The detection of phantom targets in noise by serotine bats; negative evidence for the coherent receiver

Summary Using a target simulator three serotine bats,Eptesicus serotinus, were trained to judge whether a phantom target was present or absent. The echolocation sounds emitted by the bats during the detection were intercepted by a microphone, amplified and returned by a loudspeaker as an artificial echo, with a delay of 3.2 ms and a sound level determined by the overall gain and cry amplitude. The cry level of each pulse was measured and the echo level received by the bat was calculated. The target was presented in 50% of the trials and the gain adjusted using conventional up/down procedures. Under these conditions between 40 and 48 dB peSPL were required for 50% detection (Figs. 2, 3).In a subsequent experiment the phantom target was masked with white noise (N_o) with a spectrum level of –113 dB re. 1 Pa·Hz^–1/2. The thresholds were increased by 7–14 dB. Energy density (S) of a single pulse was measured and used to estimate S/N_o, which ranged from 36–49 dB at threshold. Theoretically the coherent receiver model predicts the ratio between hits and false alarms observed for the bats at a S/N_o of ca. 1–2 dB. Since the bats require 40–50 dB higher S/N_o (Fig. 3), this is taken as negative evidence for coherent reception (cross correlation).Furthermore, a strong sensitivity to clutter was found since there seemed to exist a fixed relationship between thresholds and clutter level.Abbreviations C clutter - Nbw noise in a specified bandwidth - No noise in i Hz bandwidth - peSPL peak equivalent sound pressure level - S signal energy - SD standard deviation - Y/N Yes/No psychometry - 2AFC two alternative forced choice psychometry     

The degradation of distance discrimination in big brown bats (Eptesicus fuscus) caused by different interference signals

The ability of two big brown bats (Eptesicus fuscus) to discriminate the distance to an electronically synthesized phantom target by echolocation was tested in the presence of interfering signals presented slightly before the target echo. Interfering signals were chosen to have differing degrees of similarity to the typical echolocation emission used by the bat in this task (which was the signal used to create the phantom target), and we predicted that the degree of disruption of ranging would be proportional to the similarity of the interference to the target echo. This prediction was not confirmed; rather, all interference signals not identical to the target echo increased the threshold to about twice that found with no interference. When the interference was identical to the target echo, the threshold increased to about 4 times that with no interference. When each bat was presented with phantom target echoes appropriate for the other bat, its range discrimination threshold increased about ten fold, and in this case the degree of interference of different signals was related to their similarity to the target echo, not to their similarity to the bat's normal signal. We suggest that Eptesicus may suppress interference by a more sophisticated strategy than simple linear matched filtering.Abbreviations E exemplar signal - M _f foreign model signal - M _r reversed self-model signal - M _s self-model signal - N noise signal - SPL sound pressure level     

Detection of sonar signals in the presence of pulses of masking noise by the echolocating bat,Eptesicus fuscus

Summary Two big brown bats (Eptesicus fuscus) were trained to report the presence or absence of a virtual sonar target. The bats' sensitivity to transient masking was investigated by adding 5 ms pulses of white noise delayed from 0 to 16 ms relative to the target echo. When signal and masker occurred simultaneously, the bats required a signal energy to noise spectrum level ratio of 35 dB for 50% probability of detection. When the masker was delayed by 2 ms or more there was no significant masking and echo energy could be reduced by 30 dB for the same probability of detection. The average duration of the most energetic sonar signal of each trial was measured to be 1.7 ms and 2.4 ms for the two bats, but a simple relation between detection performance and pulse duration was not found.In a different experiment the masking noise pulses coincided with the echo, and the duration of the masker was varied from 2 to 37.5 ms. The duration of the masker had little or no effect on the probability of detection.The findings are consistent with an aural integration time constant of about 2 ms, which is comparable to the duration of the cries. This is an order of magnitude less than found in backward masking experiments with humans and may be an adaptation to the special constraints of echolocation. The short time of sensitivity to masking may indicate that the broad band clicks of arctiid moths produced as a countermeasure to bat predation are unlikely to function by masking the echo of the moth.Abbreviations SPL sound pressure level - SD standard deviation - SE standard error - BW bandwidth     

