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PubMedDate not supplied

[Correlation model of object recognition by echolocating animals].

The model proposed in an attempt to find out physical bases of object perception during echolocation. It is shown that echolocational perception can be provided with correlational treatment of corresponding signals. The character of objects is determined by the comparison by echo probing accepted in the given cycle with typical distortions remembered in the course of individual experience of the animal. The distortions take place during the reflection of the probing impulse from these or those objects. "Binding" of the objects according to distance may be carried out by using the choice of typical distortions for corresponding correction of the copy of probing impulse, serving as a bearing signal of distance correlometer. The response of correlometer to the echo from correctly perceived target increases. The block-scheme of such correlation perception during echolocation is given. Performance of some experiments allowing to check and refine the model considered.

Animals↗
PubMed1990

Matching-to-sample by an echolocating dolphin (Tursiops truncatus).

An adult male dolphin was trained to perform a three-alternative delayed matching-to-sample task while wearing eyecups to occlude its vision. Sample and comparison stimuli consisted of a small and a large PVC plastic tube, a water-filled stainless steel sphere, and a solid aluminum cone. Stimuli were presented under water and the dolphin was allowed to identify the stimuli through echolocation. The echolocation clicks emitted by the dolphin to each sample and each comparison stimulus were recorded and analyzed. Over 48 sessions of testing, choice accuracy averaged 94.5% correct. This high level of accuracy was apparently achieved by varying the number of echolocation clicks emitted to various stimuli. Performance appeared to reflect a preexperimental stereotyped search pattern that dictated the order in which comparison items were examined and a complex sequential-sampling decision process. A model for the dolphin's decision-making processes is described.

Animals↗
PubMedDate not supplied

[Calculation of potential accuracy in measuring the angular coordinates of targets by the echolocator of bats using the equal-signal zone method].

Potential accuracy in measuring the course to a target is calculated. This accuracy is physically achievable it the hypothesis that an accurate measurement of angular coordinates of the target of bat's echolocator is realized by the method similar to that of equally signaling zone in radiolocation is true. Possible application of such a method is based on the "pulsation" of direction diagram in the course of radiation of the probing impulse. In this case crossing of partial diagrams of radiation corresponding to high- and low-frequancy regions of the impulse form the equally signaling zine. If the target is in this direction the amplitudes of autocorrelation functions formed by corresponding regions of reflected and probing impulses will be equal. The minimal error of the method is limited by the optimum duration of each of the compared correlation functions, which forms the basis for derivation of the formula evaluating this error. Numerical calculation of the accuracy of measurements of the angle achievable for the echolocator of Myotis blythi is performed by this formula proceeding from average experimental values of the echolocator characteristics. The model under consideration is shown to agree with a number of experimental data.

Animals↗
PubMed2002

A neural network model of the inferior colliculus with modifiable lateral inhibitory synapses for human echolocation.

We propose a neural network model of the inferior colliculus (IC) for human echolocation. Neuronal mechanisms for human echolocation were investigated by simulating the model. The model consists of the neural networks of the central nucleus (ICc) and external nucleus (ICx) of the inferior colliculus. The neurons of the ICc receive interaural sound stimuli via multiple contralateral delay lines and a single ipsilateral delay line. The neurons of the ICc send output signals to the neurons of the ICx in a convergent manner. We stimulated the ICc with pairs of a direct sound (a sonar sound) and an echo sound (the reflection from an object). Information about the distance between the model and the object is expressed by the delay time of the echo sound with respect to the direct sound. The results presented here show that neurons of the ICc responsive to interaural onset time differences contribute to the creation of an auditory distance map in the ICx. We trained the model with various pairs of direct-echo sounds and modified synaptic connection strengths of the networks according to the Hebbian rule. It is shown that self-organized long-term depression of lateral inhibitory synaptic connections plays an important role in enhancing echolocation skills.

Acoustic Stimulation↗
PubMed2001

Integrated fossil and molecular data reconstruct bat echolocation.

