typhlomys were reminiscent of echolocation calls of Murina and Myotis bats, but higher in frequency, much shorter, fainter, displayed a convex contour of frequency modulation and only the fundamental frequency band without harmonics and were organized in bouts, that is not characteristic for bat echolocation. Most probably, Typhlomys uses their ultrasonic pulses for call-based orientation during locomotion, including climbing and jumping among bush branches.     

Echolocation calls of free-flying common vampire bats Desmodus rotundus (Chiroptera: Phyllostomidae) in Chile

We recorded and characterized the echolocation calls emitted by the common vampire bat Desmodus rotundus during foraging in natural habitats in Chile. Signal design typically shows multiple harmonics consisting of a brief quasi-constant frequency (QCF) component at the beginning of the pulse followed by a downward frequency modulated component. Calls are characterized by long durations (5.5 ms) and emitted as single pulses or in groups of 2–3 pulses at a repetition rate of 29 Hz. The higher frequency ranges (85–35 kHz) and the unusual QCF component that characterized multiharmonic signals of free-flying D. rotundus in Chile is a remarkable feature for acoustic identification with other Chilean bats.     

无尾蹄蝠的回声定位声波特征及分析

采用超声波监听仪U30录制无尾蹄蝠自由飞行状态的回声定位声波,经Batsound3.0分析,其声波为高频(145.4±10.9kHz)、宽带(62.6±9.2kHz)、具两个谐波的短(1.67±0.4ms)FM型,不同于蹄蝠科其他蝙蝠的CF型,表明该科内物种声波类型存在多态性。头骨的形态测定分析支持其通过鼻腔发射声波,与蹄蝠科其他蝙蝠一致,表明该科内声波发射方式的单一性。适应环境的选择压力及翼型和声波的适应性可能是其选择FM型叫声的重要原因。     

Responses to pure tones and linear FM components of the CF — FM biosonar signal by single units in the inferior colliculus of the mustached bat

The responses of 682 single-units in the inferior colliculus (IC) of 13 mustached bats (Pteronotus parnellii parnellii) were measured using pure tones (CF), frequency modulations (FM) and pairs of CF-FM signals mimicking the species' biosonar signal, which are stimuli known to be essential to the responses of CF/CF and FM-FM facilitation neurons in auditory cortex. Units were arbitrarily classified into 'reference frequency' (RF), 'FM2' and 'Non-echolocation' (NE) categories according to the relationship of their best frequencies (BF) to the biosonar signal frequencies. RF units have high Q10dB values and are tuned to the reference frequency of each bat, which ranged between 60.73 and 62.73 kHz. FM2 units had BF's between 50 and 60 kHz, while NE units had BF's outside the ranges of the RF and FM2 classes. PST histograms of the responses revealed discharge patterns such as 'onset', 'onset-bursting' (most common), 'on-off', 'tonic-on','pauser', and 'chopper'. Changes in discharge patterns usually resulted from changes in the frequency and/or intensity of the stimuli, most often involving a change from onset-bursting to on-off. Different patterns were also elicited by CF and FM stimuli. Frequency characteristics and thresholds to CF and FM stimuli were measured. RF neurons were very sharply tuned with Q10dB's ranging from 50-360. Most (92%) also responded to FM2 stimuli, but 78% were significantly more sensitive (greater than 5 dB) to CF stimuli, and only 3% had significantly lower thresholds to FM2. The best initial frequency for FM2 sweeps in RF units was 65.35 +/- 2.138 kHz (n = 118), well above the natural frequency of the 2nd harmonic. FM2 and NE units were indistinguishable from each other, but were quite different from RF units: 41% of these two classes had lower thresholds to CF, 49% were about equally sensitive, and 10% had lower thresholds to FM. For FM2 units, mean best initial frequency for FM was 60.94 kHz +/- 3.162 kHz (n = 114), which is closely matched to the 2nd harmonic in the biosonar signal. Very few units (5) responded only to FM signals, i.e., were FM-specialized. The characteristics of spike-count functions were determined in 587 units. The vast majority (79%) of RF units (n = 228) were nonmonotonic, and about 22% had upper-thresholds.(ABSTRACT TRUNCATED AT 400 WORDS)     

Complex sound analysis in the FM bat Eptesicus fuscus,correlated with structural parameters of frequency modulated signals

Big brown bats, Eptesicus fuscus, were presented with artificial frequency modulated (FM) echoes that simulated an object becoming progressively closer to the bat. A stereotyped approach phase behavioral response of the bat to the virtual approaching target was used to determine the ability of the bat to analyze FM signals for target distance information. The degree to which the bats responded with approach phase behavior to a virtual approaching target was similar when they were presented with either a naturally structured artificial FM echo or an artificial FM echo constructed from a series of brief pure tone steps. The ability of the bats to respond to an FM signal structured from a sequence of pure tone elements depended on the number of pure tone steps in the series; the bats required the presentation of tone-step FM signals containing about 83 or greater pure tone elements. Moreover, the duration of the individual tone steps of the tone-step FM signals could not exceed a specific upper limit of about 0.05 ms. Finally, it appears that the bats were able to independently resolve individual tone steps within the tone-step FM signals that were separated by about 450 Hz or more.Abbreviations CF constant frequency - FM frequency modulation