Arctiid moth clicks can degrade the accuracy of range difference discrimination in echolocating big brown bats,Eptesicus fuscus

Summary Four big brown bats (Eptesicus fuscus) born and raised in captivity were trained using the Yes/No psychophysical method to report whether a virtual sonar target was at a standard distance or not. At threshold bats were able to detect a minimum range difference of 6 mm (a t of 36 s).Following threshold determinations, a click burst 1.8 ms long containing 5 pulses from the ruby tiger moth, Phragmatobia fuliginosa (Arctiidae), was presented randomly after each phantom echo. The sound energy of the click burst was -4 dB relative to that of the phantom echo. Clicks presented for the very first time could startle naive bats to different degrees depending on the individual.The bats' performance deteriorated by as much as 4000% when the click burst started within a window of about 1.5 ms before the phantom echo (Fig. 4). Even when one of ten phantom echoes was preceded by a click burst, the range difference discrimination worsened by 200% (Fig. 9). Hence, clicks falling within the 1.5 ms time window seem to interfere with the bat's neural timing mechanism.The clicks of arctiid moths appear to serve 3 functions: they can startle naive bats, interfere with range difference determinations, or they can signal the moth's distastefulness, as shown in earlier studies.Abbreviations peSPL peak equivalent sound pressure level - sd standard deviation - FM frequency modulation - CF constant frequency - EPROM erasable programmable read only memory     

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     

Discrimination of insect wingbeat-frequencies by the batRhinolophus ferrumequinum

Summary Five Greater Horseshoe bats,Rhinolophus ferrumequinum, were trained in a two-alternative forced-choice procedure to discriminate between artificial echoes of insects fluttering at different wingbeat rates. The stimuli were electronically produced phantom targets simulating fluttering insects with various wingbeat frequencies (Figs. 3, 4). Difference thresholds for wingbeat rates of 50 Hz and 100 Hz were determined. For an S+ of 50 Hz the difference threshold values lay between 2.8 and 4.6 Hz for individual bats; with an S+ of 100 Hz they increased to between 9.8 and 12.0 Hz (Figs. 5, 6, Table 1).Three bats, previously trained to discriminate between a S+ of 50 Hz and a S– with a lower wingbeat rate, were tested with higher frequency stimuli. When they had to decide between their old S+ of 50 Hz and either a 60 or 70 Hz echo two bats continued to select the 50 Hz stimulus while the third bat now preferred the faster fluttering insects (Table 2).During the discrimination task the echolocation behavior of the bats was monitored. When the phantom targets were presented all bats increased their duty-cycle of sound emission from about 40% to sometimes near 70%. They did so by either emitting longer echolocation calls or by increasing the sound repetition rate (Figs. 7, 8).The results show that Greater Horseshoe bats can determine the wingbeat rate of flying insects with an accuracy between 6 and 12%. Possible cues for flutter rate determination by cf-fm bats from natural and artificial insect echoes are discussed.Abbreviations DC duty-cycle - PD pulse duration - PI pulse interval - cf constantfrequency - fm frequency modulation     

FIELD RECORDINGS OF ECHOLOCATION AND SOCIAL SIGNALS FROM THE GLEANING BAT MYOTIS SEPTENTRIONALIS

ABSTRACT

We recorded echolocation and ultrasonic social signals of the bat Myotis septentrionalis. The bats foraged for insects resting on or fluttering about an outdoor screen to which they were attracted by a ‘backlight’. The bats used nearly linearly modulated echolocation signals of high frequency (117 to 49 kHz, see Tables) with a weak second harmonic. The orientational signals from patrolling bats were about 2.4 ms in duration and occurred at a repetition rate of about 18 Hz (see Figure 3). The signals used by bats as they approached the screen were of shorter duration (0.72 ms) and occurred at higher rates (33.8 Hz) (Table 2 and Figure 4). We registered one feeding ‘buzz’ (Figure 5). We recorded social signals when two bats patrolled the hunting area. The social signals were characterized by their longer durations (6 ms, see Table 1), lower frequencies (70 to 30 kHz), and curvilinear sweeps (Figures 7 and 8). We calculated the source levels of orientational and social signals using the differences in arrival times at three microphones in a linear array (Figures 1 and 2). The source levels were on average 102 dB peSPL at 10 cm (Table 1). We could not calculate source levels of the signals used by bats as they approached the screen at close range, but these signals were much weaker (about 65 dB peSPL at the microphone).     