Molecular and morphological data have important roles in illuminating evolutionary history. DNA data often yield well resolved phylogenies for living taxa, but are generally unattainable for fossils. A distinct advantage of morphology is that some types of morphological data may be collected for extinct and extant taxa. Fossils provide a unique window on evolutionary history and may preserve combinations of primitive and derived characters that are not found in extant taxa. Given their unique character complexes, fossils are critical in documenting sequences of character transformation over geologic time and may elucidate otherwise ambiguous patterns of evolution that are not revealed by molecular data alone. Here, we employ a methodological approach that allows for the integration of molecular and paleontological data in deciphering one of the most innovative features in the evolutionary history of mammals-laryngeal echolocation in bats. Molecular data alone, including an expanded data set that includes new sequences for the A2AB gene, suggest that microbats are paraphyletic but do not resolve whether laryngeal echolocation evolved independently in different microbat lineages or evolved in the common ancestor of bats and was subsequently lost in megabats. When scaffolds from molecular phylogenies are incorporated into parsimony analyses of morphological characters, including morphological characters for the Eocene taxa Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx, the resulting trees suggest that laryngeal echolocation evolved in the common ancestor of fossil and extant bats and was subsequently lost in megabats. Molecular dating suggests that crown-group bats last shared a common ancestor 52 to 54 million years ago.

Animals↗
PubMed1997

The echolocation calls of the spotted bat Euderma maculatum are relatively inaudible to moths

Previous studies of the spotted bat Euderma maculatum have demonstrated that this bat emits echolocation calls that are lower in frequency, shorter in duration and fainter in intensity compared with those of most other insectivorous bats, acoustic characteristics which should render it less conspicuous to eared moths. We tested this prediction by monitoring electrophysiologically the ears of sympatric noctuoid (noctuid, arctiid and notodontid) moths in a site in western Canada. Auditory threshold curves demonstrate that most of the moths tested are less responsive to the calls of Eu. maculatum than to those of another sympatric bat, Eptesicus fuscus. Playbacks to moth ears of pre-recorded search- and approach-phase echolocation calls of Eu. maculatum and Ep. fuscus further demonstrate that the calls of Eu. maculatum are poorly detectable to moths and, in some cases, completely inaudible. We estimate that, in the wild, an average noctuoid moth would detect the calls of Eu. maculatum at distances of less than 1 m as opposed to the calls of Ep. fuscus which should be first heard at distances of 20­25 m. Although most moths are unable to adequately hear Eu. maculatum, the observation that two individuals possessed ears sensitive to this bat's calls suggests the existence of auditory pre-adaptation to this type of echolocation.

Journal Article↗
PubMed1992

Common principle of guidance by echolocation and vision.

1. Using echolocation, bats move as gracefully as birds through the cluttered environment, suggesting common principles of optic and acoustic guidance. We tested the idea by analysing braking control of bats (Macroderma gigas) flying through a narrow aperture with eyes covered and uncovered. 2. Though braking control would seem to require rapid detection of distance and velocity and computation of deceleration, simpler control is possible using the tau function of any sensory variable S that is a power function of distance to aperture. Tau function of S is tau (S) = S/S (the dot means time derivative). Controlled braking is achievable by keeping tau (S) constant. 3. Previous experiments indicated the tau (S) constant procedure is followed by humans and birds in visually controlling braking. Analysis of the bats' flight trajectories indicated they too followed the braking procedure using echolocation. 4. The tau function of echo-delay or of echo-intensity or of angle subtended by directions of echoes from two points on the approach surface could be used to control braking. Aperture size was modulated during flight on some trials in an attempt to test between these possibilities, but the results were inconclusive.

Animals↗
PubMed2003

Object recognition by echolocation: a nectar-feeding bat exploiting the flowers of a rain forest vine.

In the bat-pollinated vine Mucuna holtonii only the first visit to a flower is rewarded with a substantial amount of nectar, which is released when a bat lands on the flower and triggers an explosion mechanism. During later visits the bats receive only small amounts of nectar. Nevertheless, the inflorescences as a whole remain attractive, since further buds successively open during the night. Nectar-feeding bats Glossophaga commissarisi selectively visit unexploded, "virgin" flowers. They can discriminate buds, virgin and exploded flowers using echolocation. In field experiments bats exploited virgin flowers, the vexillum of which had been replaced by a same-sized triple mirror or by an artificial vexillum. Such flowers were frequently inspected, but not as often exploited as natural flowers. In two-alternative-forced-choice experiments the bats learned to discriminate between replicas of the vexillum and triple mirrors. The recognition distance was between 15 and 50 cm. Echoes of the three flowering stages differ in their spectral composition, which changes in dependence of the sound incidence angle in a characteristic way. We conclude that glossophagine bats are able to recognize small motionless structures like flowers and to accurately adjust their landing manoeuvres by using their echolocation system alone.