Prey-Correlated Spectral Changes in Echolocation Sounds of the Indian False Vampire Megaderma lyra

False Vampires ( Megaderma lyra ) are gleaning bats which emit brief (1 ms) and faint echolocation signals consisting of four harmonics of a shallow frequency downward modulated fundamental (27–19 kHz). The complete signal spans a frequency range from 100 to 19 kHz. In sound recordings from three experimental animals we show that Megaderma lyra shifts the dominant frequency in the echolocation signals in relation to the type of prey offered and to flight style. During roaming flights the mean peak frequency was 63.2 ± 9 kHz (third harmonic). In prey catching flights, peak frequencies were shifted into the fourth harmonic. In flights towards a dish of crawling mealworms, mean peak frequency was raised to 91.2 ± 3.3 kHz. When the bats flew towards living mice the dominant frequency was further increased to 99.8 ± 5.2 kHz, and the second and third harmonic were at least 10 dB fainter or no longer recordable. The additional frequency shift when flying towards mice was not only a consequence of the dominance of the fourth harmonic but also of an additional rise of the fundamental harmonic by nearly 2 kHz. These prey-correlated frequency shifts in echolocation calls showed little variation between the three experimental animals and were reproducible over time. They occurred at or even before take-off of the bats. This is the first report of target-correlated transient adaptations in echolocation calls of any bat species.     

Echolocation and obstacle avoidance in the hipposiderid batAsellia tridens

Summary 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.The sound duration in roosting and free flying bats is between 7–10 ms. In the approach and terminal phase of bats landing on a perch or flying through obstacles, the sound duration is reduced and the repetition rate increased the nearer the bat approaches the target. At the end of the terminal phase sound durations of a minimum of 3 ms have been measured. Flying bats lower their emission frequency in order to compensate for Doppler shifts caused by the flight movement. The echofrequency is therefore kept constant about 150–200 Hz above the resting frequency.In flights through obstacles consisting of vertically stretched wires with different diameters, the bats were able to avoid wires down to a diameter of 0.065 mm whereas at 0.05 mm the percentage of flights without collisions is far below the chance level. The results demonstrate that the echolocation behavior of the hipposiderid batAsellia tridens does not differ fundamentally from that of rhinolophid bats. As a result, a new suggestion for categorization of bats producing cf-fm orientation sounds is put forward.Abbreviations cf constant frequency component - fm frequency modulated component - P probability of collision-free flights through an obstacle of ertically tretched wires - I interval between wires - D minimal diameter of a bat with folded wings; , angle at which a bat approaches an obstacle - f _A frequency of the cf-component of the emitted sound - f _E frequency of the cf-component of the echo - f _M frequency of the cf-component of the sounds recorded with the microphone - c speed of sound Supported by the Deutsche Forschungsgemeinschaft grant no. Schn 138/6-9We thank W. Hollerbach for technical assistance.     

Labile cochlear tuning in the mustached bat

Summary Acoustic stimuli near 60 kHz elicit pronounced resonance in the cochlea of the mustached bat (Pteronotus parnellii parnellii). The cochlear resonance frequency (CRF) is near the second harmonic, constant frequency (CF2) component of the bat's biosonar signals. Within narrow bands where CF2 and third harmonic (CF3) echoes are maintained, the cochlea has sharp tuning characteristics that are conserved throughout the central auditory system. The purpose of this study was to examine the effects of temperature-related shifts in the CRF on the tuning properties of neurons in the cochlear nucleus and inferior colliculus.Eighty-two single and multi-unit recordings were characterizedin 6 awake bats with chronically implanted cochlear microphonic electrodes. As the CRF changed with body temperature, the tuning curves of neurons sharply tuned to frequencies near the CF2 and CF3 shifted with the CRF in every case, yielding a change in the unit's best frequency. The results show that cochlear tuning is labile in the mustached bat, and that this lability produces tonotopic shifts in the frequency response of central auditory neurons. Furthermore, results provide evidence of shifts in the frequency-to-place code within the sharply tuned CF2 and CF3 regions of the cochlea. In conjunction with the finding that biosonar emission frequency and the CRF shift concomitantly with temperature and flight, it is concluded that the adjustment of biosonar signals accommodates the shifts in cochlear and neural tuning that occur with active echolocation.Abbreviations BF best frequency - CF characteristic frequency - CF2, CF3 second and third harmonic, constant frequency components of the biosonar signal - CM cochlear microphonic - CN cochlear nucleus - CRF cochlear resonance frequency - IC inferior colliculus - MT minimum threshold - OAE otoacoustic emission - Q_10dB BF (or CF) divided by the response bandwidth at 10 dB above MT     