Animals↗
PubMed2006

The transfer function of a target limits the jitter detection threshold with signals of echolocating FM-bats.

The delay jitter discrimination threshold in bats is a disputed subject. Some investigators have obtained results indicating that bats are able to discriminate alternations in delay down to 10 ns, which appears incredible for purely physical reasons. Using actual bat echolocation sequences recorded during an easy detection task to measure simulated delay jitter, it is shown here that jitter detection thresholds in the order of some tens of nanoseconds are actually physically realizable. However, if the transfer function of the target simulating apparatus is not perfect, the lowest thresholds are in the order of hundreds of nanoseconds and variable between individual bats. This phenomenon is shown to arise as a consequence of the variation in signal parameters from call to call. When the transfer function from a real jitter experiment was artificially applied to the echoes, the jitter detection thresholds again were several hundred nanoseconds. This is the first study to point out a limiting role of the transfer function of a system faced with variations in echolocation signal parameters, something that should be considered in evaluating all sonar systems with variable signal structure.

Acoustic Stimulation↗
PubMed2005

Sensory ecology of predator-prey interactions: responses of the AN2 interneuron in the field cricket, Teleogryllus oceanicus to the echolocation calls of sympatric bats.

We observed the responses of the AN2 interneuron in the Pacific field cricket, Teleogryllus oceanicus, a cell implicated in eliciting avoidance flight away from bats, to acoustic stimuli representing the echolocation calls of bats as well as field recordings of search and gleaning attack calls of six species of insectivorous sympatric bats (West Australia, Australia: Tadarida australis, Chalinolobus goudii, Nyctophilus geoffroyi; Queensland, Australia: Vespadelus pumilus, Myotis adversus; Kaua'i, Hawai'i: Lasiurus cinereus). The broad frequency sensitivity of the AN2 cell indicates that T. oceanicus has evolved to detect a wide range of echolocation call frequencies. The reduced sensitivity of this cell at frequencies higher than 70 kHz suggests that some bats (e.g., the gleaning species, N. geoffroyi) may circumvent this insect's auditory defences by using frequency-mismatched (allotonic) calls. The calls of the freetail bat, T. australis evoked the strongest response in the AN2 cell but, ironically, this may allow this bat to prey upon T. oceanicus as previous studies report that under certain conditions, flying crickets exhibit ambiguous directional responses towards frequencies similar to those emitted by this bat. Short duration calls (1--2 ms) are sufficient to evoke AN2 responses with instantaneous spike periods capable of causing defensive flight behaviours; most bats tested emit calls of durations greater than this. The short calls of N. geoffroyi produced during gleaning attacks may reduce this species' acoustic conspicuousness to this cricket.

Acoustic Stimulation↗
PubMed2001

Frequency discrimination threshold at search call frequencies in the echolocating bat, Eptesicus fuscus.

While searching for prey in open spaces, Epteisicus fuscus emits long-duration, downward frequency-modulated calls which cover a frequency band of about 28-22 kHz. In the ascending auditory pathways of E. fuscus, neurons tuned to these search call frequencies are characterised by a remarkably high frequency selectivity and very sensitive absolute thresholds. We investigated whether this narrow tuning is reflected in an exceptional psychoacoustic frequency discrimination ability. The average frequency difference limen of E. fuscus at search call frequencies determined in a two-alternative, forced-choice experiment amounted to about 420 Hz, corresponding to a Weber ratio of 0.017. This value is similar to those found in non-echolocating mammals, and an order of magnitude larger than the frequency difference limens of bats emitting constant-frequency call components. We discuss these differences in frequency difference limen, and relate them to different echolocation strategies.

Acoustics↗
PubMed1980

Neurons in the cerebellum of echolocating bats respond to acoustic signals.

Single neurons responding to auditory stimuli (40 msec duration, 0.5 msec rise-decay time) could be isolated from rather large areas of the cerebellar vermis and hemispheres of an echolocating bat, Eptesicus fuscus. These neurons had latencies between 4 and 13 msec and best frequencies between 22 and 77 kHz. The Q10-dB values of their tuning curves were between 1.4 and 16.6. When acoustic stimuli were delivered though the earphones, tuning curves measured from each ear alone were nearly identical in shape and best frequency. The minimum thresholds of these neurons were between 12 and 65 dB SPL. Apparently, these are suitable for reception of the bat's echolocating signals.