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     

Modelling simultaneous echo waveform reconstruction and localization in bats

Echolocating bats perceive the world through sound signals reflecting from the objects around them. In these signals, information is contained about reflector location and reflector identity. Bats are able to extract and separate the cues for location from those that carry identification information. We propose a model based on Wiener deconvolution that also performs this separation for a virtual system mimicking the echolocation system of the lesser spearnosed bat, Phyllostomus discolor. In particular, the model simultaneously reconstructs the reflected echo signal and localizes the reflector from which the echo originates. The proposed technique is based on a model that performs a similar task based on information from the frog’s lateral line system. We show that direct application of the frog model to the bat sonar system is not feasible. However, we suggest a technique that does apply to the bat biosonar and indicate its performance in the presence of noise.     

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     

Ontogenesis of auditory fovea representation in the inferior colliculus of the Sri Lankan rufous horseshoe bat,Rhinolophus rouxi

Summary This report describes the ontogenesis of tonotopy in the inferior colliculus (IC) of the rufous horseshoe bat (Rhinolophus rouxi). Horseshoe bats are deaf at birth, but consistent tonotopy with a low-to-high frequency gradient from dorsolateral to ventromedial develops from the 2nd up to the 5th week. The representation of the auditory fovea is established in ventro-mediocaudal parts of the IC during the 3rd postnatal week (Fig. 3). Then, a narrow frequency band 5 kHz in width, comprising 16% of the bat's auditory range, captures 50–60 vol% of the IC (Fig. 3c). However, foveal tuning is 10–12 kHz (1/3 octave) lower than in adults; foveal tuning in females (65–68 kHz) is 2–3 kHz higher than in males (62–65 kHz). Thereafter, foveal tuning increases by 1–1.5 kHz per day up to the 5th postnatal week, when the adult hearing range is established (Figs. 4, 5). The increase of sensitivity and of tuning sharpness of single units also follows a low-to-high frequency gradient (Fig. 6).Throughout this development the foveal tuning matches the second harmonic of the echolocation pulses vocalised by these young bats. The results confirm the hypothesis of developmental shifts in the frequency-place code for the foveal high frequency representation in the IC.Abbreviations BF best frequency - CF constant frequency - FM frequency modulation - IC inferior colliculus - IHC inner hair cell; - OHC outer hair cell - RR Rhinolophus rouxi     

Click-based echolocation in bats: not so primitive after all

Echolocating bats of the genus Rousettus produce click sonar signals, using their tongue (lingual echolocation). These signals are often considered rudimentary and are believed to enable only crude performance. However, the main argument supporting this belief, namely the click’s reported long duration, was recently shown to be an artifact. In fact, the sonar clicks of Rousettus bats are extremely short, ~50–100 μs, similar to dolphin vocalizations. Here, we present a comparison between the sonar systems of the ‘model species’ of laryngeal echolocation, the big brown bat (Eptesicus fuscus), and that of lingual echolocation, the Egyptian fruit bat (Rousettus aegyptiacus). We show experimentally that in tasks, such as accurate landing or detection of medium-sized objects, click-based echolocation enables performance similar to laryngeal echolocators. Further, we describe a sophisticated behavioral strategy for biosonar beam steering in clicking bats. Finally, theoretical analyses of the signal design—focusing on their autocorrelations and wideband ambiguity functions—predict that in some aspects, such as target ranging and Doppler-tolerance, click-based echolocation might outperform laryngeal echolocation. Therefore, we suggest that click-based echolocation in bats should be regarded as a viable echolocation strategy, which is in fact similar to the biosonar used by most echolocating animals, including whales and dolphins.     

Integration time for short broad band clicks in echolocating FM-bats (Eptesicus fuscus)

Vespertilionid FM-bats (four Eptesicus fuscus and one Vespertilio murinus) were trained in an electronic phantom target simulator to detect synthetic echoes consisting of either one or two clicks. The threshold sound pressure for single clicks was around 47 dB peSPL for all five bats corresponding to a threshold energy of -95 dB re 1 Pa² * s. By varying the interclick interval, T, for double clicks it was shown that the threshold intensity was around — 3 dB relative to the threshold for single clicks at T up to 2.4 ms, indicating perfect power summation of both clicks. A threshold shift of -13.5 dB for a 1 ms train of 20 clicks (0.05 ms interclick interval) confirmed that the bats integrated the power of the stimuli. At T longer than around 2.5 ms the threshold for double clicks was the same as for single clicks. Thus, the bats performed like perfect energy detectors with an integration time of approximately 2.4 ms. This integration time is an order of magnitude shorter than that reported for bats listening passively for pure tones. In our setup the bats emitted sonar signals with durations of 2–3 ms. Hence, the results may indicate that while echolocating the bats integration time is adapted to the duration of the sonar emissions.Abbreviations AGC automatic gain control - FM frequency modulated - peSPL peak equivalent sound pressure level - rms root mean square - SD standard deviation - SE standard error of mean - T interclick interval     

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     

Classification of insects by echolocating greater horseshoe bats

Summary Echolocating greater horseshoe bats (Rhinolophus ferrumequinum) detect insects by concentrating on the characteristic amplitude- and frequency modulation pattern fluttering insects impose on the returning echoes. This study shows that horseshoe bats can also further analyse insect echoes and thus recognize and categorize the kind of insect they are echolocating.Four greater horseshoe bats were trained in a twoalternative forced-choice procedure to choose the echo of one particular insect species turning its side towards the bat (Fig. 1). The bats were able to discriminate with over 90% correct choices between the reward-positive echo and the echoes of other insect species all fluttering with exactly the same wingbeat rate (Fig. 4).When the angular orientation of the reward-positive insect was changed (Fig. 2), the bats still preferred these unknown echoes over echoes from other insect species (Fig. 5) without any further training. Because the untrained bats did not show any prey preference, this indicates that the bats were able to perform an aspect-anglein-dependent classification of insects.Finally we tested what parameters in the echo were responsible for species recognition. It turned out that the bats especially used the small echo-modulations in between glints as a source of information (Fig. 7). Neither the amplitudenor the frequencymodulation of the echoes alone was sufficient for recognition of the insect species (Fig. 8). Bats performed a pattern recognition task based on complex computations of several acoustic parameters, an ability which might be termed cognitive.Abbreviations AM amplitude modulation - CF constant frequency - FM frequency modulation - S+ positive stimulus - S- negative stimulus     

大蹄蝠回声定位信号特征与下丘神经元频率调谐

采用超声监测仪录制超声信号和细胞外电生理记录下丘神经元的频率调谐曲线(frequency tuningcurqes,FTCs)的方法,探讨了大蹄蝠(Hipposideros armiger)回声定位信号与下丘(inferior colliculus,IC)神经元频率调谐之间的相关性.结果发现,大蹄蝠回声定位叫声为恒频-调频(consrant frequency-frequenevmodulated,CF-FM)信号,一般含有2-3个谐波,第二谐波为其主频,cF成分频率(Mean±SD,n=18)依次为:(33.3 4±0.2)、(66.5±0.3)、(99.4 4±0.5)kHz;电生理实验共获得72个神经元的频率调谐曲线,Q10-dB值的范围是0.5-95.4(9.2±14.6,rg=72),最佳频率(best frequency,BF)在回声定位主频附近的神经元具有尖锐的频率调谐特性.结果表明,大蹄蝠回声定位信号与下丘神经元频率调谐存在相关性,表现为最佳频率在回声定位信号主频附近的神经元频率调谐曲线的Q10-dB值较大,具有很强的频率分析能力.