Acoustic Stimulation↗
PubMed1984

Spatial tuning of auditory neurons in the superior colliculus of the echolocating bat, Myotis lucifugus.

The azimuthal selectivity of auditory neurons was examined in the superior colliculus of the little brown bat, Myotis lucifugus. Frequency-modulated (FM) sounds, synthesized to mimic biosonar signals the echolocating bat naturally hears, were delivered from a loudspeaker moving across the front of the unanesthetized animal. Neurons were classified on the basis of their spatial tuning into two general classes: (i) hemifield units (34%) were broadly tuned to the contralateral side irrespective of sound pressure level; (ii) azimuth-sensitive units (66%) were sharply tuned to different azimuths at sound pressures near their minimum thresholds (MTs). A distinguishing feature of these azimuth-sensitive neurons is that they responded maximally to a sound source located at a preferred azimuth (best azimuth) for levels as high as 30 dB above their MT. Mapping experiments provide evidence of a sequential representation of best azimuth along the rostrocaudal extent of the superior colliculus, with sounds originating from 0-10 degrees ipsilateral coded at the rostral end, and from 30-40 degrees contralateral coded at the caudal end. The highly directional echolocation system of Myotis probably accounts for the limited azimuthal representation of echo-source spanning mainly 40 degrees to either side of its line of flight.

Acoustic Stimulation↗
PubMed1995

Analysis and classification of delay-sensitive cortical neurons based on response to temporal parameters in echolocation signals.

Echolocating bats generate an acoustic image of their target by processing target-reflected echoes of their emitted biosonar pulses. Efforts in building computational models of auditory processing in the bat auditory system, using extensive neurophysiological data from cortical studies are challenged by the intrinsic complexity and the significant variability in neural response to stimuli. In this paper, we use a computerized method for the analysis and classification of delay-sensitive neurons to classify neurons from the auditory cortex of Myotis lucifugus, a species that echolocates with FM signals. The coefficients of the bi-linear fit to the best delay response surfaces (mean R2 = 0.01) were used in classifying the neurons. Six classes were derived that corresponded to the four previously characterized neurophysiologically. The first class corresponded to delay-tuned neurons which exhibited a constant best delay at different pulse repetition rates and pulse durations. Three other classes corresponded to the different subtypes of tracking neurons which changed their best delay to one or both of these stimulus temporal parameters. Two additional classes were differentiated although their best-delay response were similar to either the delay-tuned or the duration and pulse-repetition rate sensitive class. Artificial delay-sensitive neurons built from the parameters of the centroid of each class, will serve a key role in the FM bat auditory system model that we are building.

Acoustic Stimulation↗
PubMed2006

Dissimilarities in the vocal control over communication and echolocation calls in bats.

Bats, like other mammals, use communication calls for social interaction, but rely at the same time on sophisticated echolocation systems for orientation and prey capture. Both call types are of laryngeal origin, but can be distinguished on the basis of their spectral and temporal features and apparently their functional involvement as well. Although they share a common final motor pathway, there is evidence that separate vocally active brainstem areas are involved in the functional control of communication and echolocation calls. This review summarizes findings that support the above assumption, and focus on the functional involvement of the periaqueductal gray, the paralemniscal area, and the nucleus of the brachium of the inferior colliculus, in differentiated vocal control.

Animals↗
PubMedDate not supplied

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.

Animals↗
PubMed1996

Temporal integration in the echolocating bat, Megaderma lyra.

Temporal integration is a crucial feature of auditory temporal processing. We measured the psychophysical temporal integration of acoustic intensity in the echolocating bat Megaderma lyra using a two-alternative forced-choice procedure. A measuring paradigm was chosen in which the absolute threshold for pairs of short tone pips was determined as a function of the temporal separation between the pips. The time constants determined with this paradigm are a crucial characteristic of the sonar system of M. lyra, a species orientating in its environment by very short broadband sonar calls emitted at high rates. Two different carrier frequencies for the tone pips were used to obtain data from the lower and the higher half of the hearing area of M. lyra. Both in the lower and in the higher frequency range, M. lyra showed very short time constants of about 220 microseconds. Our results are comparable to data from the echolocating dolphin, Tursiops truncatus, showing click integration times of about 260 microseconds and to estimates of auditory temporal integration in the context of echo clutter interference in the big brown bat.

Acoustic Stimulation↗